Question

A bulb of 60 watt runs for 50 hours. How much electrical energy is consumed ?

• A. 3 kWh
• B. 4 kWh
• C. 10 kWh
• D. 12 kWh

Hint:

Energy = Power \(\times\) Time. 1. Power \(P = 60\) W. Time \(t = 50\) hours. 2. Calculate energy in Watt-hours (Wh): Energy = \(60 \text{ W} \times 50 \text{ h} = 3000 \text{ Wh}\). 3. Convert Watt-hours to kilowatt-hours (kWh): Since \(1 \text{ kWh} = 1000 \text{ Wh}\), divide by 1000. Energy = \(\frac{3000 \text{ Wh}}{1000} = 3 \text{ kWh}\). Alternatively, convert Power to kW first: \(60 \text{ W} = 0.06 \text{ kW}\). Then Energy = \(0.06 \text{ kW} \times 50 \text{ h} = 3 \text{ kWh}\).

Answer 1

The Correct Option is A

Concept: Electrical energy consumed is calculated by multiplying the power of the appliance by the time for which it is used. Energy (\(E\)) = Power (\(P\)) \(\times\) Time (\(t\)). If power is in watts (W) and time is in hours (h), the energy will be in watt-hours (Wh). If power is in kilowatts (kW) and time is in hours (h), the energy will be in kilowatt-hours (kWh). 1 kilowatt (kW) = 1000 watts (W). Step 1: Identify the given values
Power of the bulb, \(P = 60 \text{ watt (W)}\)
Time for which it runs, \(t = 50 \text{ hours (h)}\) The options are in kWh, so it's convenient to convert power to kilowatts first. Step 2: Convert power from watts to kilowatts \[ P = 60 \text{ W} = \frac{60}{1000} \text{ kW} = 0.06 \text{ kW} \] Step 3: Calculate the electrical energy consumed in kWh Using the formula \(E = P \times t\): \[ E = (0.06 \text{ kW}) \times (50 \text{ h}) \] \[ E = 0.06 \times 50 \text{ kWh} \] \[ E = \frac{6}{100} \times 50 \text{ kWh} \] \[ E = \frac{6 \times 50}{100} \text{ kWh} \] \[ E = \frac{300}{100} \text{ kWh} \] \[ E = 3 \text{ kWh} \] Alternative calculation in Watt-hours first: Energy in Wh = \(60 \text{ W} \times 50 \text{ h} = 3000 \text{ Wh}\). To convert Wh to kWh, divide by 1000 (since 1 kWh = 1000 Wh): Energy in kWh = \(\frac{3000 \text{ Wh}}{1000} = 3 \text{ kWh}\). The electrical energy consumed is 3 kWh. This matches option (1).