**Electricity Worksheet-4**

- Calculate the potential difference required across a conductor of resistance 5 Ω to make a current of 1.5 A flow through it.

- A torch bulb has 1 Ω resistance. It draws a current of 0.3 A when glowing from a source of 3 V. calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance.

- How much current does an electric heater draw from a 220 V line, if the resistance of the heater (when hot) is 50 Ω?

- How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V?

- An incandescent lamp of resistance 80 Ω draws a current of 0.75 A. Find the line voltage.

- A current of 0.2 A flows through a conductor of resistance 4.5 Ω. Calculate the potential difference at the ends of the conductor.

- A bulb of resistance 400 Ω is connected to 220 V mains. Calculate the magnitude of current.

- An electric heater draws a current of 5 A when connected to 220 V mains. Calculate the resistance of its filament.

- How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω?

- The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V?

**Answer:**

- Resistance of the conductor, R = 5 Ω

Required current, I = 1.5 A

If V is the potential difference required across the conductor, then

V = IR = 1.5 × 5 = 7.5 V

- Potential difference, V = 3 volt

Current through the bulb when glowing, I = 0.3 A

Resistance of the bulb when glowing,

The resistance of the filament of the bulb increases from 1 Ω to 10 Ω (when it becomes hot and glows) because of an increase in its temperature.

- Potential difference, V = 220 V

Resistance of the heater, R = 50 Ω

Using ohm’s law,

- I = V/R = 220/400 = 0.55 A

- R = V/I = 220/5 = 44 Ω

- Resistance of the electric heater,

Changed potential difference V' = 120 V

Changed current, i.e.,

Since R remains the same, by doubling the potential difference, the current is also doubled, i.e., becomes 8 A as I ∝ V.