Gaokao Exam Gaokao Physics: Electromagnetism 4 — Questions and Answers
Question 1: Three resistors of 6 Ω, 3 Ω, and 2 Ω are connected in parallel. What is the equivalent resistance?
- 1 Ω (Correct answer)
- 11 Ω
- 2 Ω
- 0.5 Ω
Correct answer: 1 Ω
1/R = 1/6 + 1/3 + 1/2 = 1/6 + 2/6 + 3/6 = 1; R = 1 Ω.
Question 2: A wire of resistance R is stretched to twice its original length. Its new resistance is:
- 4R (Correct answer)
- 2R
- R/2
- R/4
Correct answer: 4R
Stretching to twice the length doubles L and halves cross-sectional area A (volume conserved); R = ρL/A increases by factor 4.
Question 3: A uniform electric field E = 500 V/m exists between two parallel plates separated by d = 0.02 m. The potential difference between the plates is:
- 10 V (Correct answer)
- 25 V
- 100 V
- 250 V
Correct answer: 10 V
V = Ed = 500 × 0.02 = 10 V.
Question 4: According to the right-hand screw rule, the magnetic field lines around a straight current-carrying wire form:
- Concentric circles in planes perpendicular to the wire (Correct answer)
- Straight lines parallel to the wire
- Radial lines pointing away from the wire
- Helical patterns along the wire
Correct answer: Concentric circles in planes perpendicular to the wire
By Ampere's law, the magnetic field around a long straight wire forms closed circular loops centred on the wire.
Question 5: Electromagnetic induction was discovered experimentally by:
- Michael Faraday (Correct answer)
- James Clerk Maxwell
- Heinrich Hertz
- André-Marie Ampère
Correct answer: Michael Faraday
Faraday discovered electromagnetic induction in 1831 through experiments with changing magnetic flux.
Question 6: A 60 W light bulb operates on a 120 V AC supply. The resistance of the filament during operation is:
- 240 Ω (Correct answer)
- 120 Ω
- 60 Ω
- 480 Ω
Correct answer: 240 Ω
P = V²/R → R = V²/P = 120²/60 = 240 Ω.
Question 7: The work done in moving a charge of +3 μC from a point at potential 20 V to a point at potential 80 V is:
- 1.8×10⁻⁴ J (Correct answer)
- −1.8×10⁻⁴ J
- 2.4×10⁻⁴ J
- 6.0×10⁻⁴ J
Correct answer: 1.8×10⁻⁴ J
W = q(V₂ − V₁) = 3×10⁻⁶ × (80 − 20) = 3×10⁻⁶ × 60 = 1.8×10⁻⁴ J.
Gaokao Exam Gaokao Physics: Electromagnetism 4
Three resistors of 6 Ω, 3 Ω, and 2 Ω are connected in parallel.
What is the equivalent resistance?