Q: A pocket calculator uses a 3.0 V battery and draws a current of 0.17 mA for one hour. How much charge flows through the circuit?

$$q = 0.17 \times 10$$^{-3}$$ \times 3600 = 0.612$$ \text{C}

Q: Two resistors, 6.00 $$\Omega$$ and 3.00 $$\Omega$$, are connected in series to a 12.0 V battery. What is the current in the circuit?

$$I = \frac{12.0}{9.00} = 1.33\ \text{A}$$

Q: Two resistors, 8.00 $$\Omega$$ and 4.00 $$\Omega$$, are connected in parallel. What is their equivalent resistance?

$$R_P = \frac{8.00 \times 4.00}{8.00 + 4.00} = 2.67\ \Omega$$

Q: A flashlight bulb operates at 3.0 V and draws 0.40 A. What is the power delivered to the bulb?

$$P = 3.0 \times 0.40 = 1.2\ \text{W}$$

Q: A car battery has an emf of 12.0 V and an internal resistance of 0.0100 $$\Omega. $$What is the terminal voltage when the current drawn is 100.0 A?

$$V = 12.0 - (100.0 \times 0.0100) = 11.0\ \text{V}$$

Question 1

Which equation correctly defines electric current in terms of charge and time?

Accepted Answer

$$I = \frac{\Delta q}{\Delta t}$$

Question 2

A pocket calculator uses a 3.0 V battery and draws a current of 0.17 mA for one hour. How much charge flows through the circuit?

Accepted Answer

$$q = 0.17 	imes 10$$^{-3}$$ 	imes 3600 = 0.612$$ 	ext{C}

Question 3

Which statement best describes conventional current?

Accepted Answer

It is the hypothetical flow of positive charges that would have the same effect as the actual movement of negative charges.

Question 4

What is the maximum potential difference across the terminals of a battery called?

Accepted Answer

Electromotive force (emf)

Question 5

According to Ohm’s Law, what is the relationship between voltage, current, and resistance?

Accepted Answer

$$V = IR$$

Question 6

A torch uses two 1.5 V batteries to provide a current of 0.40 A in the filament. What is the resistance of the glowing filament?

Accepted Answer

$$R = \frac{3.0}{0.40} = 7.5\ \Omega$$

Question 7

The resistance of a wire is given by $$R = \rho \frac{L}{A}. If $$the length of the wire is doubled and the cross-sectional area is halved, what happens to the resistance?

Accepted Answer

It is quadrupled.

Question 8

Two resistors, 6.00 $$\Omega$$ and 3.00 $$\Omega$$, are connected in series to a 12.0 V battery. What is the current in the circuit?

Accepted Answer

$$I = \frac{12.0}{9.00} = 1.33\ 	ext{A}$$

Question 9

Two resistors, 8.00 $$\Omega$$ and 4.00 $$\Omega$$, are connected in parallel. What is their equivalent resistance?

Accepted Answer

$$R_P = \frac{8.00 	imes 4.00}{8.00 + 4.00} = 2.67\ \Omega$$

Question 10

A flashlight bulb operates at 3.0 V and draws 0.40 A. What is the power delivered to the bulb?

Accepted Answer

$$P = 3.0 	imes 0.40 = 1.2\ 	ext{W}$$

Question 11

A car battery has an emf of 12.0 V and an internal resistance of 0.0100 $$\Omega. $$What is the terminal voltage when the current drawn is 100.0 A?

Accepted Answer

$$V = 12.0 - (100.0 	imes 0.0100) = 11.0\ 	ext{V}$$

Question 12

How should an ammeter be connected in a circuit to measure current?

Accepted Answer

In series with the circuit element.

Question 13

Why is alternating current (AC) preferred for power transmission over long distances?

Accepted Answer

AC can be easily transformed to higher or lower voltages with minimal power loss.

Question 14

What is the function of marker balls ('balloons') on high-voltage transmission lines?

Accepted Answer

To keep low-flying airplanes from flying into them.

Question 15

Why do birds not get electrocuted when perching on a single power line?

Accepted Answer

Because there is no potential difference across their bodies.

Question 16

Which device is used to protect against over-current in electrical circuits?

Accepted Answer

A fuse

Question 17

If a wire has a resistivity $$\rho$$, length $$L$$, and cross-sectional area $$A$$, what is the resistance?

Accepted Answer

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

Question 18

Which formula gives the electric power delivered to a circuit?

Accepted Answer

$$P = IV$$

Question 19

In a parallel circuit, what is true about the voltage across each device?

Accepted Answer

The voltage is the same across each device.

Direct Current Electricity: Fundamentals, Circuits, and Safety

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