Q: A wire of length $$L = 22 cm is in a $$region of uniform magnetic field $$B = 0.031 T$$, and forms a $$45^\circ$$ angle with the field. If the current in the wire is $$I = 0.046 A$, $$ what is the magnitude of the force on the wire?

$$F = ILB \sin \theta = 0.046 \times 0.22 \times 0.031 \times \sin 45^\circ$$

Question 1

A proton moves with velocity $$\vec{v}$$ perpendicular to a uniform magnetic field $$\vec{B}. $$What is the magnitude of the force acting on the proton?

Accepted Answer

$$F = qvB$$

Question 2

A circular loop of radius $$R$$ carries a steady current $$I. $$What is the magnitude of the magnetic field at the center of the loop?

Accepted Answer

$$B = \dfrac{\mu_0$ I}{2R}$$

Question 3

A wire of length $$L = 22 cm is in a $$region of uniform magnetic field $$B = 0.031 T$$, and forms a $$45^\circ$$ angle with the field. If the current in the wire is $$I = 0.046 A$, $$ what is the magnitude of the force on the wire?

Accepted Answer

$$F = ILB \sin 	heta = 0.046 	imes 0.22 	imes 0.031 	imes \sin 45^\circ$$

Question 4

Which of the following best describes the direction of the force on a negatively charged particle moving to the right in a uniform magnetic field directed into the page?

Accepted Answer

Downward, toward the bottom of the page

Question 5

A solenoid has length $$L$$, $$N$$ turns, and cross-sectional area $$A. $$What is the inductance $$L of $$the solenoid?

Accepted Answer

$$L = \dfrac{\mu_0$ N^2$ A}{L}$$

Question 6

An LC circuit has an inductor of $$0.80 H $$and a capacitor of $$2.0 \muF. $$What is the angular frequency $$\omega of $$oscillation?

Accepted Answer

$$\omega = \dfrac{1}{\sqrt{LC}}$$

Question 7

A conducting bar and a U-shaped conducting track form a loop in a uniform magnetic field pointing into the page. If the bar is given a rightward velocity $$v$$, what is the direction of the induced current in the loop?

Accepted Answer

Counterclockwise, as seen from above

Question 8

Which of the following is the correct expression for the energy stored in an inductor with inductance $$L$$ and current $$I$$?

Accepted Answer

$$U = \dfrac{1}{2} L I^2$

Question 9

A transformer has 100 turns in the primary coil and 400 turns in the secondary coil. If the input voltage is 120 V, what is the output voltage (assuming an ideal transformer)?

Accepted Answer

$$V_s = 480 V$$

Question 10

Which of the following best explains why a changing magnetic field induces an electric field?

Accepted Answer

Faraday's Law: $$\mathcal{E} = -\dfrac{d\Phi_B}{dt}$$

Question 11

A thin film of oil ($$n = 1.4) $$floats on water ($$n = 1.33). $$For constructive interference in reflected light at normal incidence, what is the minimum nonzero thickness $$d of $$the oil film for wavelength $$\lambda in $$air?

Accepted Answer

$$d = \dfrac{\lambda}{4n}$$

Question 12

Which of the following correctly ranks electromagnetic waves from largest to smallest wavelength?

Accepted Answer

radio $$\u003e$$ optical/visible $$\u003e X-$$ray $$\u003e$$ gamma ray

Question 13

A permanent bar magnet is cut into two pieces along its length. What happens to the magnetic poles of the resulting pieces?

Accepted Answer

Each piece becomes a smaller magnet with both a north and a south pole

Question 14

A velocity selector for an electron beam is set up with perpendicular electric and magnetic fields. If the electric field is $$E$$ and the magnetic field is $$B$$, what speed $$v$$ will allow electrons to pass through undeflected?

Accepted Answer

$$v = \dfrac{E}{B}$$

Question 15

A circular loop of radius $$R is in a $$region of uniform magnetic field $$B$$ directed to the right. If the direction of the magnetic field is reversed, what should be the orientation of the loop's area vector to minimize the magnetic flux through the loop?

Accepted Answer

180$$^\circ$$ with respect to the original orientation

Question 16

An AC source produces voltage $$V(t) = V_0$ \sin(\omega t)$$ and is connected to an inductor in series. When the current in the inductor is at its maximum value, what is the voltage across the inductor?

Accepted Answer

0

Question 17

Which of Maxwell's equations states that the net magnetic flux through any closed surface is zero?

Accepted Answer

$$\oint \vec{B} \cdot d\vec{A} = 0$$

Question 18

A long, straight wire carries a current $$I. $$What is the magnitude of the magnetic field at a distance $$r$$ from the wire?

Accepted Answer

$$B = \dfrac{\mu_0$ I}{2\pi r}$$

Question 19

The energy stored in a capacitor with capacitance $$C$$ and voltage $$V is $$given by:

Accepted Answer

$$U = \dfrac{1}{2} C V^2$

Electromagnetism and AC Circuits: Key Concepts and Practice Questions

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