An electric bulb is connected to a 110 V generator. The current is 0.2 A. What is the power of the bulb?
- A.0.22 W
- B.2.2 W
- C.22 W
- D.220 W
Correct answer
Explanation
The correct answer is C, 22 W. Electric power is voltage multiplied by current, and 110 V × 0.2 A = 22 W.
Power is the rate at which electrical energy is used. For any device, P = VI, where V is the potential difference across it in volts and I the current through it in amperes; the answer comes out in watts. The same relation can be written as P = I²R or P = V²/R using Ohm's law. One watt means one joule of energy used every second, and one kilowatt-hour (the household "unit") is 1000 W used for an hour.
A is wrong: 0.22 W is a hundred times too small; the decimal has been misplaced.
B is wrong: 2.2 W is ten times too small.
D is wrong: 220 W would need a current of 2 A at 110 V.
Exam tip: P = VI; one kilowatt-hour equals 3.6 × 10⁶ joules.
Practice Questions
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- B.It is neutral
- C.It is basic
- D.It is made up of Calcium phosphate, the material of tooth enamel
Show answer
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- A.P' = P
- B.P' = 2P
- C.P' = P/2
- D.P' = P/4
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- B.Na⁺, O²⁻
- C.Al³⁺, Cl⁻
- D.K⁺, Ne
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- A.The disc
- B.The sphere
- C.Both have the same moment of inertia
- D.The information provided is not sufficient to answer the question
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- A.−40°
- B.0°
- C.−273°
- D.100°
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