5.2 Heating Effect

A copper wire has a resistance of R at room temperature. If the temperature of the wire is increased, what will happen to its resistance?

A. Remains the same

B. Decreases

C. Increases

D. Becomes zero

Which of the following materials has the highest resistivity at room temperature?

A. Silver

B. Copper

C. Iron

D. Rubber

According to Ohm's law, if the voltage across a resistor is doubled, the current through it will:

A. Remain the same

B. Be halved

C. Be doubled

D. Be quadrupled

A device consumes 60W of power when connected to a 240V supply. What is the resistance of the device?

A. 960 ohms

B. 480 ohms

C. 240 ohms

D. 120 ohms

Which of the following is NOT a limitation of Ohm's law?

A. It does not apply to non-linear devices.

B. It does not apply at very high frequencies.

C. It does not apply to superconductors.

D. It does not apply to resistors.

a) Define Ohm's law and state its mathematical expression. [2]

b) A resistor has a constant voltage of 12 V applied across it and carries a current of 3 A. Calculate its resistance using Ohm's law. [3]

a) Explain the concept of resistivity and how it differs from resistance. [3]

b) A copper wire has a length of 2 m, a cross-sectional area of 1 x 10^-6 m^2, and a resistance of 0.1 ohms. Calculate its resistivity. [2]

a) Define electric power and state its relation to voltage and current. [2]

b) A device operates on a voltage of 230 V and draws a current of 5 A. Calculate the power consumed by the device. [3]

a) Describe the relationship between current, resistance, and the heat produced in a resistor. [3]

b) A 10-ohm resistor has a current of 2 A flowing through it. Calculate the heat produced in the resistor in 5 seconds. [3]

c) How would the heat produced change if the current is doubled? [2]

a) Define resistivity and state its unit. [2]

b) A material has a resistance of 8 ohms when its length is 2 m and its cross-sectional area is 2 x 10^-6 m^2. Calculate its resistivity. [3]

c) How would the resistance change if the length of the material is halved while keeping the cross-sectional area constant? [2]