Q: For the circuit in the third image, both resistors have resistance $$1\ \Omega$$, the battery has EMF $$1\ \text{V}$$, and the capacitor has capacitance $$1.0\ \text{nC}. $$Initially, the capacitor is uncharged. What is the current through $$R_1 (a) $$the instant the switch is closed and (b) a very long time after the switch is closed?

(a) $$1\ \text{A}$$ and (b) $$0$$

Question 1

A circuit consists of three resistors arranged as shown in the first image, with $$R_1 = 15$$\ \Omega$$, R_2$ = 25\ \Omega$$, $$R_3 = 5.0$$\ \Omega$$, and an EMF $$\mathcal{E} = 95\ 	ext{V}$$. If the current through each R_1$ is equal and the current through each R_2$ is equal, which equation correctly represents the sum of potential differences around the loop $$ACBA$$ using Kirchhoff’s rules?

Accepted Answer

$$\mathcal{E} - I$$_{R_2}$$R_2$$ - $$I_{R_3}R_3$ - I$$_{R_1}$$R_1 = 0$

Question 2

In the circuit shown in the second image, what is the voltage across the $$100\ \mu	ext{F}$$ capacitor after the circuit has been running for a very long time?

Accepted Answer

$$65\ 	ext{V}$$

Question 3

For the circuit in the third image, both resistors have resistance $$1\ \Omega$$, the battery has EMF $$1\ 	ext{V}$$, and the capacitor has capacitance $$1.0\ 	ext{nC}. $$Initially, the capacitor is uncharged. What is the current through $$R_1 (a) $$the instant the switch is closed and (b) a very long time after the switch is closed?

Accepted Answer

(a) $$1\ 	ext{A}$$ and (b) $$0$$

Question 4

A wire of length $$L$$ carrying current $$I is $$bent into a square loop and placed in a uniform magnetic field $$B. If $$the dipole is in its lowest energy state, what is the value of its energy?

Accepted Answer

$$-IL^2B$

Question 5

A positive point charge $$q$$ moves with velocity $$\vec{v}$$ next to a long, straight wire carrying current $$I$$ downward, as shown in the fourth image. If the force on the charge is downward, parallel to the current, which direction could $$\vec{v} be$$?

Accepted Answer

To the left

Question 6

What is the value of $$\int_C \vec{B} \cdot d\vec{l}$$ for the Ampèrian path $$C$$ drawn around three wires, two carrying current into the page and one out, as shown in the study materials?

Accepted Answer

$$0$$

Question 7

A proton with mass $$1.67 	imes 10$$^{-27}$$\ 	ext{kg}$$ and charge $$+e$$ enters a region with a uniform magnetic field $$B = 0.15\ 	ext{T}$$ pointing in the $$+z$$ direction. If its velocity has a component perpendicular to $$B$$, what is the radius of its circular path?

Accepted Answer

$$r = \frac{mv}{eB}$$

Question 8

Which equation correctly expresses the relationship between electric field and electric potential?

Accepted Answer

$$\vec{E} = -\vec{
abla}V$$

Question 9

A parallel plate capacitor is filled with a dielectric of dielectric constant $$\kappa. $$What is the new capacitance?

Accepted Answer

$$C = \kappa C_0$

Question 10

A resistor of resistance $$R is $$connected to a battery of voltage $$V. $$What is the power dissipated in the resistor?

Accepted Answer

$$P = \frac{V^2$}{R}$$

Question 11

A capacitor is charged to voltage $$V$$ and then disconnected from the battery. If the plates are pulled apart to double the separation, what happens to the energy stored in the capacitor?

Accepted Answer

It increases by a factor of four

Question 12

Which formula gives the energy density of the electric field in vacuum?

Accepted Answer

$$u_e = \frac{1}{2}\$$epsilon_0$$ E^2$

Question 13

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

Accepted Answer

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

Question 14

Which equation describes the charging of a capacitor through a resistor?

Accepted Answer

$$Q = Q_f(1 - e$$^{-t/RC}$$)$$

Question 15

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

Accepted Answer

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

Question 16

A metal wire has resistivity $$\$$rho_0$$ at temperature T_0$. If the temperature increases to T$, what is the new resistivity?

Accepted Answer

$$\rho = \$$rho_0$$ + \$$rho_0$$ \alpha (T - T_0$)$$

Question 17

Which formula gives the capacitance of a parallel plate capacitor?

Accepted Answer

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

Question 18

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

Accepted Answer

$$F = ILB$$

Question 19

A capacitor is connected in series with a resistor and a battery. What is the time constant $$	au$$ for the circuit?

Accepted Answer

$$	au = RC$$

Physics 1302W Practice Quiz #3 Study Guidance

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