chapter 22 capacitance; dielectrics; electric energy storage (2)
chapter 19~22 test
1、what happens when a charged insulator is placed near an uncharged metallic object? a、they attract each other. b、they repel each other. c、they may attract or repel each other, depending on whether the charge on the insulator is positive or negative. d、they exert no electrostatic force on each other.
2、about gauss's law, which of the following statements is true? a、if the electric flux through a closed surface is zero, there must be no charge inside the closed surface. b、if there is no charge inside the surface, the electric field inside the surface is zero. c、if the electric field inside the closed surface is uniform, there is no charge inside the closed surface. d、if there is no net charge inside the surface, the electric field over the enclosed surface must be zero.
3、about the electric fluxes φe through each gaussian surface shown in the figure, which of the rankings is correct? a、 b、 c、 d、
4、which of the following figures about field line can represent an electrostatic field in real world? a、figure a b、figure b c、figure c d、figure d
5、if three unequal capacitors, initially uncharged, are connected in series across a battery, which of the following statements is true? a、the largest voltage appears across the smallest capacitance. b、the capacitor with the largest capacitance has the greatest charge. c、the equivalent capacitance is greater than any of the individual capacitances. d、none of the others is true.
6、in the figure, charges are placed on the piece of conductor. how is the charges distributed on the object? a、uniformly over the surface. b、with greatest density near point e on the flat surface. c、with greatest density near point d in the interior. d、with greatest density near point c on the surface.
7、if the following devices are all uniformly charged, which of them can produce a uniform electric field? a、infinitely long straight line b、circular ring c、solid sphere d、solid sphere with a spherical hole inside it
8、if several charges are present, the net force on any one of them will be the algebraic sum of forces due to each of the others.
9、for electrostatic field, there are no closed field lines.
10、if the electric flux through a closed surface is 0, then there is no net charge inside the surface.
11、gauss's law is valid only when the charge distribution is highly symmetric.
12、if a conductor is in an electrostatic equilibrium, then the electric field inside it at any position is 0.
13、the linear integral of electrostatic field along a closed path is determined by the net charge inside.
14、a conductor in electrostatic field is an equipotential body, any two points on the conductor have the same electric potential.
15、the capacitance of a capacitor usually depends on its size, shape, relative position of two conductors, and voltage between two conductors.
16、a conductor spherical shell carries charge q=3c, another point charge q=2c is located inside the shell. how much is the electric charge distributed on the outer surface of the conductor shell? q'=______________c
17、a thin rod is uniformly charged (q, l). how much is the electric potential for point p in the figure? (3 significant numbers)
18、consider a uniformly charged semi-circle with charge q and radius r, what is the electric field at the center point? (3 significant numbers)
19、a point charge q is placed at the center of a cube as shown in figure, the electric flux through each face of the cube is: (3 significant numbers)
20、how does the capacitance change if a capacitor c is half filled with dielectric (k=2) as shown in figure? c'=_________c
chapter 26 sources of magnetic field (2)
chapter 25~26 test
1、which of the following devices can produce a uniform magnetic field? a、infinitely long straight current b、circular current c、infinitely long solenoid d、ring shape toroid
2、if a small circular current is placed in a uniform magnetic field, at which angle θ there will be maximum torque acting on the circular current? a、0 b、π/4 c、π/2 d、π
3、there are some statements about hall effect. which of them is not correct? a、there will be a voltage across a current-carrying conductor if it is placed in a magnetic field. b、the charges can escape from the metal surface when they absorb enough energy. c、there are more than one force acting on the moving charges. d、hall effect can be used to distinguish p-type and n-type semiconductors.
4、infinitely long current i1 and circular current i2 are insulated, and they lie on the same plane. what is the direction of magnetic force acting on current i2? a、 x direction b、- x direction c、 y direction d、- y direction
5、magnetic field lines are closed field lines without beginning or end.
6、the total magnetic flux through a closed surface is determined by the current inside.
7、magnetic field is a conservative field.
8、if there is only magnetic force acting on an object, its kinetic energy will not change.
9、consider an equilateral triangle wire (length l=0.1m for each side) with current i=2a, how much is the magnetic field produced at its center o?
10、when using ampere’s law, we have to know how much the current passing through the area enclosed by the chosen path is. in the following figure,
chapter 29 maxwell’s equations and em waves (2)
chapter 27~29 test
1、there are some equations and statements about the electrostatic field e0 and induced electric field ei. which of them is correct? a、 b、 c、both of these two types of field are conservative. d、both of these two types of field are produced by electric charges.
2、in an lc circuit, the current changes as , then what is the energy stored in the capacitor? a、 b、 c、 d、
3、we can connect two inductors l1 and l2 in series to get a larger inductor. compare the total inductance l with l1 l2, which statement is true? a、l > l1 l2 b、l = l1 l2 c、l < l1 l2 d、all the 3 results are possible
4、there are some statements about the electromagnetic wave. which of them is not correct? a、the electric field and magnetic field caused by the wave is always perpendicular to each other. b、they carry energy. c、they require a medium through which to propagate. d、the wave speed depends on the properties of the medium in which they travel.
5、uniform magnetic field in cylindrical space changes as db/dt = c > 0. if a straight wire and a curved wire are both placed in the changing field as shown in the figure, which one has a greater emf in it? a、the straight wire b、the curved wire c、they have equal emf d、all the 3 cases are possible
6、the emf induced in a circuit is equal to the magnetic flux through the circuit.
7、a conductor moving in magnetic field causes a motional emf, it can be explained by the action of lorentz force.
8、the inductance of an electric device is independent of the electric current it carries.
9、the conduction current in a circuit is always continuous.
10、maxwell's equations should be modified if magnetic charges (or magnetic monopoles) are found.
11、a long solenoid is compressed to 80% of its original length (without changing the number of coils n), meanwhile the current on it changes from i to 2i. how does its magnetic energy change? from u to ________×u
12、a semicircular wire (radius r=20cm) is moving with speed v=3m/s in the plane it lays, the moving direction is perpendicular to the diameter line (dashed line in the figure). if there is a magnetic field b=0.05t as shown in figure, how much is the emf in the wire? ε = _________v.
13、microwave oven uses electromagnetic wave to heat food. suppose the space inside the oven can be treated as free space. if the electric field at point p in the oven is measured to be , then the magnetic field at point p at the same moment is b=_________t.
14、
final exam
final exam
1、when a gas undergoes an adiabatic quasi-static expansion, which of the following statements is true? a、the temperature of the gas does not change. b、no work is done by the gas. c、no energy is transferred to the gas by heat. d、the internal energy of the gas does not change.
2、about maxwell distribution of molecular speeds, which of the following statements is not true? a、it is valid for ideal gas systems in equilibrium state. b、for the same gas system, the distribution changes if temperature t changes. c、the average speed is always greater than the most probable speed. d、two gas systems have the same distribution of speeds if they are at the same temperature.
3、the second law of thermodynamics has many different statements, which of the following statements is not correct? a、100% efficiency is impossible for a heat engine. b、heat cannot transfer from cold object to hot object. c、things tend to change toward a state of greater disorder. d、the entropy of an isolated system will not decrease.
4、consider the electric field produced by an electric dipole system. when p moves along the x axis and r is much greater than the distance between two charges, how does the magnitude of electric field at p change? a、e is proportional to b、e is proportional to c、e is proportional to d、e is proportional to
5、there are statements about a conductor at electrostatic equilibrium. which of them is not correct? a、at any position inside the conductor, e= 0. b、all electrostatic charges carried by the conductor will be on the surface. c、the electric potential has the same value at any position on the conductor. d、if a conductor is connected to the ground, it carries no electrostatic charge.
6、a thin rod is uniformly charged (q, l). how much is the electric potential for point p in the figure? a、 b、 c、 d、
7、an air capacitor is connected in a circuit. if it is filled with dielectric material, how do the charge q and electric energy u stored in the capacitor change? a、both q and u increase b、both q and u decrease c、q increases and u decreases d、q decreases and u increases
8、there are some statements about hall effect. which of them is not correct? a、there may be a voltage across a current-carrying conductor if it is placed in a magnetic field. b、the charges can escape from the metal surface when they absorb enough energy. c、there are more than one force acting on the moving charges. d、hall effect can be used to distinguish p-type and n-type semiconductors.
9、when using ampere’s law, we have to know how much the current passing through the area enclosed by the chosen path is. how much is i(enclosed) in the figure? a、-i b、0 c、i d、3i
10、an electromagnetic wave travels in the free space along z direction, and the electric field at point p and time t is measured to be e= 0.06v/m (in y direction). how about the magnitude and direction of magnetic field b at point p and time t? a、 b、 c、 d、
11、about maxwell's equations and their explanation, which of the following statements is correct? a、 b、 c、magnetic field lines are always closed because there is no magnetic charge or magnetic monopole. d、the assumption of displacement current is used to explain how changing magnetic field causes electric field.
12、there are some statements about the photoelectric effect. which of them is not correct? a、the stopping voltage increases if the intensity of incoming light increases. b、the stopping voltage increases if the frequency of incoming light increases. c、an electron absorbs a photon so that it can escape from the metal surface. d、if the frequency of incoming light is lower than the cutoff frequency, there is no photocurrent.
13、the following figure shows the de broglie wave of particle 1 and particle 2. then what is the relationship about their momentums? a、 b、 c、 d、
14、according to the rules of quantum numbers of electrons inside atom, which of the following electron configuration is possible? a、 b、 c、 d、
15、for an oxygen gas system at 400k, how much is the root-mean-square speed of molecules?
16、suppose in a heat engine, the working substance is some monoatomic gas. the gas system works clockwisely around the rectangular cycle as shown in figure, how much is the efficiency? e = ____________%
17、consider a uniformly charged semi-spherical surface, where the surface density of charge is σ. how much is the electric field at the center of sphere?
18、consider a non-uniformly charged solid sphere (radius r), the volume density of charge is ρ=k(1-r/r), where k is constant and r is the distance from the center of sphere. at which position there is the maximum value of electric field? r = ___________ × r
19、a charge q=0.1c rotates in a circular orbit (r=5m) at a uniform speed v=30m/s. determine the magnetic moment of electron. μ = ______________ (si units)
20、uniform magnetic field exists only in a cylindrical space with radius r=4, and it changes as db/dt = 3. how much is the induced electric field at point p with distance r=10 from the central axis of cylinder? (si units) e = ______________.
21、a hydrogen atom jumps from its 3rd excited state to another state of lower energy and emits a photon. what is the minimum wavelength of that photon? λ = __________ nm