Home › UCE (O-Level) › Physics › Electric circuits › A lamp dissipates 60 watts and is left on for 12…
A lamp dissipates 60 watts and is left on for 120 seconds. How much electrical energy does it use?
A1800 joules
B7200 joules
C0.5 joules
D3600 joules
Answer & Solution
Correct answer: B. 7200 joules
1. Power measures how fast energy is transferred, so energy needs the time as well.
2. Electrical energy is simply power multiplied by time.
3. The power given is 60 watts and the time given is 120 seconds.
4. Multiplying gives 60 times 120, which is 7200.
5. Energy is measured in joules, so the lamp uses 7200 joules.
6. Dividing 60 by 120 gives 0.5, which is the trap for anyone who reaches for a division instead.
_Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 11: Electric circuits_
Related questions
Household electricity is sold in units of one kilowatt hour. What does one kilowatt hour mA current of 4 amperes passes through a heater while the voltage across it is 12 volts. WhHow is the equivalent resistance of several resistors joined in series worked out?Three resistors are connected side by side across the same cell. Which quantity is the samThree resistors are joined one after another in a single loop with a cell. How does the cuThe filament of a light bulb gets much hotter as the supply voltage rises, so its resistanOhm's law describes a metal conductor only while which quantity is held constant?