Question 1

A proton and an electron are released from rest in a uniform electric field. Which particle accelerates more, and why?

Accepted Answer

The electron accelerates more, because it has a much smaller mass.

Question 2

Point charges $$+q$$, $$+q$$, and $$-2q$$ are at the corners of an isosceles triangle with equal side lengths $$a$$ and interior angle $$120^\circ$$, as shown. What is the direction of the total force on the $$-2q$$ charge?

Accepted Answer

Down

Question 3

Four point charges $$+q$$, $$+q$$, $$-q$$, and $$-q$$ are fixed at the corners of a square with side length $$a. $$What is the magnitude of the electric field at the center of the square, equidistant between the like charges?

Accepted Answer

$$\displaystyle \frac{2\sqrt{2}kq}{a^2$}$$

Question 4

A flat surface with area $$A is $$oriented within a uniform electric field $$\vec{E} so $$that the surface is perpendicular to the field lines. Which of the following will decrease the electric flux through the surface?

Accepted Answer

Rotate the surface so it is parallel to $$\vec{E}$$

Question 5

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

$$\displaystyle \frac{\kappa \$$varepsilon_0$$ A}{d}$$

Question 6

A capacitor is connected to a voltage source, charged, and then disconnected from the voltage source. If you then bring the plates of the capacitor closer together without touching each other, what happens to the electric potential energy stored in the capacitor?

Accepted Answer

It decreases.

Question 7

You have three $$3.0\,\mu\mathrm{F}$$ capacitors and want them to store a total of $$0.03\,\mathrm{J} of $$electric potential energy when connected to a $$20\,\mathrm{V}$$ EMF power source. How should you arrange the capacitors before connecting them to the EMF power source?

Accepted Answer

Two in parallel connected in series to one in series

Question 8

A constant current of $$1.0\,\mathrm{A}$$ flows in a wire. How many electrons pass a point in the wire in $$7.0$$ seconds? (Assume electrons are the charges carrying the current.)

Accepted Answer

$$4.4 	imes 10$$^{20}$$

Question 9

A resistor of $$5.0\,\Omega is $$connected in series with a $$10.0\,\Omega$$ resistor and a $$12\,\mathrm{V}$$ battery. What is the current running through the $$5.0\,\Omega$$ resistor?

Accepted Answer

$$0.80\,\mathrm{A}$$

Question 10

An $$RC$$ circuit contains a resistor $$R$$, a capacitor $$C$$, and an EMF source $$\mathcal{E} in $$series. If the capacitor is initially uncharged when the circuit is connected, how much time does it take for the capacitor to charge to $$0.62\mathcal{E}$$?

Accepted Answer

$$RC$$

Question 11

A $$RC$$ circuit contains a resistor with resistance $$R$$, a capacitor with capacitance $$C$$, and an EMF source $$\mathcal{E} in $$series. If the capacitor is initially uncharged when the circuit is connected, it takes $$RC$$ seconds for the capacitor to charge to half its maximum charge. After charging, this capacitor is disconnected from the EMF source, and the resistor and capacitor are placed in parallel with an uncharged capacitor of the same capacitance. You close the loop so the original capacitor can discharge into the new one. When you re-open the circuit, how long will it take for the new capacitor to charge to half its maximum charge?

Accepted Answer

$$0.69RC$$

Question 12

Which of the following best describes the direction of the electric field at a point near a positive point charge?

Accepted Answer

Radially outward from the charge

Question 13

A $$10\,\mu\mathrm{C}$$ point charge is placed at the center of a spherical conducting shell of inner radius $$0.10\,\mathrm{m}$$ and outer radius $$0.15\,\mathrm{m}. $$The shell is grounded. What is the electric field just outside the shell?

Accepted Answer

$$0$$

Question 14

Which of the following statements about the energy stored in a capacitor is correct?

Accepted Answer

The energy stored is $$U = \frac{1}{2}CV^2$.

Question 15

A wire of length $$L$$ and cross-sectional area $$A$$ has a resistance $$R. If $$the length is doubled and the area is halved, what is the new resistance?

Accepted Answer

$$8R$$

Question 16

Which of the following best describes the effect of inserting a dielectric material between the plates of a capacitor while it is connected to a battery?

Accepted Answer

The capacitance increases and the charge on the plates increases.

Question 17

A $$12\,\mathrm{V}$$ battery is connected to a $$6.0\,\Omega$$ resistor and a $$3.0\,\Omega$$ resistor in series. What is the current in the circuit?

Accepted Answer

$$1.3\,\mathrm{A}$$

Question 18

Which of the following is the correct expression for the electric potential at a distance $$r$$ from a point charge $$q$$?

Accepted Answer

$$\displaystyle V = \frac{1}{4\pi\$$varepsilon_0$$} \frac{q}{r}$$

Question 19

A $$5.0\,\mu\mathrm{F}$$ capacitor is charged to $$10\,\mathrm{V}$$ and then disconnected from the battery. If the plates are pulled apart so the distance between them doubles, what happens to the voltage across the plates?

Accepted Answer

It doubles.

Electrostatics and Circuits: Physics Study Guide and Practice Questions

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