A 40 W electric lamp is left ON continuously for 1,750 h. What is the total energy consumed, expressed in kilowatt-hours (kWh)?

Introduction:
Electric energy billing commonly uses the kilowatt-hour (kWh) unit. Converting power and operating time to energy is a routine calculation for estimating electricity usage and costs.

Given Data / Assumptions:

• Lamp power P = 40 W.
• Operating time t = 1,750 h.
• Constant power draw over the interval.

Concept / Approach:
Energy E = P * t. Convert the product to kWh by expressing power in kilowatts. 1 kW = 1,000 W and 1 kWh = energy used by 1 kW over 1 hour.

Step-by-Step Solution:
1) Convert power to kilowatts: 40 W = 0.040 kW.2) Multiply by time: E = 0.040 kW * 1,750 h.3) Compute: E = 70 kWh.4) Present result with proper unit: 70 kWh.

Verification / Alternative check:
Compute in watt-hours first: E = 40 W * 1,750 h = 70,000 Wh. Convert Wh to kWh by dividing by 1,000: 70,000 Wh / 1,000 = 70 kWh, matching the above.

Why Other Options Are Wrong:
43.75: Would correspond to 25 W or shorter time; does not match the given numbers.
43,750 and 70,000: These are Wh, not kWh (missing the divide-by-1,000 step).
7: Off by a factor of 10; likely a unit slip.

Common Pitfalls:
Forgetting to convert watts to kilowatts or interpreting Wh as kWh. Always check unit consistency: multiply kW by hours to get kWh.

Final Answer:
70