Q: Which trigonometric identity is used to find the angle $$\theta in a $$right triangle given opposite and adjacent sides?

$$\tan \theta = \frac{\text{opp}}{\text{adj}}$$

Question 1

Three positive charges of $$+17.0\ \mu\mathrm{C}$$ are placed at the corners of an equilateral triangle with sides of $$15.0\ \mathrm{cm}. $$What is the magnitude of the net force on one charge due to the other two? (Use $$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$)

Accepted Answer

$$F = 166\ \mathrm{N}$$

Question 2

For the triangle of charges in the previous question, what is the direction of the net force on the top charge?

Accepted Answer

Directly downward

Question 3

A 100 W lightbulb has a resistance of $$12.0\ \Omega$$ when cold ($$20^\circC) $$and $$140.0\ \Omega$$ when hot. If the temperature coefficient of resistivity is $$\alpha = 0.0045\ ({}^\circ\mathrm{C}$$)^{-1}$$, what is the estimated temperature of the filament when hot?

Accepted Answer

$$T = 2600^\circ\mathrm{C}$$

Question 4

Which equation correctly relates the resistance of a material to its temperature?

Accepted Answer

$$R = R_0$ [1 + \alpha (T - T_0$)]$$

Question 5

A negative charge moves to the right ($$+x$$ direction) in a magnetic field pointing out of the page. What is the direction of the magnetic force on the charge?

Accepted Answer

Downward ($$-y$$ direction)

Question 6

Which formula gives the magnitude of the force on a charge $$q$$ moving with velocity $$v$$ perpendicular to a magnetic field $$B$$?

Accepted Answer

$$F = qvB$$

Question 7

If two resistors, $$R_1 = 10$$\ \Omega$$ and R_2$ = 20\ \Omega$$, are connected in parallel, what is the equivalent resistance?

Accepted Answer

$$R_{eq} = 6.67\ \Omega$$

Question 8

A charge of $$2.0\ \mu\mathrm{C} is $$placed in an electric field of $$5.0 	imes 10^4$\ \mathrm{N/C}. $$What is the force on the charge?

Accepted Answer

$$F = 0.10\ \mathrm{N}$$

Question 9

Which of the following best describes the direction of the force on a negative charge moving perpendicular to a magnetic field?

Accepted Answer

It is perpendicular to both the velocity and the magnetic field, but opposite to the right-hand rule.

Question 10

A wire carries a current $$I in a $$magnetic field $$B$$ perpendicular to the wire. What is the magnitude of the force on a length $$L of $$the wire?

Accepted Answer

$$F = BIL$$

Question 11

A capacitor with capacitance $$C is $$charged to a voltage $$V. $$What is the energy stored in the capacitor?

Accepted Answer

$$U = \frac{1}{2}CV^2$

Question 12

Which equation gives the equivalent capacitance for two capacitors $$C_1$$ and $$C_2 in $$series?

Accepted Answer

$$\frac{1}{C_{eq}} = \frac{1}{C_1$} + \frac{1}{C_2$}$$

Question 13

A solenoid has $$N$$ turns, length $$l$$, and carries current $$I. $$What is the magnetic field inside the solenoid?

Accepted Answer

$$B = \mu_0$ \frac{N}{l} I$$

Question 14

A $$5.0\ \mu\mathrm{F}$$ capacitor is charged to $$12\ \mathrm{V}. $$How much charge is stored on the capacitor?

Accepted Answer

$$Q = 60\ \mu\mathrm{C}$$

Question 15

Which trigonometric identity is used to find the angle $$	heta in a $$right triangle given opposite and adjacent sides?

Accepted Answer

$$	an 	heta = \frac{	ext{opp}}{	ext{adj}}$$

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