Question

3/ Imagine a wire sticking out of center of a clock. If there is current in the wire that is traveling out of the face of the clock, towards you, what is the direction of the magnetic field created by the current?

Select one:

a. Clockwise

b. Counter-clockwise

c. Upward (from the 6 to the 12)

d. Downward (from the 12 to the 6)

e. In the same direction as the current (toward you)

4/ A magnetic field points to the right across your computer screen. If a positive charge is moving to the left across your computer screen, what is the direction of the force on the charge from the magnetic field?

Select one:

a. Up the screen

b. Down the screen

c. To the right

d. To the left

e. Out of the screen

f. Into the screen

g. There is no force

5/ A current moving in a long, straight wire creates a magnetic field. How does the magnetic field change if the current were moving in the opposite direction through the wire?

Select one:

a. There would be no magnetic field.

b. The magnetic field changes direction also.

c. The magnetic field becomes stronger.

d. The magnetic field becomes weaker.

e. The magnetic field would not change.

6/ At the Large Hadron Collider at CERN, protons travel at nearly the speed of light in a large circle. The protons are pushed in this circle by magnetic fields. What does the direction of the magnetic fields have to be so that the protons travel clockwise when looking at their path from space?

Select one:

a. The magnetic field points clockwise

b. The magnetic field points counterclockwise

c. The magnetic field points into the ground

d. The magnetic field points out of the ground

e. The magnetic field points towards the north.

7/ Which of the follow can the magnetic force can change about a moving charged particle? Select all correct answers.

Select one or more:

a. The speed of the particle

b. The direction the particle moves in

c. The charge of the particle

d. The mass of the particle

e. The velocity of the particle

8/ In a region of space, a magnetic field points north and an electric field points west. An electron moving at a certain velocity feels no net force when traveling through this region. If a proton moves with exactly the same velocity as the electron (speed and direction), what can you say about the force on the proton?

Select one:

a. Both the electric force and the magnetic force will change direction, so there will also be no net force on the proton.

b. The magnetic force on the proton will become larger than the electric force - so the proton will feel a net force.

c. The magnetic force on the proton will become smaller than the electric force - so the proton will feel a net force.

d. Only the magnetic force will change direction, so the proton will feel a force.

e. Only the electric force will change direction, so the proton will feel a force.

9/ A current carrying wire in a magnetic field feels an eight Newton force to the right. How does the force change if the length of wire inside the field is reduced by half?

Select one:

a. The magnitude of the force becomes two Newtons. The direction does not change.

b. The force does not change.

c. The magnitude of the force becomes four Newtons. The direction does not change.

d. The magnitude of the force becomes sixteen Newtons. The direction does not change.

e. The force stays the same magnitude, but changes direction.

10/ Coil A contains 8 loops of wire and has an area of 4 square meters. Coil B has 16 loops of wire and has an area of 2 square meters. If the coils have the same current and are arranged the same inside a magnetic field, which coil experiences a larger torque?

Select one:

a. Coil A because it has a larger area

b. Coil A because it has fewer loops of wire.

c. Coil B because it has a smaller area.

d. Coil B because it has more loops of wire.

e. They experience the same torque.

Answer 1

3) According to Right hand thumb's rule the direction of the magnetic field will be counter-clockwise so option b is correct.

4) Magnetic force F on the charged particle q moving with velocity v in the presence of magnetic field B can be expressed as

F=q (v x B).......(1)

The bold characters are vectors. As per the definition of cross product the direction of force must be perpendicular to the plane containing v and B. As both are moving on the plane of screen so the direction of the force must be out of the screen. Hence, option e is correct.

5) Since, the magnitude of the current remains same but its direction is reversed so the strength of the magnetic field will remain the same as per right hand thumb rule the direction of the magnetic field will be reversed. So option b is correct.

6) Option c is correct. Magnetic field should point into the ground.

7) As shown in Eq. (1), the magnetic force can change the speed its magnitude and the direction of the motion and the velocity of the particle. Hence, option a), b) and e) are correct.

8) The expression of the electric force F=qE.....(a) and the expression of the magnetic force is F=q (v x B). Clearly, q appears in the expression of both the charges so if the nature of charges, the direction of F will also change. Hence, both the force will change their directions if the electrons are replaced from protons. Sine the their magnitude will remain the same so they will cancel each other. So option a) is correct. There will be no net force on proton.

9) The magnitude of Magnetic force can also be expressed as

F=I LB.....(2)

Here, L is the length of the current carrying wire and it is directly proportional to the length. So if the length is reduced by half the magnitude of the magnetic force will also be reduced by half and will become 4 Newtons. Additionally, length is a scalar quantity so it will not impact its direction. Hence, option c) is correct.

10) The expression of torque can be given as

tau =n I A B sin theta

Here, n and A are the number of turns and the area, respectively. As we are going from one coli to second coil the number of turns are two times but the area is halfed so they are nullifying each others effect. Hence the net torque will remain the same. Option (e) is correct.