Test 2 Questions

Question 1

A charged particle moves in a straight line through a certain region of space. The magnetic field in that region

(a) has a magnitude of zero
(b) has a zero component perpendicular to the particle’s velocity
(c) has a zero component parallel to the particle’s velocity

Answer 1

(b). The force that a magnetic field exerts on a charged particle moving through it is given by F = qvB sin θ = qvB , where B is the component of the field perpendicular to the particle’s velocity. Since the particle moves in a straight line, the magnetic force (and hence B , since qv ≠ 0) must be zero.

Question 2

The north-pole end of a bar magnet is held near a stationary positively charged piece of plastic. Is the plastic

(a) attracted
(b) repelled
(c) unaffected by the magnet

Answer 2

(c). The magnetic force exerted by a magnetic field on a charge is proportional to the charge’s velocity relative to the field. If the charge is stationary, as in this situation, there is no magnetic force.

Question 3

All magnetic fields originate in

(a) iron
(b) permanent magnets
(c) magnetic domains
(d) moving electric charges

Answer 3

(d) moving electric charges

Question 4

Magnetic fields do not interact with

(a) stationary electric charges
(b) moving electric charges
(c) stationary permanent magnets
(d) moving permanent magnets

Answer 4

(a) stationary electric charges

Question 5

As a charged particle moves freely in a circular path in the presence of a constant magnetic field applied perpendicular to the particle’s velocity, its kinetic energy

(a) remains constant
(b) increases
(c) decreases.

Answer 5

(a). The magnetic force acting on the particle is always perpendicular to the velocity of the particle, and hence to the displacement the particle is undergoing. Under these conditions, the force does no work on the particle and the particle’s
kinetic energy remains constant.

Question 6

Two charged particles are projected into a region in which a magnetic field is perpendicular to their velocities. After they enter the magnetic field, you can conclude that

(a) the charges are deflected in opposite directions
(b) the charges continue to move in a straight line
(c) the charges move in circular paths
(d) the charges move in circular paths but in opposite directions.

Answer 6

(c). Anytime the velocity of a charged particle is perpendicular to the magnetic field, it will follow a circular path. The two particles will move in opposite directions around their circular paths if their charges have opposite signs, but their charges are unknown so (d) is not an
acceptable answer.

Question 7

Can you set a resting electron into motion with a magnetic field? With an electric field?

Answer 7

The magnetic force on the electron is zero since v=0 (F=qvBsinΘ). An electric field will accelerate the electron.

Question 8

Which one of the following statements concerning the magnetic force on a charged particle in a magnetic field is true?
(a) It is a maximum if the particle is stationary.
(b) It is zero if the particle moves perpendicular to the field.
(c) It is a maximum if the particle moves parallel to the field.
(d) It acts in the direction of motion for a positively charged particle.
(e) It depends on the component of the particle’s velocity that is perpendicular
to the field.

Answer 8

(e) It depends on the component of the particle’s velocity that is perpendicular
to the field.

Question 9

A charged particle is moving in a uniform, constant magnetic field. Which one of the following statements concerning the magnetic force exerted on the particle is false?

(a) It does no work on the particle.
(b) It increases the speed of the particle.
(c) It changes the velocity of the particle.
(d) It can act only on a particle in motion.
(e) It does not change the kinetic energy of the particle.

Answer 9

(b) It increases the speed of the particle.

Question 10

The force on a wire carrying 25 A is a maximum of 4.14 N when placed between the pole faces of a magnet, If the pole faces are 22 cm in diameter, what is the approximate strength of the magnetic field?

Answer 10

A maximum F means sinΘ=1, or Θ=90o Fmax=IlB or B=Fmax/Il=(4.14N)/(25A)(0.22m)=0.753 T

Question 11

The right-hand rule for the direction of the force on a charged particle in a magnetic field applies:

(a) only to positive charges
(b) only to negative charges
(c) to both positive and negative charges
(d) only when the particle is moving parallel to field.

Answer 11

(a) only to positive charges

Question 12

A charge particle moves perpendicularly through a magnetic field. The effect of the field is to change the particle’s

(a) charge
(b) mass
(c) velocity
(d) energy

Answer 12

(c) velocity

Question 13

The magnetic field a distance d from a long, straight wire is proportional to

(a) d
(b) d2
(c) 1/d2
(d) 1/d

Answer 13

(d) 1/d

Question 14

Two loops carry equal currents I in the same direction. The loops are held in the positions shown in the figure and are then released. Which one of the following statements correctly describes the subsequent behavior of the loops?
(a) Both loops move to the left.
(b) The loops remain in the positions shown.
(c) The top loop moves to the right; the bottom loop
moves to the right.
(d) The loops repel each other.
(e) The loops attract each other.

Answer 14

(e) The loops attract each other.

Question 15

Two long, straight wires are perpendicular to the plane of the paper as shown in the drawing. Each wire carries a current of magnitude I. The currents are directed out of the paper toward you. Which one of the following expressions correctly gives the magnitude of the total magnetic field at the origin of the x,y coordinate system?

(a) μoI/2d
(b) μoI/2πd
(c) μoI/√2πd
(d) μoI/√2d
(e) μoI/d

Answer 15

(c) μoI/√2πd

Question 16

When a ferromagnetic substance is inserted in a current-carrying solenoid, the magnetic field is

(a) slightly decreased
(b) greatly decreased
(c) slightly increased
(d) greatly increased

Answer 16

(d) greatly increased

Question 17

Electromotive force (emf) is most closely related to

(a) electric field
(b) magnetic field
(c) potential difference
(d) mechanical force

Answer 17

(c) potential difference

Question 18

A bar magnet is passed through a coil of wire. The induced current is greater when

(a) the magnet moves slowly, so that it is inside the coil for a long time
(b) the magnet moves fast, so that it is inside the coil for a short time
(c) the north pole of the magnet enters the coil first
(d) the south pole of the magnet enters the coil first

Answer 18

(b) the magnet moves fast, so that it is inside the coil for a short time

Question 19

The magnetic flux through a wire loop in a magnetic field B does not depend on

(a) the area of the loop
(b) the shape of the loop
(c) the angle between the plane of the loop and the direction of B
(d) the magnitude B of the field

Answer 19

(b) the shape of the loop

Question 20

A wire loop is moved parallel to a uniform magnetic field. The induced emf in the loop

(a) depends on the area of the loop
(b) depends on the shape of the loop
(c) depends on the magnitude of the field
(d) is 0

Answer 20

(d) is 0

Question 21

Two conducting loops carry equal currents I in the same direction as shown in the figure. If the current in the upper loop suddenly drops to zero, what will happen to the current in the bottom loop according to Lenz’s law?

(a) The current will decrease.
(b) The current will increase.
(c) The current will not change.
(d) The current will also drop to zero.
(e) The current will reverse its direction.

Answer 21

(b) The current will increase.

Question 22

Alternating current is the secondary coil of a transformer is induced by

(a) a varying electric field
(b) a varying magnetic field
(c) the iron core of the transformer
(d) motion of the primary

Answer 22

(b) a varying magnetic field

Question 23

In a vacuum, the speed of an electromagnetic wave

(a) depends on its frequency
(b) depends on its wavelength
(c) depends on its electric and magnetic fields
(d) is a universal constant

Answer 23

(d) is a universal constant

Question 24

Which one of the following statements concerning electromagnetic waves is false?

(a) Electromagnetic waves are longitudinal waves.
(b) Electromagnetic waves transfer energy through space.
(c) The existence of electromagnetic waves was predicted by Maxwell.
(d) Electromagnetic waves can propagate through a material substance. (e) Electromagnetic waves do not require a physical medium

Answer 24

(a) Electromagnetic waves are longitudinal waves.

Question 25

Which one of the following will not generate electromagnetic waves or pulses?

(a) a steady direct current
(b) an accelerating electron
(c) a proton in simple harmonic motion
(d) an alternating current
(e) charged particles traveling in a circular path in a mass spectrometer

Answer 25

(a) a steady direct current

Question 26

Complete the following sentence: When electrons from a heated filament accelerate through vacuum toward a positive plate,

(a) only an electric field will be produced.
(b) only a magnetic field will be produced.
(c) electromagnetic waves will be produced.
(d) longitudinal waves will be produced.
(e) neither electric nor magnetic fields will be produced.

Answer 26

(c) electromagnetic waves will be produced.

Question 27

Which one of the following types of wave is intrinsically different from the other four?

(a) radio waves
(b) gamma rays
(c) visible light
(d) sound waves
(e) ultraviolet radiation

Answer 27

(d) sound waves

Question 28

Which one of the following statements concerning electromagnetic waves is false?

(a) Electromagnetic waves carry energy.
(b) X-rays have longer wavelengths than radio waves.
(c) In vacuum, all electromagnetic waves travel at the same speed.
(d) Lower frequency electromagnetic waves can be produced by oscillating circuits.
(e) They consist of mutually perpendicular electric and magnetic fields that oscillate perpendicular to the direction of propagation.

Answer 28

(b) X-rays have longer wavelengths than radio waves.

Question 29

Complete the following sentence: The various colors of visible light differ in

(a) frequency only.
(b) frequency and wavelength.
(c) wavelength only.
(d) frequency and their speed in a vacuum. (e) their speeds in a vacuum.

Answer 29

(b) frequency and wavelength.