Q: A wire 25 cm long is placed perpendicular to a 1000 T magnetic field and experiences a force of 160 N. What current flows through the wire?

$$I = \frac{F}{B L} = \frac{160}{1000 \times 0.25} = 0.64\ \mathrm{A}$$

Q: A +20 pC charge with a mass of 2 μg moves perpendicular to a 0.080 T magnetic field at 4.8 cm/s. What is its acceleration?

$$a = \frac{q v B}{m} = \frac{20 \times 10$$^{-12}$$ \times 0.048 \times 0.080}{2 \times 10$$^{-9}$$} = 3.85 \times 10$$^{-5}$$\ \mathrm{m/s^2$}$$

Q: A beam of light in air strikes mineral oil at $$23.1^\circ$$ with the normal. If the speed of light in oil is $$2.17 \times 10^8$\ \mathrm{m/s}$$, what is the angle of refraction?

$$n_{\text{oil}} = \frac{c}{v} = \frac{3.00 \times 10^8$}{2.17 \times 10^8$} = 1.38$$; $$n_{\text{air}} \sin \$$theta_1$$ = n_{\text{oil}} \sin \$$theta_2$$; $$\sin \$$theta_2$$ = \frac{1.00 \times \sin 23.1^\circ}{1.38} = 0.283$$; $$\$$theta_2 = 16.5$$^\circ$$

Q: A plastic pipe (n = 1.53) is submerged in water (n = 1.33). What is the minimum angle of incidence for total internal reflection at the pipe-water interface?

$$\sin \theta_c = \frac{n_{\text{water}}}{n_{\text{pipe}}} = \frac{1.33}{1.53} = 0.87$$; $$\theta_c = \arcsin(0.87) = 60.4^\circ$$

Question 1

A proton moves at a velocity perpendicular to a uniform magnetic field. Which of the following correctly describes the direction of the magnetic force acting on the proton?

Accepted Answer

The force is perpendicular to both the velocity and the magnetic field, as determined by the right-hand rule.

Question 2

Why are there no magnetic monopoles observed in nature, unlike electric charges?

Accepted Answer

Because magnetic field lines always form closed loops, so isolated north or south poles cannot exist.

Question 3

A wire 25 cm long is placed perpendicular to a 1000 T magnetic field and experiences a force of 160 N. What current flows through the wire?

Accepted Answer

$$I = \frac{F}{B L} = \frac{160}{1000 	imes 0.25} = 0.64\ \mathrm{A}$$

Question 4

Which of the following best describes the effect of increasing the number of turns in a solenoid, all else being equal?

Accepted Answer

The magnetic field inside the solenoid increases.

Question 5

A +20 pC charge with a mass of 2 μg moves perpendicular to a 0.080 T magnetic field at 4.8 cm/s. What is its acceleration?

Accepted Answer

$$a = \frac{q v B}{m} = \frac{20 	imes 10$$^{-12}$$ 	imes 0.048 	imes 0.080}{2 	imes 10$$^{-9}$$} = 3.85 	imes 10$$^{-5}$$\ \mathrm{m/s^2$}$$

Question 6

A beam of light in air strikes mineral oil at $$23.1^\circ$$ with the normal. If the speed of light in oil is $$2.17 	imes 10^8$\ \mathrm{m/s}$$, what is the angle of refraction?

Accepted Answer

$$n_{	ext{oil}} = \frac{c}{v} = \frac{3.00 	imes 10^8$}{2.17 	imes 10^8$} = 1.38$$; $$n_{	ext{air}} \sin \$$theta_1$$ = n_{	ext{oil}} \sin \$$theta_2$$; $$\sin \$$theta_2$$ = \frac{1.00 	imes \sin 23.1^\circ}{1.38} = 0.283$$; $$\$$theta_2 = 16.5$$^\circ$$

Question 7

Which of the following statements about total internal reflection is correct?

Accepted Answer

It occurs when light travels from a medium with higher index of refraction to one with lower index, and the angle of incidence exceeds the critical angle.

Question 8

A plastic pipe (n = 1.53) is submerged in water (n = 1.33). What is the minimum angle of incidence for total internal reflection at the pipe-water interface?

Accepted Answer

$$\sin 	heta_c = \frac{n_{	ext{water}}}{n_{	ext{pipe}}} = \frac{1.33}{1.53} = 0.87$$; $$	heta_c = \arcsin(0.87) = 60.4^\circ$$

Question 9

Which of the following best describes the difference between a real image and a virtual image?

Accepted Answer

A real image can be projected onto a screen, while a virtual image cannot.

Question 10

A convex lens of focal length 15.0 cm is used as a magnifying glass. At what distance from a postage stamp should you hold the lens to get a magnification of +2.00?

Accepted Answer

$$M = \frac{s_i}{s_o}$$; $$\frac{1}{f} = \frac{1}{s_o} + \frac{1}{s_i}$$; $$M = \frac{f}{s_o - f} = 2.00$$; $$s_o = 7.5\ \mathrm{cm}$$

Question 11

Which of the following statements about the law of reflection is correct?

Accepted Answer

The angle of incidence equals the angle of reflection, both measured from the normal.

Question 12

A unicycle wheel has 200 turns of wire around its rim (diameter 2.5 cm). The magnetic field perpendicular to the wheel decreases from 0.68 T to 0.24 T in 4.5 s. What is the induced emf?

Accepted Answer

$$\epsilon = -N \frac{\Delta \Phi}{\Delta t}$$; $$A = \pi r^2$ = \pi (0.0125)^2$; $$\Delta B = 0.24 - 0.68 = -0.44$$; $$\epsilon = 200 	imes \frac{\pi $$(0.0125)^2$$ 	imes 0.44}{4.5} = 9.6\ \mathrm{mV}$$

Question 13

Which of the following best describes what happens to the magnetic field around a current-carrying wire as you increase the distance from the wire?

Accepted Answer

The magnetic field decreases in magnitude.

Question 14

Two parallel wires carry equal currents in opposite directions. What is the nature of the force between them?

Accepted Answer

The wires repel each other.

Question 15

Which of the following best describes the effect of increasing the number of slits in a diffraction grating?

Accepted Answer

The maxima become sharper and more widely spaced.

Question 16

A spherical Christmas ornament is 6.00 cm in diameter. What is the magnification of an object placed 10.0 cm away from the ornament, and is the image upright or inverted?

Accepted Answer

$$f = \frac{R}{2} = 3.00\ \mathrm{cm}$$; $$\frac{1}{f} = \frac{1}{s_o} + \frac{1}{s_i}$$; $$M = \left| \frac{s_i}{s_o} \right| = 0.13$$; image is upright.

Question 17

Which of the following best describes the difference between dispersion, interference, diffraction, and polarization?

Accepted Answer

Dispersion is the separation of light into colors; interference is the superposition of waves; diffraction is the bending of waves around obstacles; polarization is the orientation of wave oscillations.

Question 18

An LRC circuit has $$R = 25\ \Omega$$, $$L = 15\ \mathrm{mH}$$, $$C = 60\ \mu\mathrm{F}$$, and is connected to a $$120\ \mathrm{V}$$, $$250\ \mathrm{Hz} AC $$source. What is the power through the inductor?

Accepted Answer

$$P = I^2$ X_L = (2.68)^2$ 	imes (2\pi 	imes 250 	imes 0.015) = 428\ \mathrm{W}$$

Question 19

Which of the following statements about the index of refraction is correct?

Accepted Answer

It is the ratio of the speed of light in vacuum to the speed of light in the medium: $$n = \frac{c}{v}.$$

PHYS 0211 Final Exam Review: Step-by-Step Guidance for Magnetism, Induction, Optics, and Wave Optics Problems

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