Q: The power dissipated in a resistor is given by $$P = IV. $$For a $$10\ \Omega$$ resistor with $$2\ \mathrm{A} of $$current, what is the power dissipated?

$$P = I^2$R = (2)^2$ \times 10 = 40\ \mathrm{W}$$

Question 1

Which of the following best describes the SI unit of electric current?

Accepted Answer

Coulomb per second ($$1\ \mathrm{C/s}$$), also known as the ampere ($$1\ \mathrm{A})$$

Question 2

A battery is rated at $$12\ \mathrm{V}$$ emf. What does this value represent?

Accepted Answer

The electric potential difference between the battery terminals when no current is drawn

Question 3

Which statement about the direction of electric current is correct?

Accepted Answer

It is defined as the direction a positive charge would move in the circuit

Question 4

Ohm’s law is given by $$V = IR. $$Which of the following materials does Ohm’s law apply to?

Accepted Answer

Most metallic conductors

Question 5

A copper wire and an aluminum wire have the same length and diameter. Which property determines which wire has greater resistance?

Accepted Answer

Resistivity of the material

Question 6

Which of the following statements about superconductors is correct?

Accepted Answer

Their resistivity drops to zero below a critical temperature $$T_C$$

Question 7

The power dissipated in a resistor is given by $$P = IV. $$For a $$10\ \Omega$$ resistor with $$2\ \mathrm{A} of $$current, what is the power dissipated?

Accepted Answer

$$P = I^2$R = (2)^2$ 	imes 10 = 40\ \mathrm{W}$$

Question 8

Three resistors, $$R_1 = 2$$\ \Omega$$, R_2$ = 3\ \Omega$$, and $$R_3 = 5$$\ \Omega$$, are connected in series. What is the equivalent resistance?

Accepted Answer

$$R_{eq} = R_1$ + R_2$ + R_3$ = 10\ \Omega$$

Question 9

Two resistors, $$R_1 = 4$$\ \Omega$$ and R_2$ = 12\ \Omega$$, are connected in parallel. What is the equivalent resistance?

Accepted Answer

$$R_{eq} = 1/(1/4 + 1/12) = 3\ \Omega$$

Question 10

Which of the following is a correct application of Kirchhoff’s junction rule?

Accepted Answer

The total current entering a junction equals the total current leaving the junction

Question 11

A circuit contains a $$12\ \mathrm{V}$$ battery and three resistors in series: $$2\ \Omega$$, $$3\ \Omega$$, and $$5\ \Omega. $$What is the current in the circuit?

Accepted Answer

$$I = V/R_{eq} = 12 / (2 + 3 + 5) = 12 / 10 = 1.2\ \mathrm{A}$$

Question 12

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

Accepted Answer

The equivalent capacitance is the sum of the individual capacitances: $$C_{eq} = C_1$ + C_2$ + ...$$

Question 13

A $$10\ \mu\mathrm{F}$$ and a $$20\ \mu\mathrm{F}$$ capacitor are connected in series. What is the equivalent capacitance?

Accepted Answer

$$1/C_{eq} = 1/10 + 1/20 = 3/20 \Rightarrow C_{eq} = 20/3 = 6.67\ \mu\mathrm{F}$$

Question 14

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

Accepted Answer

$$	au = RC$$

Question 15

Which device should have as low a resistance as possible to minimize its effect on the circuit?

Accepted Answer

Ammeter

Question 16

A household uses $$500\ \mathrm{kWh} of $$energy in a month. If the cost is $$0.12$$ per $$\mathrm{kWh}$$, what is the total cost?

Accepted Answer

$$500 	imes 0.12 = \60$

Question 17

Which of the following best describes the behavior of a voltmeter in a circuit?

Accepted Answer

It is connected in parallel and should have a very large resistance

Question 18

A $$9\ \mathrm{V}$$ battery is connected to a $$3\ \Omega$$ resistor. How much energy is dissipated as heat in $$2$$ minutes?

Accepted Answer

$$E = P t = (V^2$/R) t = (9^2$/3) 	imes 120 = (81/3) 	imes 120 = 27 	imes 120 = 3240\ \mathrm{J}$$

Electric Current and Direct-Current Circuits: Study Notes

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