A circular loop of wire with a radius of 5 cm rotates clockwise at a constant angular velocity through a magnetic field 

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A circular loop of wire with a radius of 5 cm rotates clockwise at a constant angular velocity through a magnetic field B = 5 T. The plane of the loop goes from being perpendicular to the field to being at a 45º angle with the field in 0.25 s. The average emf induced in the loop will be

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A charge +Q is fixed in position as a small charge +q is brought near it and released from rest. Which best describes the magnitude of the velocity of the charge +q as r, the distance between the charges increases? ( )
A:The magnitude of the velocity will increase, but its rate of increase will decrease.
B:The magnitude of the velocity will remain constant.
C:The magnitude of velocity will increase, but its rate of decrease will increase.
D:The magnitude of the velocity will increase, and its rate of increase will also increase.
E:The magnitude of the velocity will decrease, and its rate of decrease will also decrease.
答案: The magnitude of the velocity will increase, but its rate of increase will decrease.

The motion of large bodies at great distances is governed primarily by gravity and not by the electrostatic force because ( )
A:the majority of matter is electrically neutral
B:the electrostatic force is canceled out by the magnetic force
C:the electrostatic force is felt only over short distances
D:of the relative scarcity of antiparticles
E:gravity is a much stronger force than the electrostatic force
答案: the majority of matter is electrically neutral

An object with a charge of –2q feels a force of F when put at a point P in an electric field. In terms of F and q, the strength of the electric field at this point is ( ).
A:

B:

C:2qF
D:

E:

答案:

All of the following are true about Gauss’ law EXCEPT ( )
A:Gauss’ law is useful when the electric field is perpendicular to the differential area.
B:Gauss’ law refers to the flux through a closed surface.
C:A rectangle is an example of a Gaussian surface.
D:Gauss’ law states that the flux through the closed surface is proportional to the total charge within the surface.
E:Gauss’ law is useful when the electric field is zero.
答案: A rectangle is an example of a Gaussian surface.

Based on Gauss’ Law, which of the following affects the electric flux through a Gaussian surface?( )
A:a charge moving with a constant velocity outside the surface
B:a stationary electric charge outside the surface
C:a magnetic monopole enclosed by the surface
D:a stationary electric charge enclosed by the surface
E:a magnetic dipole outside of the surface
答案: a stationary electric charge enclosed by the surface

Which of the following pairs of charge distributions and Gaussian surfaces are correctly paired such that the Gaussian surface can be used to find the electric field associated with that charge distribution?( )
A:plane and cylinder
B:infinite line and rectangle
C:plane and rectangle
D:plane and sphere
E:infinite line and sphere
答案: plane and cylinder

If the electric field does positive work on a negative charge as the charge undergoes a displacement from point A to point B within an electric field, then the electrical potential energy ( )
A:electric fields cannot do work.
B:decreases.
C:increases.
D:is positive.
E:is negative.
答案: decreases.

The negative derivative of electric potential with respect to radius is equal to （ ）
A:charge
B:electric force
C:electric field
D:capacitance
E:potential energy
答案: electric field

The potential difference due to a finite rod along the x-axis is given by the equation V(x) = C[ln(x + L) – ln(x)], where C and L are constants. What is the electric field due to this rod? （ ）
A:

B:

C:

D:

E:

答案:

Point A is a distance L to the left of a charge Q. Point B is a distance 3L to the left of point A. If the electric field at point A due to charge Q is E, what is the electric field at point B?

A:3E
B:E/3
C:E/16
D:E/9
E:E
答案: E/16

A:

B:

C:

D:

E:

答案:

Two solid spheres, both of radius 5 cm, carry identical total charges of 2 nC. Sphere A is a good conductor. Sphere B is an insulator, and its charge is distributed uniformly throughout its volume. How do the magnitudes of the electric fields they separately create at a radial distance of 6 cm compare?

A:

B:

C:

D:

E:

答案:

A:

B:

C:

D:

E:

答案:

A:

B:

C:

D:

E:

答案:

Two charged conducting spheres are touched together. Charge flows between them until which of the following is the same for both spheres?( )
A:electric field at the surface
B:electric field at the center
C:total energy
D:electric potential
E:total charge
答案: electric potential

An uncharged metal sphere is placed within a uniform electric field. Which of the following is true about the net force and torque on the sphere? （ ）
A:The net force and net torque are both zero.
B:The net force is against the direction of the field, and the net torque is against the direction of the field.
C:The net force is zero and the net torque is in the direction of the field.
D:The net force is in the direction of the field, and the net torque is in the direction of the field.
E:The net force is zero and the net torque is against the direction of the field.
答案: The net force and net torque are both zero.

A solid sphere consists of a metal core, a non-conducting middle shell, and a metal outer shell. If a positive charge is placed on the core, where in the sphere will a net positive charge be found? ( )
A:evenly distributed throughout the two metal regions
B:on the outer surface of the core
C:on the outer surface of the outer shell
D:evenly distributed throughout the core
E:on both the outer surface of the core and the outer surface of the outer shell
答案: on both the outer surface of the core and the outer surface of the outer shell

Two conducting spheres of different radii each carry a charge +Q. Which of the following occurs when the two spheres are touched together? ( )
A:Positive charge flows from the larger sphere to the smaller sphere until the electric field at the surface of each sphere is the same.
B:No charge flows.
C:Positive charge flows from the smaller sphere to the larger sphere until the electric field at the surface of each sphere is the same.
D:Positive charge flows from the larger sphere to the smaller sphere until the electric potential at the surface of each sphere is the same.
E:Positive charge flows from the smaller sphere to the larger sphere until the electric potential at the surface of each sphere is the same.
答案: Positive charge flows from the smaller sphere to the larger sphere until the electric potential at the surface of each sphere is the same.

Three identical metal spheres are mounted on insulating stands. Initially, sphere A has a net charge of q and spheres B and C are uncharged. Sphere A is touched to sphere B and removed. Then sphere A is touched to sphere C and removed. What is the final charge on sphere A? ( )
A:q
B:q/6
C:q/3
D:q/4
E:q/2
答案: q/4

A parallel-plate capacitor has capacitance C. A second parallel-plate capacitor has plates with twice the area and half the separation. The capacitance of this second capacitor is most nearly （ ）
A:C/4
B:C/2
C:C
D:4C
E:2C
答案: 4C

All of the following are true about spherical capacitors EXCEPT ( )
A:The electric field outside the outer sphere is zero
B:The electric field between the two spheres is determined only by the charge on the outer sphere
C:The potential difference between the two spheres is the negative integral of the electric field
D:The electric field points radially towards the center of the spheres
E:The capacitance is equal to the charge divided by the potential difference
答案: The electric field between the two spheres is determined only by the charge on the outer sphere

A battery is attached to several different capacitors connected in parallel. Which of the following statements is true?（ ）
A:The potential differences across the capacitors are the same only if the capacitances are the same.
B:The capacitor with the smallest capacitance carries the largest charge.
C:The potential difference across each capacitor is the same, and the equivalent capacitance is greater than any of the capacitors in the group.
D:All capacitors have the same charge, and the equivalent capacitance is greater than the capacitance of any of the capacitors in the group.
E:The capacitor with the largest capacitance carries the smallest charge.
答案: The potential difference across each capacitor is the same, and the equivalent capacitance is greater than any of the capacitors in the group.

A parallel-plate capacitor is connected to a battery. What happens to the stored energy if the plate separation is doubled while the capacitor remains connected to the battery?（ ）
A:It increases by a factor of 4.
B:It remains the same.
C:It is doubled.
D:It decreases by a factor of 4.
E:It decreases by a factor of 2.
答案: It decreases by a factor of 2.

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