What will be the direction of the drift velocity of electrons change w

1.One reason why we know that magnetic fields are not the same as electric fields is because the force exerted on a charge +q 选项： A、is in opposite directions in electric and magnetic fields. B、is in the same direction in electric and magnetic fields. C、is parallel to a magnetic field and perpendicular to an electric field. D、is parallel to an electric field and perpendicular to a magnetic field. E、is zero in both if the charge is not moving.

2.A charged particle moves through a region of space that has both a uniform electric field and a uniform magnetic field. In order for the particle to move through this region at a constant velocity,选项： A: the electric and magnetic fields must point in the same direction.; B:the electric and magnetic fields must point in opposite directions.; C:the electric and magnetic fields must point in perpendicular directions.; D:The answer depends on the sign of the particle’s electric charge.

3.When a charged particle moves through a magnetic field, the direction of the magnetic force on the particle at a certain point is选项： A:in the direction of the magnetic field at that point.; B:opposite to the direction of the magnetic field at that point.; C:perpendicular to the magnetic field at that point.; D:none of the above; E:The answer depends on the sign of the particle’s electric charge.

4.A proton is released from rest at the origin in a uniform electric field in the positive \(x\) direction with magnitude \(850\,N/C\). What is the change in the electric potential energy of the proton-field system when the proton travels to \(x = 2.50\,m\)?

5.In a p-n junction, the direction of the built-in electric field is from 选项： A:n to p, and the electric field is uniform within the junction.; B:p to n, and the electric field is uniform within the junction.; C:n to p, and the electric field is non-uniform within the junction.; D:p to n, and the electric field is non-uniform within the junction.

6.In a p-n junction, the direction of the built-in electric field is from 选项： A、n to p, and the electric field is uniform within the junction. B、p to n, and the electric field is uniform within the junction. C、n to p, and the electric field is non-uniform within the junction. D、p to n, and the electric field is non-uniform within the junction.

7.The free-space polarization of an antenna is determined by ________.选项： A:the orientation of its electric field ; B: the orientation of its magnetic field; C: the orientation of its electric and magnetic fields ; D: the radiation direction

8.In a certain region of space, the electric potential is +2 V everywhere along the x axis. From this information, you can conclude that the x component of the electric field in this region is: A: zero. B: in the positive x direction. C: in the negative x direction.

9.The Biot-Savart Law is used to（）选项： A:determine the electric field created by an electric current B:determine the force field created by an electric current C:determine the magnetic field created by an electric current D:determine the magnetic field created by individual point charges E:determine the electric field created by individual point charges

10.Electric field vector vibrates in only one plane and perpendicular to the direction of propagation in what light ( )选项： A:plane polarised B:unpolarised C:both plane polarised & unpolarised D:neither plane polarised & nor unpolarised

11.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 ( )选项： A:is negative. B:is positive. C:increases. D:decreases. E:electric fields cannot do work.

12.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 ( ) 选项： A、is negative. B、is positive. C、increases. D、decreases. E、electric fields cannot do work.

13.A magnetic field exerts a non-zero force on a particle. Which of the following must be true? ( ) 选项： A、The particle is negatively charged. B、The particle is stationary. C、The direction of the force is perpendicular to both the velocity of the particle and the magnetic field. D、The direction of the force is parallel to the magnetic field but perpendicular to the motion of the particle. E、The direction of the force is perpendicular to the magnetic field but parallel to the motion of the particle.

14.For the sources of electric and magnetic fields, which of the following statements is incorrect?选项： A:Any time-varying magnetic field gives rise to an electric field.; B:Any time-varying electric field gives rise to a magnetic field.; C:Any current gives rise to a magnetic field.; D:Any charge gives rise to a magnetic field.

15.(2016.24)

A proton moves with constant non-zero velocity in a region of space that has a uniform magnetic field directed into the plane of the page. The proton moves directly up the plane of the page. What is the direction of the electric field in this region of space? Ignore gravity.

选项： A:

To the left

B:

To the right

C:

Down the plane of the page

D:

Up the plane of the page

E:

There is no electric field necessary

16.The electric field across the pn junction is found by integrating the density of electrons

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

18.The electric potential at x=5.00m and y=3.00m is 120V and the electric potential at x=7.50m and y=8.00m is 180V. The electric field is along the axis between the two points and is uniform. What is the magnitude of the Electric Field in N/C in this region?______ In a uniform E field the relationship between the field magnitude and change in potential is ΔV=−Ed. Use the pythagorean theorem to find the separation between the two points, and the potential difference of 60V.

19.In order that an electric current can be produced in a conductor, an electric field must be built in it.

20.3) The electric potential at x = 3.00 m is 120 V, and the electric potential at x=5.00 m is 190 V. What is the x component of the electric field in this region, assuming the field is uniform (in N/C)? 选项： A、140 B、-140 C、35 D、-35 E、75