Q: A toaster rated at 1200 W is plugged into a 120 V outlet. What is the current drawn by the toaster?

$I = \frac{P}{V} = \frac{1200}{120} = 10\ \text{A}$

Q: Two resistors, $R_1 = 10\ \Omega$ and $R_2 = 20\ \Omega$, are connected in series with a 6 V source. What is the current through the resistors?

$I = \frac{V}{R_1 + R_2} = \frac{6}{30} = 0.2\ \text{A}$

Q: Two resistors, $R_1 = 10\ \Omega$ and $R_2 = 20\ \Omega$, are connected in parallel. What is their equivalent resistance?

$R_{eq} = \frac{R_1 R_2}{R_1 + R_2} = \frac{10 \times 20}{10 + 20} = \frac{200}{30} \approx 6.67\ \Omega$

Q: Which material from the table has the lowest resistivity and is therefore the best electrical conductor?

Silver, $\rho = 1.59 \times 10^{-8}\ \Omega \cdot m$

Question 1

Which of the following best describes electric current in a conductor?

Accepted Answer

The amount of charge per unit time passing through a surface perpendicular to the motion of charges.

Question 2

A battery produces a difference in electric potential between its terminals. What is the term for the maximum potential difference across the terminals?

Accepted Answer

Electromotive force (emf), $\varepsilon$

Question 3

According to Ohm’s Law, what is the relationship between voltage ($V$), current ($I$), and resistance ($R$)?

Accepted Answer

$V = IR$

Question 4

A copper wire has length $L$ and cross-sectional area $A$. Its resistance $R$ is given by:

Accepted Answer

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

Question 5

Which statement about resistivity and temperature is correct?

Accepted Answer

For conductors, resistivity increases with increasing temperature.

Question 6

A toaster rated at 1200 W is plugged into a 120 V outlet. What is the current drawn by the toaster?

Accepted Answer

$I = \frac{P}{V} = \frac{1200}{120} = 10\ 	ext{A}$

Question 7

Two resistors, $R_1 = 10\ \Omega$ and $R_2 = 20\ \Omega$, are connected in series with a 6 V source. What is the current through the resistors?

Accepted Answer

$I = \frac{V}{R_1 + R_2} = \frac{6}{30} = 0.2\ 	ext{A}$

Question 8

Three resistors, $R_1 = 11\ \Omega$, $R_2 = 53\ \Omega$, and $R_3$, are connected in series with a 24 V battery. The total current is 0.16 A. What is the value of $R_3$?

Accepted Answer

$R_3 = \frac{V}{I} - (R_1 + R_2) = \frac{24}{0.16} - (11 + 53) = 150 - 64 = 86\ \Omega$

Question 9

Which of the following is true for resistors connected in parallel?

Accepted Answer

The same voltage is applied across each resistor.

Question 10

Two resistors, $R_1 = 10\ \Omega$ and $R_2 = 20\ \Omega$, are connected in parallel. What is their equivalent resistance?

Accepted Answer

$R_{eq} = \frac{R_1 R_2}{R_1 + R_2} = \frac{10 	imes 20}{10 + 20} = \frac{200}{30} \approx 6.67\ \Omega$

Question 11

Which material from the table has the lowest resistivity and is therefore the best electrical conductor?

Accepted Answer

Silver, $ho = 1.59 	imes 10^{-8}\ \Omega \cdot m$

Question 12

Capacitors connected in parallel have which of the following properties?

Accepted Answer

The total capacitance is the sum of the individual capacitances: $C_{eq} = C_1 + C_2 + \ldots$

Question 13

In an RC circuit, the time constant $	au$ is given by:

Accepted Answer

$	au = RC$

Question 14

A resistor $R = 100\ \Omega$ and a capacitor $C = 200\ \mu	ext{F}$ are connected in series. How long does it take to charge the capacitor to 99% of its maximum charge?

Accepted Answer

$t = -RC \ln(1 - 0.99) = -100 	imes 200 	imes 10^{-6} \ln(0.01) \approx 0.92\ 	ext{s}$

Question 15

In a heart pacemaker, a pulse is delivered every time a fully charged capacitor loses 67% of its original charge through a resistance of $1.7 	imes 10^6\ \Omega$. If 81 pulses are delivered per minute, what is the capacitance of the capacitor?

Accepted Answer

$C = \frac{t}{R \ln(1/0.33)} = \frac{60/81}{1.7 	imes 10^6 \ln(1/0.33)} \approx 1.2 \mu	ext{F}$

Question 16

Which of the following best describes the charging of a capacitor in an RC circuit?

Accepted Answer

The charge on the capacitor increases exponentially and approaches a maximum value $q = CE$ as $t 	o \infty$.

Question 17

Which real-world application uses RC circuits to control timing of voltage pulses?

Accepted Answer

Heart pacemakers

Question 18

If a circuit contains both resistors and capacitors, which statement is true about the charging and discharging of the capacitor?

Accepted Answer

Charging and discharging do not occur instantaneously; they follow exponential time dependence.

CH 21: Electric Current and DC Circuits

Study Guide - Practice Questions

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