NUMS — Medical & Dental Entry Test

NUMS Physics — Electricity and Magnetism (Set 2)

Take the NUMS Physics — Electricity and Magnetism (Set 2): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review. Covers…

What this test covers

30 NUMS Physics

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. Two small spheres each carrying +1 μC are held 10 cm apart in air. What force does each exert on the other? (k = 9 × 10⁹ N m² C⁻²)
- A. 0.09 N, repulsive
- B. 0.9 N, repulsive ✓
- C. 9 N, attractive
- D. 0.9 N, attractive
Answer: B. 0.9 N, repulsive
Explanation: F = kq₁q₂/r² = 9 × 10⁹ × (10⁻⁶)² / (0.1)² = 0.9 N; like charges repel.
Q2. Two charges exert a force F on each other in air. They are placed in water (relative permittivity 80) at the same separation. What is the new force?
- A. 80F
- B. F/80 ✓
- C. F/√80
- D. F
Answer: B. F/80
Explanation: F = q₁q₂/(4πε₀εᵣr²), so the force is reduced by the factor εᵣ = 80. This is why water dissolves ionic salts so well.
Q3. Two parallel plates 4 mm apart are connected across a 200 V supply. What is the electric field strength between them?
- A. 5 × 10⁵ V m⁻¹
- B. 50 V m⁻¹
- C. 800 V m⁻¹
- D. 5 × 10⁴ V m⁻¹ ✓
Answer: D. 5 × 10⁴ V m⁻¹
Explanation: E = V/d = 200 / (4 × 10⁻³) = 5 × 10⁴ V m⁻¹.
Q4. An electron is placed in a uniform electric field of 1.0 × 10⁴ N C⁻¹. What is its acceleration? (e = 1.6 × 10⁻¹⁹ C, mₑ = 9.1 × 10⁻³¹ kg)
- A. 1.6 × 10⁻¹⁵ m s⁻²
- B. 1.76 × 10¹⁵ m s⁻² ✓
- C. 1.76 × 10¹¹ m s⁻²
- D. 5.7 × 10⁻¹⁶ m s⁻²
Answer: B. 1.76 × 10¹⁵ m s⁻²
Explanation: F = eE = 1.6 × 10⁻¹⁹ × 10⁴ = 1.6 × 10⁻¹⁵ N; a = F/m = 1.6 × 10⁻¹⁵ / 9.1 × 10⁻³¹ = 1.76 × 10¹⁵ m s⁻².
Q5. A closed surface encloses no charge, but a charge q lies just outside it. According to Gauss's law, what is the total electric flux through the closed surface?
- A. −q/ε₀
- B. q/ε₀
- C. Zero ✓
- D. q/2ε₀
Answer: C. Zero
Explanation: Flux through a closed surface equals (enclosed charge)/ε₀. Field lines from the outside charge enter and leave the surface equally, giving zero net flux.

The other 25 questions

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Q6. How much work is needed to bring a +2 μC charge from infinity to a point where the electric potential is 300 V?
- A. 6 × 10⁻⁴ J
- B. 6.7 × 10⁻⁹ J
- C. 6 × 10⁻² J
- D. 1.5 × 10² J
Q7. Capacitors of 3 μF and 6 μF are joined in series, and this pair is connected in parallel with a 4 μF capacitor. What is the equivalent capacitance?
- A. 1.33 μF
- B. 13 μF
- C. 2 μF
- D. 6 μF
Q8. A 10 μF capacitor is connected to a 12 V battery until fully charged. What charge is stored on it?
- A. 0.83 μC
- B. 120 μC
- C. 1.2 μC
- D. 720 μC
Q9. The separation between the plates of an isolated air-filled parallel-plate capacitor is doubled. What happens to its capacitance?
- A. It halves
- B. It doubles
- C. It becomes four times larger
- D. It stays the same
Q10. An uncharged capacitor is charged through a resistor from a battery. What fraction of its final charge does it hold after one time constant (t = RC)?
- A. About 63%
- B. 50%
- C. 100%
- D. About 37%
Q11. Free electrons in a copper wire drift at only about a millimetre per second, yet a lamp lights almost instantly when switched on. Why?
- A. Electrons travel at the speed of light once the switch closes
- B. Protons carry the current faster than electrons
- C. The lamp stores charge before it is switched on
- D. The electric field travels through the wire at nearly the speed of light, setting all electrons moving at once
Q12. The current–voltage graph of a filament lamp curves towards the voltage axis at higher voltages. What does this indicate?
- A. It obeys Ohm's law
- B. It is a semiconductor diode
- C. Its resistance decreases as the current increases
- D. Its resistance increases as its temperature rises
Q13. A copper wire 10 m long has a cross-sectional area of 1.0 mm². What is its resistance? (ρ of copper = 1.7 × 10⁻⁸ Ω m)
- A. 17 Ω
- B. 1.7 × 10⁻⁷ Ω
- C. 0.17 Ω
- D. 0.017 Ω
Q14. A carbon resistor has colour bands brown, black, red (followed by gold). What is its resistance?
- A. 102 Ω ± 5%
- B. 100 Ω ± 5%
- C. 1000 Ω ± 5%
- D. 10 000 Ω ± 5%
Q15. Three 6 Ω resistors are connected so that two are in parallel and this pair is in series with the third. What is the total resistance?
- A. 2 Ω
- B. 4 Ω
- C. 9 Ω
- D. 18 Ω
Q16. A 100 W bulb and a 60 W bulb, both rated for 220 V, are connected in series across a 220 V supply. Which glows brighter?
- A. Neither glows at all
- B. Both glow equally, as the same current flows
- C. The 60 W bulb, because it has the larger resistance
- D. The 100 W bulb, because it has the higher rating
Q17. A 2 kW electric heater in a clinic is used for 3 hours a day. How much electrical energy does it use per day?
- A. 6000 kWh
- B. 6 kWh
- C. 0.67 kWh
- D. 1.5 kWh
Q18. Kirchhoff's second (loop) rule states that the sum of emfs around a closed loop equals the sum of potential drops. This rule is based on the conservation of:
- A. momentum
- B. energy
- C. mass
- D. charge
Q19. In a potentiometer experiment a standard cell of emf 1.5 V is balanced at a length of 60 cm of the wire. A second cell is balanced at 80 cm. What is the emf of the second cell?
- A. 2.4 V
- B. 2.0 V
- C. 1.1 V
- D. 1.2 V
Q20. A battery of emf E and internal resistance r is connected to a variable load resistor R. For what value of R is the power delivered to the load a maximum?
- A. R = 0
- B. R = r
- C. R very large compared with r
- D. R = 2r
Q21. A platinum resistance thermometer has a resistance of 10 Ω at 0 °C and a temperature coefficient of resistance of 0.004 K⁻¹. What is its resistance at 100 °C?
- A. 4 Ω
- B. 10.4 Ω
- C. 40 Ω
- D. 14 Ω
Q22. A cable inside a hospital wall carries a steady current of 15 A. What is the magnetic field it produces 5.0 cm away? (μ₀ = 4π × 10⁻⁷ T m A⁻¹)
- A. 6.0 × 10⁻³ T
- B. 1.2 × 10⁻⁴ T
- C. 3.8 × 10⁻⁴ T
- D. 6.0 × 10⁻⁵ T
Q23. A long solenoid is rewound with twice as many turns over the same length, and the current through it is halved. What happens to the magnetic field inside it?
- A. It stays the same
- B. It halves
- C. It becomes four times larger
- D. It doubles
Q24. In a cyclotron, a proton circulates in a uniform magnetic field. As it speeds up, how does its time for one revolution change (non-relativistic case)?
- A. It decreases, because the speed increases
- B. It increases, because the radius increases
- C. It doubles each revolution
- D. It stays the same, because T = 2πm/(qB) does not depend on speed
Q25. A rectangular coil of 100 turns, area 4.0 × 10⁻⁴ m², carries 0.50 A in a radial field of 0.50 T. What maximum torque acts on it?
- A. 1 × 10⁻⁴ N m
- B. 0.01 N m
- C. 2.5 N m
- D. 0.1 N m
Q26. A galvanometer of resistance 50 Ω gives full-scale deflection at 1.0 mA. What resistance must be connected in series with it to make a voltmeter reading up to 10 V?
- A. 9.95 Ω
- B. 9950 Ω
- C. 10 000 Ω
- D. 0.005 Ω
Q27. An aircraft with a wingspan of 40 m flies horizontally at 250 m s⁻¹ where the vertical component of Earth's magnetic field is 5.0 × 10⁻⁵ T. What emf is induced between its wingtips?
- A. 0.50 V
- B. 5.0 V
- C. 0.050 V
- D. 2.0 × 10⁻³ V
Q28. A coil of self-inductance 50 mH carries a steady current of 4.0 A. How much energy is stored in its magnetic field?
- A. 0.20 J
- B. 0.10 J
- C. 400 J
- D. 0.40 J
Q29. An AC generator coil has 50 turns of area 0.01 m² and rotates at 100 rad s⁻¹ in a field of 0.4 T. What is the peak emf?
- A. 20 V
- B. 200 V
- C. 2 V
- D. 0.2 V
Q30. What is the reactance of a pure 0.10 H inductor connected to the 50 Hz mains?
- A. 5.0 Ω
- B. 3.14 Ω
- C. 0.032 Ω
- D. 31.4 Ω