Q: Which equation correctly expresses the average electric current $$I$$ passing through a surface of area $$A$$ when a charge $$ riangle Q$$ passes through in a time interval $$ riangle t$$?

$$I = \frac{\triangle Q}{\triangle t}$$

Q: A resistor’s value is marked by colored bands. If the first two bands are red and violet, and the third band is yellow, what is the resistance value?

$$27 \times 10^4$\ \Omega = 270,000\ \Omega$$

Question 1

Which equation correctly expresses the average electric current $$I$$ passing through a surface of area $$A$$ when a charge $$	riangle Q$$ passes through in a time interval $$	riangle t$$?

Accepted Answer

$$I = \frac{	riangle Q}{	riangle t}$$

Question 2

In a copper wire carrying a current, which statement best describes the motion of electrons?

Accepted Answer

Electrons move randomly with a net drift opposite to the electric field.

Question 3

A wire of length $$L$$ and cross-sectional area $$A$$ has resistivity $$\rho. $$What is the resistance $$R of $$the wire?

Accepted Answer

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

Question 4

Which of the following best describes Ohm’s Law for an ohmic material?

Accepted Answer

$$V = IR$$

Question 5

A battery with emf $$\mathcal{E}$$ and internal resistance $$r is $$connected to a load resistance $$R. $$What is the current $$I in $$the circuit?

Accepted Answer

$$I = \frac{\mathcal{E}}{R + r}$$

Question 6

Which material listed below is a superconductor at low temperatures, as indicated by a sudden drop in resistance to zero at a critical temperature $$T_c$$?

Accepted Answer

Oxide of Thallium

Question 7

What is the SI unit of resistivity?

Accepted Answer

$$\Omega \cdot m$$

Question 8

If the current density $$J in a $$conductor is uniform and perpendicular to the area $$A$$, which equation correctly relates $$J$$, $$I$$, $$n$$, $$q$$, and $$v_d$$?

Accepted Answer

$$J = \frac{I}{A} = n q v_d$$

Question 9

A light bulb is rated at 120 V and 75 W. What is its resistance?

Accepted Answer

$$R = \frac{V^2$}{P} = \frac{(120)^2$}{75} \approx 192\ \Omega$$

Question 10

Which statement about the direction of electric current in a conductor is correct?

Accepted Answer

The direction of current is defined as the direction of flow of positive charges.

Question 11

A resistor’s value is marked by colored bands. If the first two bands are red and violet, and the third band is yellow, what is the resistance value?

Accepted Answer

$$27 	imes 10^4$\ \Omega = 270,000\ \Omega$$

Question 12

Which equation describes the temperature dependence of resistivity for most metals?

Accepted Answer

$$\rho = \$$rho_0$$ [1 + \alpha (T - T_0$)]$$

Question 13

Which device is used to measure current in a circuit and has negligible internal resistance?

Accepted Answer

Ammeter

Question 14

A battery with emf $$\mathcal{E}$$ and internal resistance $$r is $$short-circuited (external resistance $$R = 0). $$What is the terminal voltage?

Accepted Answer

$$V = 0$$

Question 15

Which material listed below is a semiconductor, exhibiting a decrease in resistivity with increasing temperature?

Accepted Answer

Silicon

Question 16

What is the power $$P$$ dissipated in a resistor $$R$$ when a current $$I$$ flows through it?

Accepted Answer

$$P = I^2$ R$$

Question 17

Which equation gives the drift velocity $$v_d of $$charge carriers in a conductor, given current $$I$$, charge carrier density $$n$$, charge $$q$$, and cross-sectional area $$A$$?

Accepted Answer

$$v_d = \frac{I}{n q A}$$

Question 18

Which statement best explains why power companies transmit electricity at high voltages and low currents?

Accepted Answer

To minimize power losses due to resistance in transmission lines.

Question 19

If a conductor obeys Ohm’s Law, which relationship between current density $$J$$ and electric field $$E is $$correct?

Accepted Answer

$$J = \sigma E$$

Question 20

A resistor is heated by a current. Which form of energy is primarily responsible for the increase in temperature of the resistor?

Accepted Answer

Internal energy due to collisions between electrons and atoms.

Current, Resistance, and Electromotive Force (EMF): Study Notes

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