Question

An electric tungsten bulb is connected into a home circuit. The home electric supply runs at 220 volt potential difference. When switched on, a current of 0.45 A flows through the bulb. What must be the power (wattage) of the bulb? If it is kept ‘on’ for 10 hours, how many units of electricity will be consumed?

Hint:

Remember: Power is calculated as P = V × I, and energy is E = P × t. 1 unit of electricity = 1 kWh.

Answer 1

The power consumed by an electrical device can be calculated using the formula: P = V × I Where:
- P is the power in watts,
- V is the voltage in volts,
- I is the current in amperes.
Given that the voltage V = 220 volts and the current I = 0.45 A, we can calculate the power: P = 220 V × 0.45 A = 99 W Thus, the power of the bulb is 99 watts.
To find the units of electricity consumed, we use the formula for energy: E = P × t Where:
- E is the energy consumed in watt-hours (Wh),
- P is the power in watts,
- t is the time in hours.
The time is given as t = 10 hours, and the power is P = 99 watts. Therefore, the energy consumed is: E = 99 W × 10 h = 990 Wh Now, 1 unit of electricity is equal to 1 kilowatt-hour (kWh), so we convert watt-hours to kilowatt-hours: Energy in units = 990 Wh1000 = 0.99 kWh Thus, the electricity consumed in 10 hours is 0.99 units.