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What does physics study? What branches of physics do you know? What do they study?
Thermodynamics is the branch of physics that studies the relation and conversion of heat and other forms of energy.
Optics is the branch of physics that deals with the phenomenon associated with the spread of electromagnetic waves mainly visible and close to it ranges.
Electrodynamics is the branch of physics that studies the electromagnetic field in the most general case and its interaction with bodies having an electric charge (electromagnetic interaction).
Nuclear physics is the branch of physics that studies the structure and properties of atomic nuclei and their collisions (nuclear reactions).
Atomic physics is the branch of physics that studies the structure and state of the atoms.
What branches of mechanics do you know? What is the object of study of mechanics? What is the kinematics study? What is the mechanical motion?
What methods of describing of position of particle do you know? Describe them. What is reference system? What is reference body? What is the coordinates system?
There are two methods of describing of position of particle in the space:
1)through coordinates (Cartesian coordinates system)
2)with help of radius vector.
Reference system in plane a system that uses coordinates to establish position. It has origin – reference body with coordinates (0;0), and two lines – coordinate axis of the system divided into equal fixed segments.
Any point in coordinates method can be described by pair of numerical coordinates. In the second method any point can be described by vector, tail of which in the origin and head in point where particle is situated.
What is the material point? What is the radius vector? What is the rigid body?
Material point is the body size and shape of which can be neglected in given problem.
Radius vector is a vector defining the position of a point in space with respect to a pre-fixed point called the origin.
Rigid body is an idealized model, set of points, the distance between the current positions do not change, no matter what influences the body in motion is subjected to.
What is the motion equation? What is the trajectory equation?
Motion equation is an equation or system of equations defining the law of change the position of the mechanical dynamic system in time and space.
The trajectory of a material point - line in space, which is a set of points, which was, is or will be a material point in its movement in space with respect to the chosen reference system. Equation of trajectory describes position of particle in the space at any time.
What is straight lined motion? What is curvilinear motion? What is translational motion? What is rotational motion?
Straight lined motion is the mechanical motion in which the displacement vector Δr does not change direction; its magnitude is the length of the path traveled by the body.
Curvilinear motion is a movement which trajectory is a curved line (for example, circle, ellipse, hyperbola and parabola).
Translational motion is the mechanical motion system of points (of a rigid body), in which every line segment associated with the moving body remains parallel to its position at any previous time.
Rotational motion rigid body is the mechanical motion when all its points describe circles, arranged in parallel planes. The centers of all circles lie on a line perpendicular to the plane of the circle and called the axis of rotation.
What is the displacement vector of a particle? What kind of value is the velocity? What is the average velocity? What is the instantaneous velocity?
Displacement vector is the vector which connects initial and final positions of the particle.
Velocity is the vector value, which is characterized with magnitude and direction. It is a change of displacement vector over time when that change occurred.
Average velocity is atotaldistance of a particle over total time, when particle moved through that distance.
Instantaneous velocity is the time derivative of displacement vector.
What kind of value is the acceleration? What is the average acceleration? What is the instantaneous acceleration? What components of acceleration do you know? Give them definitions.
Acceleration is a vector value, which characterize change of velocity over time, when that change occurred.
Average acceleration is a difference of initial and final velocity of a particle over time whole, when that change occurred.
Instantaneous acceleration is the time derivative of velocity.
Tangential acceleration is a component of total acceleration in curvilinear motion, which characterize changing of magnitude of velocity and directed as same as velocity vector.
Normal acceleration is the component of total acceleration in curvilinear motion, which characterize changing of direction of velocity vector, and directed perpendicular to the tangential acceleration, to the center of circle.
Which motion is called uniform motion? Which motion is called uniformly accelerated motion? Which motion is called uniformly decelerated motion?
Uniform motion is the mechanical motion in which the body for any equal intervals of time passes the same distance, so velocity of this body is constant.
Uniformly accelerated motion is a motion when vector of acceleration, which is not equal zero, does not change during time interval and directed the same as velocity vector.
Uniformly decelerated motion is a motion when vector of acceleration, which is not equal zero, does not change during time interval and directed the oppositely to the velocity vector.
For example: motion of the body, which was thrown at an angle from the horizon. Vector of acceleration (free falling acceleration) is constant value and directed perpendicular to the surface of the Earth.
What is the polar coordinate system? What is the angle of rotation? What is the angular velocity? What is the angular acceleration? What is called period and frequency?
Polar coordinate system is the two-dimensional coordinate system in which each point on the plane is defined by two numbers - the polar angle and polar radius.
Angular velocity characterizes the rate of rotation around the center of mass point of rotation. The angular velocity for the magnitude equal to the angle of rotation around the center point of rotation per unit time:
Angular accelerationcharacterizes the rate of change of the angular velocity of the material point. For magnitude it equals time derivative of angular velocity.
Angle of rotation characterizes the rotation of the body, or rotating beam emitted from the center of rotation of the body, relatively to the other beam which is considered fixed.
Periodis the time of one total rotation of body around rotation axis.
Frequency is the amount rotations over per unit time.
How do you understand the concept of relativity? What is the object of studying of dynamics?
The theory of relativity, or simply relativity in physics, usually encompasses two theories by Albert Einstein: special relativity and general relativity. Albert Einstein, in his theory of special relativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.
The object of study of dynamics is the reason of motion, forces.
What kinds of interactionsexist in nature? Describe their nature. Define their radius of action.
There are four types of interaction:
1) gravitational
2) electromagnetic
3) strong
4) weak.
Gravitational interaction exists between objects with mass, electromagnetic interaction occurs when bodies are charged. These two interactions have very wide radius of action. Strong interaction occurs into the atom, weak – in the molecule.
Which body is called free? What is the field in physics? What is the force? Where lays the point of acting of gravity forces and where it is directed?
Body can be called free if there are no any forces which are acting on it.
Field is the special form of matter via which bodies interact with each other (gravitational field, electromagnetic field).
The force is any influence that causes an object to undergo a certain change, either concerning its movement, direction, or geometrical construction.
Point of acting of gravity force is called center of mass of that body. The force is directed to the center of Earth.
What forces in mechanics do you know? Formulate the laws of Newton. What is inertial reference system?
The force of gravity exerted on an object is equal to the product of its mass (a scalar quantity) and the free-fall acceleration: F=mg
Elastic force, it’s a force arising from the deformation of a solid body which depends only on the body's instantaneous deformation and not on its previous history, and which is conservative.
The friction force is a force that is created whenever two surfaces move or try to move across each other.
F=µN; N=mg
Newton’s second law of motion – the acceleration of an object is directly proportional to the resultant force acting on it; The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
Newton’s third law; third law of motion; third principle of dynamics – if two objects interact, the force exerted by object 1 on object 2 is equal in magnitude to and opposite in direction to the force exerted by object 2 on object 1.
What is the gravitational force? Formulate the law of universal gravitation. What is the inertial and gravitational mass?
Newton’s law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
where F – is the force between the masses, G – is the gravitational constant, m1 – is the first mass, m2 – is the second mass, r – isthe distance between the centres of the masses.
Inertial mass is a measure of an object’s resistance to changing its state of motion when a force is applied. An object with small inertial mass will accelerate more than an object with large inertial mass when acted upon by the same force.
Gravitational mass is the physical property of an object that causes it to interact with other objects through the gravitational force. According to the equivalence principle, gravitational mass is equivalent to inertial mass.
What is the momentum of a particle? Formulate the laws of conservation of energy and momentum for a system of particles.
Momentum of a particle is the product of the mass and velocity of a particle.
Where m – mass, v – velocity.
Law of conservation of energy for a system of particles: the total energy of the system of particles is costant? When this system is isolated (no external forces act on the system).
- mechanical case, T – kinetic, V – potential energy.
Law of conservation of momentum for a system of particles: in an isolated system of particles the total momentum is constant.
For example, two particles interact. Because of Newton’s third law, the forces between them are equal and opposite.
; . Therefore: or
- case of two particles.
- law of conservation of momentum.
Formulate the universal law of conservation of energy. Derive theoretically the momentum conservation law.
Energy can neither be created (produced) nor destroyed by itself. It can be only transformed from one form to another, but the total energy of an isolated system is always constant.
According to the second Newton’s law for the system of N particles:
where momentum of the system
and — the resultant of all the forces acting on particles of the system
Here — the resultant of the forces, acting on the n-th particlefrom side of m-th, and — the resultant of all external forces acting on k-th particle.According to the third Newton's law, power type and will be equal to the absolute value and opposite in direction, i.e. . Therefore, the second sum in the right-hand part of the expression (1) is equal to zero, we obtain that the derivative of momentum in the system over time is equal to the vector sum of all external forces acting on the system:
Internal forces are excluded by Newton's third law.
For systems of N particles in which the sum of all external forces is equal to zero
or for systems, on the particles of which, no external forces act (for all k from 1 to n), we have
As you know, if derivative from an expression is zero, the expression has a constant value with respect to the variable differentiation, so:
(constant vector).
That is, the total momentum of the system of N particles, where N any integer, is a constant value.
What is called the gravitational potential energy?
Gravitational potential energy is energy an object possesses because of its position in a gravitational field.
For objects near the Earth the acceleration of gravity g can be considered to be approximately constant and the expression for potential energy relative to the Earth's surface becomes
whereh is the height above the surface and g is the surface value of the acceleration of gravity.
What is called the kinetic energy?
In physics, the kinetic energy of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body in decelerating from its current speed to a state of rest.
What is a body weight?
The term body weight is used colloquially and in the biological and medical sciences to refer to a person's mass or weight.
What is called scalar product of vectors?
An angle α between non-zero vectors AB and CD is an angle, formed at a parallel transfer one of the vectors till coinciding the points A and C. A scalar product of vectors a and b is called a number, equal to a product of lengths ( modules )of these vectors by cosine of angle between them:
Примечание: стоит нарисовать векторную диаграмму, обозначив все вектора и угол.
What force is called conservative?
A conservative force is a force with the property that the work done in moving a particle between two points is independent of the taken path. Examples: gravitational force, Coulombs force, elastic force.
What force is called nonconservative?
Nonconservative forces are forces, which depend on the way of transition of a body or system from the initial position to the end position. The work of these forces on the closed trajectory is different from zero. Example: friction force, traction force (сила тяги).
Which values are called scalar values?
Scalar values are characterized only by magnitude. Example: time, temperature.
Which values are called vector values?
Vector values are characterized by magnitude and direction. Example: velocity, force,est.
What rules of vector addition do you know? Describe and draw.
The parallelogram law
The triangle law
What is the working of force on the movement of particle?
Work is the scalar product of the force vector and the practice displacement vector. Mesured in joules.
What is the power of force?
Power is the amount of energy (done work of force) consumed per unit time. Measured in watts.
Describe the rules of vector addition. Draw.
The parallelogram law
The triangle law
Which fundamental values are constant in physics?
In physics, there are a number of constants, which, according to recent data, have the same value at any point in the observable universe, so they are called fundamental, or the worldconstants. These are constant: the constant of gravity, the Planck constant, the speed of light, the mass of the proton, the electron mass, the Hubble constant (for our age) and several other.
What limits are applied to conservation laws?
In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves.A partial listing of conservation laws that are said to be exact laws, or more precisely have never been [proven] to be violated:Conservation of mass-energy, Conservation of linear momentum, Conservation of angular momentum, Conservation of electric charge.
There are also approximate conservation laws. These are approximately true in particular situations, such as low speeds, short time scales, or certain interactions. Approximate conservation law: Conservation of mass (applies for non-relativistic speeds and when there are no nuclear reactions), Conservation of baryon number (See chiral anomaly), Conservation of lepton number (In the Standard Model), Conservation of flavor (violated by the weak interaction).
In physics, the law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time.
In real processes, where a frictional force, there is a deviation from the law of conservation of mechanical energy. For example, when the body falls to Earth first kinetic energy of the body increases as speed increases. The sum of kinetic and potential energy of all the bodies of the system remains constant.
The law of conservation of mass, or principle of mass conservation, states that for any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed.
This law applies only for non-relativistic speeds and when there are no nuclear reactions.
What is the natural satellite of the Earth?
The natural satellite of the Earth is the Moon.
What is nature of gravitational forces?
Any object (particle) with mass has a gravitational field around it.
What is the nature of electromagnetic forces?
Any charged object (particle) has an electromagnetic field around it.
How can we calculate a density of the body, if we know mass and volume of that body?
To calculate a density of given body we need to divide mass by volume.
What is the reason of motion?
Motion is the result of an unbalanced force. Body motion can only occur in relation to other bodies and related spaces.
Which interaction is responsible for the transformation of particles? Weak interaction is responsible foe the transformation of particles. Which geometrical shapes do you know?
Polygon – a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed chain or circuit. These segments are called its edges or sides, and the points where two edges meet are the polygon's vertices (singular: vertex) or corners.
Triangle a polygon with three corners or vertices and three sides or edges which are line segments.
Parallelogram is a simple quadrilateral (четырёхугольник) with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure.
Circle is the set of all points in a plane that are at a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius.
1.How can we measure the rotation angle of particle in uniform circular motion? Can we compare values of different dimensions? Give an example.
Let a material point moves in a circle of radius R. We introduce a Cartesian coordinate system whose origin is compatible with the center of the circle (Fig. 74). Position of a point on the circle is uniquely determined by the angle φ between the X axis and the radius vector of the point.
рис. 74
Cartesian coordinates of the point can be uniquely expressed through the angle formulas:
When the coordinate points of its movement, i.e. the rotation angle is changed, becomes a function of time. Therefore, the law of motion in this case represented by the function φ (t), that is, depending on the angle of rotation from time to time.
By analogy, we introduce the concept of a one-dimensional movement of the angular velocity.
Angular velocity ω is the ratio of the rotation angle to the length of time during which this change occurs, during the time interval tends to zero:
The unit of the angular velocity is rad / s - radians per second, but since radians is dimensionless, the dimension of the angular velocity can be simply 1 / c = 1 - a second power minus one.
2. We can’t compare values of different dimensions, for example 1 meter and 1 foot, or 1 degree and 1 radian. We need to convert feet to meter and find out that 1 foot =0.3048 m, and 1 radian≈57.324 degrees.
What conditions are imposed on conservation laws in physics?
In physics, the law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time. Energy can be neither created nor destroyed, but can change form, for instance chemical energy can be converted to kinetic energy in the explosion of a stick of dynamite.
A consequence of the law of conservation of energy is that a perpetual motion machine of the first kind cannot exist. That is to say, no system without an external energy supply can deliver an unlimited amount of energy to its surroundings.
What data can be taken from experiments in mechanics?
‘In the matter of physics, the first lessons should contain nothing but what is experimental and interesting to see. A pretty experiment is in itself often more valuable than twenty formulae extracted from our minds.’ - Albert Einstein
‘Experimental mechanics’ can be defined as the investigation by experimental means of the mechanical behaviour of engineering systems subjected to load. Experimental mechanics approaches that provide a measure related to the strain are therefore very important design tools. Many of these techniques have been available for decades but recently have been gaining popularity because of the advances in computing power and decreasing hardware costs. More importantly from the design perspective, the necessity for experimental data to validate numerical models of systems manufactured from complex nonlinear inhomogeneous materials, such as fibre reinforced polymer composites, is ever increasing. Experimental mechanics approaches have much to offer and it is the purpose of this module to provide an overview of the range of application and operation of the techniques.
What cause the decrease or increase in value if it is directly (inversely) proportional to a known value? What determines the first derivative of the function of one variable?
Increase or decrease in value cased by proportionality to known value. For example, let’s take Newton’s second law. Acceleration is directly proportional to force and inversely proportional to the mass of body. It means that if mass is constant and force is increasing, we will take increasing value of acceleration because 10,100,1000 N over 10 kg in first situation equal 1, in second 10 and 100 m/s2 in third, and vice versa if acting force is constant and mass is growing, we will take decreasing value of acceleration.
First derivative of the function of one variable determines rate of changing of the function.
What movement called limited and unlimited? What determines the work of moving particle in the field of conservative forces?
A conservative forceis a force with the property that the workdone in moving a particle between two points is independent of the path taken. Equivalently, if a particle travels in a closed loop, the net work done (the sum of the force acting along the path multiplied by the distance travelled) by a conservative force is zero.[2] A direct consequence of the closed path test is that the work done by a conservative force on a particle moving between any two points does not depend on the path taken by the particle. Also the work done by a conservative force is equal to the negative of change in potential energy during that process. There is zero net work (W) done by the force when moving a particle through a trajectory that starts and ends in the same place:
What is the duration of one complete revolution of the Earth around the Sun? How to get the equation of the trajectory from the equations of motion?
The earth's revolution around the earth is also called an orbit. The earth which is about one hundred fifty kilometers away from the sun rotates around it. It takes the earth about 365.25 days to make a whole revolution around the sun. More accurately, this translates into 365 days 5 hours 59 minutes 16 seconds
For each meaning of time t in equation of motion we can determine the coordinates of the point (moving body) at this point and specify its position in space. Giving all possible values of t, we obtain a variety of positions of the moving point in space - its trajectory.
What is the magnitude of the increment?
The definition for magnitude as it applies to Physics is simple. Magnitude is the value of an object, such as the magnitude of velocity would be speed.
What is an infinitesimal increment function?
The change in velocity is related to the same infinitesimal increment of time dt, but to different powers of forces,i.e. dc=pdt dc=dt and dc=.The mathematical relation between the infinitesimal increment of velocity dc and the infinitesimal increment of the time variable Δt.
What is the center of mass of the system of the particles? What values are inversely proportional? Directly proportional?
In physics, the center of mass of a distribution of mass in space is the unique point where the weighted relative position of the distributed mass sums to zero. The distribution of mass is balanced around the center of mass and the average of the weighted position coordinates of the distributed mass defines its coordinates. Calculations in mechanics are often simplified when formulated with respect to the center of mass.
A system of particles
In the case of a system of particles Pi, i = 1,2…,n, each with mass mi that are located in space with coordinates ri, i = 1,2…,n, the coordinates R of the center of mass satisfy the condition
Solve this equation for R to obtain the formula
where M is the sum of the masses of all of the particles.
In mathematics, two variables are proportional if a change in one is always accompanied by a change in the other, and if the changes are always related by use of a constant. The constant is called the coefficient of proportionality or proportionality constant.
What is matter? What mechanical phenomena can be observed in nature? Objects that take up space and have mass are called matter. Everything around you is made up of matter.
Matter commonly exists in four states (or phases): solid, liquid and gas, and plasma. However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also leads to new phases of matter, such as the quark–gluon plasma.[5] For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).
Mechanical phenomena in nature.
Mechanical: moving of animals, flying of the birds, ect.
Thermal: conversion of water to ice, conversion of water to vapour…
Electric: lightning
Sound: thunder, rustle of leaves
Light: sunshine, shining of the stars, ect.
What kind of relationship variables in mechanics do you know? Describe their physical meaning. What is the abscissa, ordinate, applicate?
In mathematics, abscissa (plural abscissae or abscissæ or abscissas) most often refers to the horizontal coordinate of a point in a two-dimensional rectangular Cartesian coordinate system. The term can also refer to the horizontal axis (typically x-axis) of a two-dimensional graph (because that axis is used to define and measure the horizontal coordinates of points in the space). An ordered pair consists of two terms—the abscissa (horizontal, usually x) and the ordinate (vertical, usually y)—which define the location of a point in two-dimensional rectangular space.
In mathematics, ordinate most often refers to that element of an ordered pair which is plotted on the vertical axis of a two-dimensional Cartesian coordinate system, as opposed to the abscissa. The term can also refer to the vertical axis (typically y-axis) of a two-dimensional graph (because that axis is used to define and measure the vertical coordinates of points in the space). An ordered pair consists of two terms—the abscissa (horizontal, usually x) and the ordinate (vertical, usually y)—which define the location of a point in two-dimensional rectangular space.
Velocity V
m s−1
Acceleration a m s−2
Angularvelocity ω rad s−1
What is an ideal gas? What bodies are in thermal equilibrium?
Ideal gas – is a model in which the molecules do not interact with each other.
The average separation between molecules is great compared with their dimensions.
Two bodies are in thermal equilibrium with each other if they have the sametemperature.
Thermal equilibrium of an isolated body
Thermal equilibrium of a body in itself refers to the body when it is isolated. The background is that no heat enters or leaves it, and that it is allowed unlimited time to settle under its own intrinsic characteristics. When it is completely settled, so that its temperature is spatially and temporally uniform, it is in its own thermal equilibrium. It is not implied that it is necessarily in other kinds of internal equilibrium. For example, it is possible that a body might reach internal thermal equilibrium but not be in internal chemical equilibrium; glass is an example.
The relation of thermal equilibrium between two thermally connected bodies
The relation of thermal equilibrium is an instance of a contact equilibrium between two bodies. This means that it refers to transfer through a selectively permeable partition, the contact path.[1] For the relation of thermal equilibrium, the contact path is permeable only to heat; it does not permit the passage of matter or work. According to Lieb and Yngvason, the essential meaning of the relation of thermal equilibrium includes that it is reflexive and symmetric. It is not included in the essential meaning whether it is or is not transitive. After discussing the semantics of the definition, they postulate a substantial physical axiom, that they call the "zeroth law of thermodynamics", that thermal equilibrium is a transitive relation. They comment that the equivalence classes of systems so established are called isotherms
Describe the Zeroth Law of Thermodynamics
The "zeroth law" states that if two systems are at the same time in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
If A and C are in thermal equilibrium with B, then A is in thermal equilibrium with C. Practically this means that all three are at the same temperature, and it forms the basis for comparison of temperatures. It is so named because it logically precedes the First and Second Laws of Thermodynamics.
There are underlying ideas about heat associated with the zeroth law of thermodynamics, and one of those ideas was expressed by Maxwell as "All heat is of the same kind." If A is in thermal equilibrium with B, then every unit of internal energy that passes from A to B is balanced by the same amount of energy passing from B to A. This is true even if the atomic masses in A are different from those in B, and even if the amount of energy per unit mass in A is different because the material has a different specific heat. This implies that there is a measurable property that can be considered to be the same for A and B, a property upon which heat transfer depends. That property is called temperature.
What is the Internal Energy?
The internal energy of a system is identified with the random, disordered motion of molecules; the internal energy in a system includes potential and kinetic energy. This is contrast to external energy which is a function of the sample with respect to the outside environment (e.g. kinetic energy if the sample is moving or potential energy if the sample is at a height from the ground). The symbol for Internal Energy Change is ΔU.
Energy on a smaller scale:
Internal Energy Change Equations ΔU = Q+W, where Q is heat and W is work.
What is Heat?
The quantity of energy transferred as heat is a scalar expressed in an energy unit such as the joule (J), with a sign that is customarily positive when a transfer adds to the energy of a system. It can be measured by calorimetry.
What is the heat capacity?
The heat capacity of a defined system is the amount of heat needed to raise the system's temperature by one degree. It is expressed in units of thermal energy per degree temperature. To aid in the analysis of systems having certain specific dimensions, molar heat capacity and specific heat capacity can be used.
Molar Heat Capacity
The amount of heat needed to increase the temperature of one mole of a substance by one degree is the molar heat capacity. It is expressed in joules per moles per degrees Celsius (or Kelvin), Joules/Moles∘C (K).
Specific Heat Capacity
The amount of heat needed to increase the temperature of one gram of a substance by one degree is the specific heat capacity. It is expressed in joules per gram per degree Celsius, Joules/Grams∘C.
Describe the First Law of Thermodynamics
The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes:
The first law makes use of the key concepts of internal energy, heat, and system work. The standard unit for all these quantities would be the joule, although they are sometimes expressed in calories.
It is typical for chemistry texts to write the first law as ΔU=Q+W. It is the same law, of course - the thermodynamic expression of the conservation of energy principle. It is just that W is defined as the work done on the system instead of work done by the system.
What is the adiabatic process? Isobaric, Isochoric, Isothermal
An adiabatic process is one in which no heat is gained or lost by the system. The first law of thermodynamics with Q=0 shows that all the change in internal energy is in the form of work done: ΔU= - W. ΔW equals the change in a physical property of the system. A physical property of the system depends only on the state of the system (P, V, T), not on the way the system was put into this state.
An isobaric process is a process that occurs at constant pressure. We then have W = P(V2 - V1). If the pressure of an ideal gas is kept constant, then the temperature must increase as the gas expands. (PV/T = constant). For an isobaric process we write ΔU = ΔQ - ΔW = ΔQ – P (V2 - V1).
An isochoric process takes place at constant volume. Then W = 0 and ΔU = ΔQ. All the heat added to the system goes into increasing its internal energy.
An isothermal process occurs at constant temperature. Since the internal energy of a gas is only a function of its temperature, ΔU = 0 for an isothermal process. Since ΔU = 0, the heat transferred to the gas is ΔQ = W.
Describe the molecular model for an ideal gas
Ideal gas: A theoretical gas composed of randomly moving non-interacting particles. At normal conditions such as standard temperature and pressure, most real gases behave qualitatively like an ideal gas.
Kinetic model of an ideal gas: A model which treats a gas as many molecules subject to the following assumptions:
· The molecules obey Newton’s laws
· The intermolecular forces are negligible
· The molecules are spherical with negligible volume
· The motion of the molecules is random
· The collisions are perfectly elastic
· The time taken for a collision is negligible.
The ideal gas equation is: or
Universal Gas Constant:
Describe relationship between pressure and molecular kinetic energy.
What is the degree of freedom? Specify the energy equipartition theorem.
In many scientific fields, the degrees of freedom of a system is the number of parameters of the system that may vary independently. For example, the position of a figure in the plane has three degrees of freedom: its orientation and the two coordinates of any fixed point of the figure.
In mathematics, this notion is formalized as the dimension of a manifold or an algebraic variety. When degrees of freedom is used instead of dimension, this usually means that the manifold or variety that models the system is only implicitly defined.
The theorem of equipartition of energy states that molecules in thermal equilibrium have the same average energy associated with each independent degree of freedom of their motion and that the energy is the equipartition result
Specify The Boltzmann distribution law.
The Boltzmann distribution law says that if the energy associated with some state or condition of a system is ε then the frequency with which that state or condition occurs, or the probability of its occurrence, is proportional to
(1.1)
where T is the system’s absolute temperature and where k is the Boltzmann constant, which the reader will already have encountered in the kinetic theory of gases:
k = 1.38×10−23 J/K = 1.38×10−16 erg/K.
What is The Maxwell–Boltzmann distribution functions?
Maxwell's law gives the distribution of the particle kinetic energy , and Boltzmann's law - the distribution of particles on the values of the potential energy . Both distributions can be combined into a single law Maxwell – Boltzmann
Here n0 - number of molecules per unit volume at the point where U = 0 , E = U + K - total energy .
In the last expression , the potential and kinetic energy , and hence the total energy E , can take a continuous range of values. If the energy of the particle can take only a discrete set of values E1, E2, ..., ( as is the case , for example, the internal energy of the atom) , then the Boltzmann distribution has the form :
where Ni - the number of particles in a state with energy Ei, and A> - coefficient of proportionality , which must satisfy the condition
where N - total number of particles in the system.
Then the final expression of the Maxwell distribution - Boltzmann case of discrete energy values will be:
What is the mean free path? What is a heat engine?
In physics, the mean free path is the average distance travelled by a moving particle (such as an atom, a molecule, a photon) between successive impacts (collisions),which modify its direction or energy or other particle properties.
The mean free path or average distance between collisions for a gas molecule may be estimated from kinetic theory. Serway's approach is a good visualization - if the molecules have diameter d, then the effective cross-section for collision can be modeled by
using a circle of diameter 2d to represent a molecule's effective collision area while treating the "target" molecules as point masses. In time t, the circle would sweep out the volume shown and the number of collisions can be estimated from the number of gas molecules that were in that volume.
A heat engine typically uses energy provided in the form of heat to do work and then exhausts the heat which cannot be used to do work. Thermodynamics is the study of the relationships between heat and work. The first law and second law of thermodynamics constrain the operation of a heat engine. The first law is the application of conservation of energy to the system, and the second sets limits on the possible efficiency of the machine and determines the direction of energy flow
Heat engines are typically illustrated on a PV diagram
How do like and unlike charges behave? Specify the properties of the charge.
Like charges repel, unlike charges attract each other.
Properties of electric charge:
1.Two kinds of charges occur in nature, with the property that unlike charges
attract one another and like charges repel one another.
2. Charge is conserved.
3. Charge is quantized.
What is the conductors and semiconductors?
It is convenient to classify substances in terms of their ability to conduct electric charge:
Electrical conductors are materials in which electric charges move freely, whereas electrical insulators are materials in which electric charges cannot move freely. Metals are good conductors.
Semiconductors are a third class of materials, and their electrical properties are somewhere between those of insulators and those of conductors. grounded. induction.
Different Types of Conductors
a) Metals are traditional conducting materials. You see them around the house all of the time. It's a metal wire or one of the metal prongs in an electric plug. There are a lot of free electrons in metallic conductors. Free electrons are electrons that are not being held in atoms, and so, can move easily. Some of the best metallic conductors are copper (Cu), silver (Ag), and gold (Au).
b) A semiconductor is a material which has electrical conductivity to a degree between that of a metal (such as copper) and that of an insulator (such as glass). Semiconductors are the foundation of modern electronics, including transistors, solar cells, light-emitting diodes (LEDs), quantum dots and digital and analog integrated circuits.
Give a definition of Coulomb’s law.
Coulomb’s experiments showed that the electric force between two stationary charged particles:
1. is inversely proportional to the square of the separation r between the particles and directed along the line joining them;
2. is proportional to the product of the charges q1 and q2 on the two particles;
3. is attractive if the charges are of opposite sign and repulsive if the charges have the same sign.
Force acting between two charged particles is directly proportional to product of charges of these particles and inversely proportional to squared distance between these particles.
Where k-coefficient of proportionality, which is equal k=9*109 (N*m2)/K2.
What is the electric field strength?
Electric field is said to exist in the region of space around a charged object. the electric field E at a point in space is defined as the electric force Fe acting on a positive test charge q0 placed at that point divided by the magnitude of the test charge:
Formulate rules for the geometric description of the electric field lines.
Rules for drawing electric field lines
• The lines must begin on a positive charge and terminate on a negative charge.
• The number of lines drawn leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge.
• No two field lines can cross. When a particle of charge q and mass m is placed in an electric field E, the electric force exerted on the charge is qE. If this is the only force exerted on the particle,
it must be the net force and so must cause the particle to accelerate. In this case, Newton’s second law applied to the particle gives
The acceleration of the particle is therefore
If E is uniform (that is, constant in magnitude and direction), then the acceleration is constant. If the particle has a positive charge, then its acceleration is in the direction of the electric field. If the particle has a negative charge, then its acceleration is in the direction opposite the electric field.
What distribution of charge on volume, to the surface and length?
If the charged body is so great, that he can not be examined as a point charge, then in this case it is necessary to know distribution of charges into a body, the spatial location of charges it is accepted to describe with a help: to the b.d. of charge(r), superficial closeness of charge(s) and linear closeness of charge(l). These sizes are determined by formulas:
b.d. of charge of r
superficial closeness of charge of s
What is the acceleration of particle equal to charge of q and the masses of m in the electric field of Е?
In accordance with the law of Coulomb electrostatic field created by a point charge Q at a distance r from it, is equal in absolute value:
This field is called Coulomb. In the Coulomb field vector direction depends on the sign of the charge Q: if Q> 0, then the vector is directed along the radius of the charge, if Q <0, the vector is directed to the charge.
In the present problem for the calculation of the formula can be applied field strength in the capacitors:
Here U - voltage between the capacitor plates, d - the distance between the plates.
The force with which the field acts on the charge calculated by the formula F = Eq. However, according to Newton's second law, we obtain an expression for the field with known charge, mass and acceleration: E = ma / q.
What is the electrical equilibrium? Specify properties of conductors in equilibrium.
When there is no net motion of charge within a conductor, the conductor is in electrostatic equilibrium
A conductor in electrostatic equilibrium has the following properties:
1. The electric field is zero everywhere inside the conductor; no electric field can exist inside a conductor. However, this statement is true only if the conductor is in static equilibrium.
2. Any net charge on the conductor resides entirely on its surface.
3. The electric field just outside the conductor is perpendicular to its surface and has a magnitude where _ is the surface charge density at that point.
4. On an irregularly shaped conductor, the surface charge density is greatest where the radius of curvature of the surface is the smallest.
What is electric current? Give definition to average electric current and moment meaning of the electric current.
Now consider a system of electric charges in motion.
Suppose that the charges are moving perpendicular to a surface of area A, as shown in Figure
(This area could be the cross-sectional area of a wire, for example)
The current is the rate at which charge flows through this surface.
If ΔQ is the amount of charge that passes through this area in a time interval Δt, the average current Iav is equal to the charge that passes through A per unit time:
We define the instantaneous current I as the differential limit of average current:
What is the current density in the conductor? Specify Ohm's law.
The current density J in the conductor is defined as the current per unit area.
for many materials (including most metals), the ratio of the current density to the electric field is a constant σ that is independent of the electric field producing the current.
Ohm's Law deals with the relationship between voltage and current in an ideal conductor. This relationship states that:
The potential difference (voltage) across an ideal conductor is proportional to the current through it.
The constant of proportionality is called the "resistance", R.
Ohm's Law is given by:
U = I R
What is the resistance of a conductor? What is a superconductor?
Electric resistance is a physical size, characterizing properties of explorer to prevent to passing of electric current and equal to the relation of tension on the ends of explorer to strength of current aleak on him. Resistance for the chains of alternating current and for the variables of the electromagnetic fields is described by the concepts of impedance and impendance. By resistance(by a resistor) of предназначан for introduction to the electric chains of pure resistance.
Superconductivity is property of some materials to possess strictly a zero electric resistance at an achievement by them temperatures of the below defined value(critical temperature). Several hundred and керамик, passing to the state, connections, clean elements, alloys, are known. Superconductivity is the quantum phenomenon. It is characterized also the effect of Мейснера consisting in the complete forcing of magnetic-field out of volume of superconductor. Existence of this effect shows that superconductivity