Q: A toaster is rated at 1200 W and operates at 120 V. What is the current drawn by the toaster?

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

Q: The root mean square (rms) value of an AC current $$I_0 is $$given by:

$$I_{\text{rms}} = \frac{I_0$}{\sqrt{2}}$$

Question 1

A battery is used to power a flashlight. Which statement best describes the role of the battery in the circuit?

Accepted Answer

It maintains a constant potential difference across its terminals, transforming chemical energy into electrical energy.

Question 2

Which equation correctly defines electric current $$I in $$terms of charge $$Q$$ and time $$t$$?

Accepted Answer

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

Question 3

A copper wire has a length $$L$$ and cross-sectional area $$A. $$Its resistance $$R is $$given by which formula?

Accepted Answer

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

Question 4

A toaster is rated at 1200 W and operates at 120 V. What is the current drawn by the toaster?

Accepted Answer

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

Question 5

Which of the following statements about Ohm’s law is correct?

Accepted Answer

Ohm’s law states that the current through a conductor is proportional to the potential difference across it, provided the resistance is constant.

Question 6

A wire made of a material with resistivity $$ho is $$heated from $$20^\circ	ext{C} to$$ $$80^\circ	ext{C}. $$What happens to its resistance?

Accepted Answer

The resistance increases because resistivity increases with temperature for most materials.

Question 7

Which formula gives the electric power $$P$$ dissipated in a resistor with resistance $$R$$ and current $$I$$?

Accepted Answer

$$P = I^2$ R$$

Question 8

A household circuit uses a fuse rated at 15 A. If three appliances are connected, each drawing 6 A, what will happen?

Accepted Answer

The fuse will blow because the total current is 18 A, which exceeds the fuse rating.

Question 9

Which equation describes the time-varying voltage in an alternating current (AC) circuit?

Accepted Answer

$$V = V_0$ \sin(\omega t)$$

Question 10

The root mean square (rms) value of an AC current $$I_0 is $$given by:

Accepted Answer

$$I_{	ext{rms}} = \frac{I_0$}{\sqrt{2}}$$

Question 11

A hospital uses a superconducting magnet for MRI imaging. What is a key property of superconductors relevant to this application?

Accepted Answer

They have zero resistance below their critical temperature, allowing persistent currents.

Question 12

In the microscopic view of electric current, what is the drift velocity $$v_d of $$electrons related to?

Accepted Answer

It is related to the current $$I$$ and the number of charge carriers per unit volume.

Question 13

Which statement best describes the direction of conventional current in a circuit?

Accepted Answer

It flows from the positive terminal to the negative terminal.

Question 14

A neuron transmits an electrical signal along its axon. What is the primary mechanism for this conduction?

Accepted Answer

Propagation of an action potential due to ion movement across the cell membrane.

Question 15

A 100 W light bulb is left on for 10 hours. How much energy is consumed, in kilowatt-hours (kWh)?

Accepted Answer

$$	ext{Energy} = \frac{100}{1000} 	imes 10 = 1\ 	ext{kWh}$$

Question 16

Which of the following is NOT a property of ohmic materials?

Accepted Answer

Their resistance changes with the direction of current.

Question 17

A wire has resistance $$R at$$ $$20^\circ	ext{C}. If $$its temperature coefficient is $$\alpha$$, what is its resistance $$R_T at $$temperature $$T$$?

Accepted Answer

$$R_T = R[1 + \alpha (T - 20)]$$

Question 18

Which of the following best explains why circuit breakers are preferred over fuses in modern homes?

Accepted Answer

Circuit breakers can be reset after tripping, while fuses must be replaced.

Question 19

A student connects a battery, a resistor, and a wire to form a circuit. Which statement is true about the flow of charge?

Accepted Answer

Whatever charge enters one end of the circuit exits the other end; charge is not used up.

Chapter 18: Electric Currents – Study Notes

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