Q: A generator coil has 100 turns, an area of $$0.02\ \mathrm{m}^2$$, rotates in a $$0.5\ \mathrm{T}$$ field at $$60\ \mathrm{Hz}. $$What is the peak emf produced? Use $$E_0 = $$NAB\omega$$ and $$\omega = 2\pi f$$.

$$E_0 = 100$$ \times 0.02 \times 0.5 \times 2\pi \times 60 = 377\ \mathrm{V}$$

Question 1

Which of the following best describes the main difference between the devices shown in the two images above?

Accepted Answer

The first device converts electrical energy into mechanical energy, while the second device converts mechanical energy into electrical energy.

Question 2

In the first image, what is the role of the commutator in the electric motor?

Accepted Answer

It reverses the current direction in the coil every half turn to keep the torque in the same direction.

Question 3

According to Faraday’s Law, what is required to induce an emf in the coil of the generator shown in the second image?

Accepted Answer

A changing magnetic flux through the coil.

Question 4

If the coil in the generator (second image) is rotated faster, what happens to the induced emf?

Accepted Answer

The induced emf increases.

Question 5

Which equation correctly gives the maximum emf generated by a coil of area $$A$$, $$N$$ turns, in a magnetic field $$B$$, rotating with angular velocity $$\omega$$?

Accepted Answer

$$E_0 = $$NAB\omega$$

Question 6

In the electric motor (first image), what is the direction of the force on the top segment of the coil due to the magnetic field?

Accepted Answer

Out of the page (toward the observer)

Question 7

Which law explains why the current in the generator coil (second image) changes direction as the coil rotates?

Accepted Answer

Lenz’s Law

Question 8

If the magnetic field in the generator (second image) is doubled while keeping all other factors constant, what happens to the peak emf?

Accepted Answer

It doubles.

Question 9

Which of the following best describes the energy transformation in the electric motor (first image)?

Accepted Answer

Electrical energy is converted to mechanical energy.

Question 10

A generator coil has 100 turns, an area of $$0.02\ \mathrm{m}^2$$, rotates in a $$0.5\ \mathrm{T}$$ field at $$60\ \mathrm{Hz}. $$What is the peak emf produced? Use $$E_0 = $$NAB\omega$$ and $$\omega = 2\pi f$$.

Accepted Answer

$$E_0 = 100$$ 	imes 0.02 	imes 0.5 	imes 2\pi 	imes 60 = 377\ \mathrm{V}$$

Question 11

Which of the following statements is true about the similarities between an electric motor and a generator?

Accepted Answer

Both devices use coils of wire and magnetic fields to transfer energy.

Question 12

If the direction of rotation of the coil in the generator (second image) is reversed, what happens to the direction of the induced current?

Accepted Answer

The direction of the induced current reverses.

Question 13

Which of the following best explains why a generator produces alternating current (AC)?

Accepted Answer

The coil rotates in a magnetic field, causing the direction of the induced emf to reverse every half turn.

Question 14

In the electric motor (first image), what would happen if the magnetic field strength is increased while keeping the current constant?

Accepted Answer

The torque on the coil increases.

Electromagnetic Induction and Faraday’s Law: Study Notes

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