Q: A capacitor of $$10\ \mu\text{F} is $$charged to $$12\ \text{V}$$ and then disconnected from the battery. What is the energy stored in the capacitor?

$$7.2 \times 10$$^{-4}$$\ \text{J}$$

Question 1

Immediately after the switch S is closed in the circuit shown (with $$R_1$$ = $$R_2$$ = $$R_3 = 1.0$$\ 	ext{M}\Omega$$, C = 10$$\ \mu	ext{F}$$, $$\mathcal{E} = 12\ 	ext{V}$$), what is the current through R_3$ at t = 0$?

Accepted Answer

$$0\ 	ext{A}$$

Question 2

A parallel-plate capacitor is filled with a dielectric of constant $$\kappa. If $$the original capacitance is $$C_0$$, what is the new capacitance?

Accepted Answer

$$C = \kappa C_0$

Question 3

In the velocity selector shown, what is the condition for a charged particle to pass through undeflected?

Accepted Answer

$$qE = $$qvB_1$$

Question 4

What is the equivalent resistance between points D and E in the circuit shown, where $$R_1$$ = $$R_2 = 4.00$$\ \Omega$$ and R_3$ = 2.50\ \Omega$$?

Accepted Answer

$$3.00\ \Omega$$

Question 5

Using Kirchhoff’s rules, what is the value and direction of the unknown current $$i in $$the circuit shown?

Accepted Answer

$$6\ 	ext{A}$$, upward

Question 6

A wire is bent into a circular loop of diameter $$d$$ and carries current $$I. $$Placed in a uniform magnetic field $$B$$ with its dipole moment aligned with the field, how much energy is required to rotate the loop by $$180^\circ$$?

Accepted Answer

$$2I\pi d^2$ B$$

Question 7

A positive point charge $$q$$ moves upward with velocity $$\vec{v}$$ next to a long, straight wire carrying current $$I$$ downward. What is the direction of the force on the charge?

Accepted Answer

To the right

Question 8

Which of the three wire configurations shown produces the largest magnitude magnetic field at the center of curvature (the dot)?

Accepted Answer

Configuration (a)

Question 9

A capacitor of $$10\ \mu	ext{F} is $$charged to $$12\ 	ext{V}$$ and then disconnected from the battery. What is the energy stored in the capacitor?

Accepted Answer

$$7.2 	imes 10$$^{-4}$$\ 	ext{J}$$

Question 10

A mass spectrometer separates boron-10 and boron-11 ions. If the radius of the boron-10 path is $$r_{10}$$, what is the radius of the boron-11 path?

Accepted Answer

$$r_{11} = \frac{11}{10} r_{10}$$

Question 11

The energy stored in a capacitor is given by which of the following expressions?

Accepted Answer

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

Question 12

A resistor of resistance $$R is $$connected to a battery of emf $$\mathcal{E}$$ and internal resistance $$r. $$What is the current in the circuit?

Accepted Answer

$$I = \frac{\mathcal{E}}{R + r}$$

Question 13

The electric field just outside the surface of a charged conductor in electrostatic equilibrium is:

Accepted Answer

$$E = \frac{\sigma}{\$$epsilon_0$$}$$

Question 14

A parallel-plate capacitor with plate area $$A$$ and separation $$d is $$filled with a dielectric of constant $$\kappa. $$What is the capacitance?

Accepted Answer

$$C = \frac{\kappa \$$epsilon_0$$ A}{d}$$

Question 15

A wire of length $$L$$ and cross-sectional area $$A$$ has resistivity $$\rho. $$What is its resistance?

Accepted Answer

$$R = \frac{\rho L}{A}$$

Question 16

A capacitor is being charged in an RC circuit. What is the time constant $$	au of $$the circuit?

Accepted Answer

$$	au = RC$$

Question 17

A point charge $$q is $$placed at the center of a spherical Gaussian surface of radius $$r. $$What is the electric flux through the surface?

Accepted Answer

$$\Phi_E = \frac{q}{\$$epsilon_0$$}$$

Physics 1302W Quiz #3 Study Guidance

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