Gaokao Exam Gaokao Physics: Electromagnetism 5 — Questions and Answers
Question 1: Two long parallel wires carry equal currents in the same direction. The magnetic force between them is:
- Attractive (Correct answer)
- Repulsive
- Zero
- Perpendicular to the wires
Correct answer: Attractive
Parallel currents in the same direction attract each other; this is the basis of the original SI definition of the ampere.
Question 2: A capacitor with capacitance 20 μF is connected to a DC source of 50 V. What charge is stored?
- 1×10⁻³ C (Correct answer)
- 2.5×10⁻⁴ C
- 4×10⁻³ C
- 5×10⁻⁴ C
Correct answer: 1×10⁻³ C
Q = CV = 20×10⁻⁶ × 50 = 1×10⁻³ C.
Question 3: In a solenoid, doubling the number of turns per unit length (while keeping current constant) changes the magnetic field inside by a factor of:
- 2 (Correct answer)
- 4
- √2
- 1/2
Correct answer: 2
B = μ₀nI; doubling n doubles B.
Question 4: The unit of magnetic flux is:
- Weber (Wb) (Correct answer)
- Tesla (T)
- Henry (H)
- Farad (F)
Correct answer: Weber (Wb)
Magnetic flux Φ = BA is measured in Webers (Wb); 1 Wb = 1 T·m².
Question 5: A positive charge moves in the direction of an electric field. Its electric potential energy:
- Decreases (Correct answer)
- Increases
- Stays the same
- First increases then decreases
Correct answer: Decreases
A positive charge moving along the field direction loses potential energy (like a mass falling in gravity).
Question 6: A current of 5 A flows through a 10 Ω resistor for 2 minutes. The heat generated is:
- 30,000 J (Correct answer)
- 1,000 J
- 6,000 J
- 300 J
Correct answer: 30,000 J
Q = I²Rt = 25 × 10 × 120 = 30,000 J.
Question 7: Maxwell's equations predict that changing electric fields create:
- Magnetic fields (Correct answer)
- Gravitational fields
- Nuclear forces
- Static charge
Correct answer: Magnetic fields
Maxwell's displacement current concept shows that a time-varying electric field generates a magnetic field, just as a physical current does.
Gaokao Exam Gaokao Physics: Electromagnetism 5
Two long parallel wires carry equal currents in the same direction.
The magnetic force between them is: