Question 1

Which of the following best explains why no current is induced in a coil when a magnet is held stationary near it, as shown in the first image?

Accepted Answer

There is no change in magnetic flux through the coil.

Question 2

According to Faraday’s law, what is the mathematical expression for the induced emf in a coil with N turns when the magnetic flux changes with time?

Accepted Answer

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

Question 3

A magnet is moved toward a coil, causing the ammeter to deflect. What is the physical principle responsible for the induced current?

Accepted Answer

The change in magnetic flux through the coil.

Question 4

In the experiment where a current-carrying coil is moved relative to a stationary coil, what is observed and why?

Accepted Answer

A current is induced in the stationary coil due to the changing magnetic field from the moving coil.

Question 5

Which law determines the direction of the induced current in a loop when the magnetic flux changes?

Accepted Answer

Lenz's Law

Question 6

A conducting bar moves to the right through a uniform magnetic field directed into the page. What is the expression for the induced emf across the ends of the bar?

Accepted Answer

$$\varepsilon = Bv\ell$$

Question 7

If the area of a loop in a magnetic field changes with time, which of the following correctly describes the induced emf?

Accepted Answer

$$\varepsilon = -\frac{d}{dt}(BA)$$

Question 8

A loop of wire rotates in a uniform magnetic field. What is the expression for the instantaneous induced emf if the loop has N turns and area A?

Accepted Answer

$$\varepsilon = NAB\omega \sin(\omega t)$$

Question 9

Which of the following statements about eddy currents is correct?

Accepted Answer

Eddy currents are induced in bulk metal moving through a magnetic field and can cause energy losses.

Question 10

A generator converts mechanical energy to electrical energy. What is the key physical process that enables this conversion?

Accepted Answer

A loop is rotated in a magnetic field, causing the magnetic flux through the loop to change.

Question 11

Which of the following is NOT a way to induce an emf in a loop according to Faraday’s law?

Accepted Answer

Keeping the magnetic flux constant.

Question 12

What is the physical significance of the negative sign in Faraday’s law $$\varepsilon = -\frac{d\Phi_B}{dt}$$?

Accepted Answer

It shows that the induced emf opposes the change in magnetic flux, as described by Lenz’s law.

Question 13

A ground fault indicator (GFI) uses Faraday’s law to protect users. What triggers the circuit breaker in a GFI?

Accepted Answer

A change in the return current in one wire, causing a nonzero magnetic flux.

Question 14

In a motor, what is the role of the back emf?

Accepted Answer

It reduces the current supplied to the coil as the rotational speed increases.

Question 15

Which of Maxwell’s equations describes the relationship between a changing magnetic field and the induced electric field?

Accepted Answer

$$\int \vec{E} \cdot d\vec{l} = -\frac{d\Phi_B}{dt}$$

Question 16

A bar of length $$\ell$$ moves with velocity $$v$$ perpendicular to a uniform magnetic field $$B. $$What is the potential difference between the ends of the bar?

Accepted Answer

$$\Delta V = B \ell v$$

Question 17

Which of the following best describes the induced electric field generated by a changing magnetic field?

Accepted Answer

It is a nonconservative field, unlike the field from stationary charges.

Question 18

A pickup coil in an electric guitar uses Faraday’s law. What causes the induced emf in the coil?

Accepted Answer

The vibrating string produces a changing magnetic flux through the coil.

Question 19

Which of the following is a consequence of energy conservation in electromagnetic induction?

Accepted Answer

The induced current always opposes the change in magnetic flux.

Electromagnetic Induction and Faraday’s Law: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard