Q: A $$5\,\mu\text{C}$$ point charge is placed at the origin. What is the electric field at a point $$0.2\,\text{m}$$ away from the charge?

$$E = \frac{1}{4\pi\$$varepsilon_0$$} \frac{5 \times 10$$^{-6}$$}{(0.2)^2$}$$

Question 1

Which of the following statements best describes Gauss's Law?

Accepted Answer

The net electric flux through any closed surface is equal to the total charge enclosed divided by the permittivity of free space: $$\Phi_E = \frac{Q_{	ext{enc}}}{\$$varepsilon_0$$}$$

Question 2

A parallel-plate capacitor is charged and then disconnected from the battery. If the plates are pulled apart to double their original separation, what happens to the potential difference across the plates?

Accepted Answer

It doubles.

Question 3

Which of the following correctly expresses the relationship between electric potential $$V$$ and electric field $$E in a $$uniform field?

Accepted Answer

$$E = -\frac{\Delta V}{d}$$

Question 4

A $$2\,\mu	ext{F}$$ capacitor and a $$4\,\mu	ext{F}$$ capacitor are connected in series across a $$12\,	ext{V}$$ battery. What is the total energy stored in the capacitors?

Accepted Answer

$$32\,\mu	ext{J}$$

Question 5

A point charge $$+Q is $$placed at the center of a spherical conducting shell that is initially uncharged. What is the net charge on the inner surface of the shell?

Accepted Answer

$$-Q$$

Question 6

Which of the following is true about the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

The electric field is zero everywhere inside the conductor.

Question 7

A $$10\,\Omega$$ resistor and a $$20\,\Omega$$ resistor are connected in parallel. What is the equivalent resistance?

Accepted Answer

$$6.67\,\Omega$$

Question 8

A battery of emf $$12\,	ext{V}$$ and internal resistance $$1\,\Omega is $$connected to a $$5\,\Omega$$ resistor. What is the current in the circuit?

Accepted Answer

$$2\,	ext{A}$$

Question 9

Which of the following best describes the direction of the electric field created by a positive point charge?

Accepted Answer

Radially outward from the charge

Question 10

A wire carries a current of $$3\,	ext{A}$$ for $$4\,	ext{s}. $$How much charge passes through the wire in this time?

Accepted Answer

$$12\,	ext{C}$$

Question 11

A $$6\,\mu	ext{F}$$ and a $$3\,\mu	ext{F}$$ capacitor are connected in parallel. What is their equivalent capacitance?

Accepted Answer

$$9\,\mu	ext{F}$$

Question 12

A $$12\,	ext{V}$$ battery is connected to a circuit with two resistors, $$R_1 = 4$$\,\Omega$$ and R_2$ = 8\,\Omega$$, in series. What is the voltage drop across $$R_2$$?

Accepted Answer

$$8\,	ext{V}$$

Question 13

Which of the following is the correct expression for the electric potential energy $$U of $$two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

$$U = \frac{1}{4\pi\$$varepsilon_0$$} \frac{q_1$ q_2$}{r}$$

Question 14

A student uses Gauss's law to find the electric field inside a uniformly charged solid sphere of radius $$R$$ and total charge $$Q. $$What is the electric field at a distance $$r \u003c R$$ from the center?

Accepted Answer

$$E = \frac{1}{4\pi\$$varepsilon_0$$} \frac{Q r}{R^3$}$$

Question 15

A $$9\,	ext{V}$$ battery is connected to a resistor. If $$27\,	ext{C} of $$charge flows through the resistor in $$3\,	ext{s}$$, what is the resistance?

Accepted Answer

$$1\,\Omega$$

Question 16

Which of the following is a correct application of Kirchhoff's loop law?

Accepted Answer

The sum of the potential differences around any closed loop is zero: $$\sum \Delta V = 0$$

Question 17

A $$5\,\mu	ext{C}$$ point charge is placed at the origin. What is the electric field at a point $$0.2\,	ext{m}$$ away from the charge?

Accepted Answer

$$E = \frac{1}{4\pi\$$varepsilon_0$$} \frac{5 	imes 10$$^{-6}$$}{(0.2)^2$}$$

Question 18

A real-world application: In a defibrillator, a $$100\,\mu	ext{F}$$ capacitor is charged to $$2000\,	ext{V}$$ and then discharged through a patient's chest. How much energy is delivered?

Accepted Answer

$$400\,	ext{J}$$

Question 19

Which of the following statements about capacitors in series is correct?

Accepted Answer

The reciprocal of the equivalent capacitance is the sum of the reciprocals of the individual capacitances: $$\frac{1}{C_{	ext{eq}}} = \frac{1}{C_1$} + \frac{1}{C_2$} + \cdots$$

Question 20

A $$12\,	ext{V}$$ battery is connected to a circuit with a $$6\,\Omega$$ resistor and a $$3\,\Omega$$ resistor in parallel. What is the total current supplied by the battery?

Accepted Answer

$$6\,	ext{A}$$

PHY1020U Midterm Study Guide: Electric Charges, Fields, Potential, and Circuits

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