Question 1

A credit card reader at a gas station requires you to remove your card quickly rather than hold it motionless in the slot. Which principle explains why the card must be moved for the reader to function?

Accepted Answer

The card reader uses Faraday's law, which states that a changing magnetic flux induces an emf.

Question 2

A coil of wire is connected to a galvanometer. When a magnet is moved toward or away from the coil, the meter shows a current. What is the cause of this induced current?

Accepted Answer

The magnet's motion changes the magnetic flux through the coil, inducing an emf.

Question 3

Which equation correctly expresses Faraday's law for the induced emf in a single closed loop?

Accepted Answer

$$\varepsilon = -\frac{d\Phi_B}{dt}$$

Question 4

A coil with $$N$$ turns is placed in a changing magnetic field. If the magnetic flux through each turn changes at the same rate, what is the total induced emf?

Accepted Answer

$$\varepsilon = -N \frac{d\Phi_B}{dt}$$

Question 5

According to Lenz's law, what is the direction of the induced current in a loop when the magnetic flux through the loop is increasing?

Accepted Answer

The induced current creates a magnetic field that opposes the increase in flux.

Question 6

A conducting rod moves perpendicular to a uniform magnetic field. Which equation gives the motional emf induced in the rod?

Accepted Answer

$$\varepsilon = vBL$$

Question 7

A metal ring is placed between the poles of large magnets. The magnetic field is decreasing steadily. What is the direction of the induced current as viewed from the south pole?

Accepted Answer

Counterclockwise

Question 8

Which of the following is NOT a consequence of Maxwell's equations?

Accepted Answer

Magnetic monopoles exist in nature.

Question 9

A parallel-plate capacitor is being charged. The displacement current density $$j_D in $$the air space between the plates is given by:

Accepted Answer

$$j_D = \$$varepsilon_0$$ \frac{dE}{dt}$$

Question 10

Which phenomenon is responsible for the levitation of a superconductor above a magnet?

Accepted Answer

The Meissner effect, which expels all magnetic flux from the superconductor.

Question 11

A rectangular loop of wire is pulled out of a region of uniform magnetic field at constant speed. What is the direction of the force exerted by the magnetic field on the loop?

Accepted Answer

Opposite to the direction of motion (left)

Question 12

Which equation represents Gauss's law for electric fields?

Accepted Answer

$$\oint \vec{E} \cdot d\vec{A} = \frac{Q_{encl}}{\$$varepsilon_0$$}$$

Question 13

A coil is rotated from a position perpendicular to the Earth's magnetic field to parallel in 0.050 s. If the area is $$13\ 	ext{cm}^2$$ and the field is $$7.0 	imes 10$$^{-5}$$\ 	ext{T}$$, what is the average induced emf in the coil with 210 turns?

Accepted Answer

$$3.8 	imes 10$$^{-4}$$\ 	ext{V}$$

Question 14

Which of the following best describes eddy currents?

Accepted Answer

Currents induced in a metal when it moves through a magnetic field or is in a changing magnetic field.

Question 15

A circular loop of wire with radius $$0.0450\ 	ext{m}$$ and resistance $$0.161\ \Omega is in a $$region where the magnetic field is decreasing at $$-0.649\ 	ext{T/s}. $$What is the rate at which electrical energy is dissipated?

Accepted Answer

$$1.06 	imes 10$$^{-4}$$\ 	ext{W}$$

Question 16

Which of the following statements about magnetic flux is correct?

Accepted Answer

Magnetic flux is maximum when the surface is face-on to the magnetic field.

Question 17

Which equation represents the motional emf for a rod of length $$L$$ moving at speed $$v$$ perpendicular to a uniform magnetic field $$B$$?

Accepted Answer

$$\varepsilon = vBL$$

Question 18

Which of the following is a real-world application of electromagnetic induction?

Accepted Answer

Metal detectors at airport security checkpoints

Electromagnetic Induction and Related Phenomena: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard