Electrical Energy and Power
Physics · 50 practice questions
Concepts and commercial units of electrical energy and power; electric power transmission; heating effects of electric current; electrical wiring of houses; use of fuses.
- Apply expressions of electrical energy and power to solve problems.
- Analyse power transmission from station to consumer.
- Identify heating effects of current and their uses.
- Determine fuse ratings and the advantages of parallel wiring.
Try a few questions
- Practice question 1
Electric power is transmitted over long distances using high voltage and low current mainly to
- A.maximize power loss in the transmission cables for safety
- B.reduce the total amount of energy actually delivered to consumers
- C.minimize power loss (I²R losses) in the transmission cables
- D.eliminate the need for any transformers along the transmission route
Show the answer
C. minimize power loss (I²R losses) in the transmission cables
Since power loss scales with the square of current, keeping current low (with high voltage) sharply cuts transmission losses.
- Practice question 2
A short circuit occurs when a fault provides
- A.a path of very low resistance for current to flow, resulting in a dangerously high current
- B.a path of very high resistance, resulting in almost no current flow at all
- C.a complete break in the circuit, stopping all current flow
- D.an alternative, perfectly safe route for current with no risk involved
Show the answer
A. a path of very low resistance for current to flow, resulting in a dangerously high current
The unusually low resistance of a short circuit allows a dangerously large current to flow, risking fire or damage.
- Practice question 3
Power dissipated in a resistor can also be calculated using the formula
- A.P = I/R
- B.P = R/I
- C.P = I²R
- D.P = I + R
Show the answer
C. P = I²R
This formula, derived by combining P = VI with Ohm's law (V = IR), gives power directly from current and resistance.
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