NUMS — Medical & Dental Entry Test

NUMS Physics — Electricity and Magnetism (Set 3)

Take the NUMS Physics — Electricity and Magnetism (Set 3): 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 point charges of +2.0 μC each are placed 3.0 cm apart in air. What is the force between them? (k = 9 × 10⁹ N m² C⁻²)
- A. 4.0 N
- B. 40 N ✓
- C. 1200 N
- D. 13 N
Answer: B. 40 N
Explanation: F = kq₁q₂/r² = 9 × 10⁹ × (2 × 10⁻⁶)²/(0.03)² = 40 N (repulsive).
Q2. What is the magnitude of the electric field at a distance of 0.30 m from a point charge of 3.0 nC? (k = 9 × 10⁹ N m² C⁻²)
- A. 300 N/C ✓
- B. 90 N/C
- C. 900 N/C
- D. 30 N/C
Answer: A. 300 N/C
Explanation: E = kq/r² = 9 × 10⁹ × 3 × 10⁻⁹/0.09 = 300 N/C.
Q3. An electron is placed between two parallel plates 1.0 cm apart with a potential difference of 200 V. What is its acceleration? (e = 1.6 × 10⁻¹⁹ C, m = 9.11 × 10⁻³¹ kg)
- A. 3.5 × 10¹⁵ m/s² ✓
- B. 1.8 × 10¹⁵ m/s²
- C. 3.5 × 10¹³ m/s²
- D. 7.0 × 10¹⁵ m/s²
Answer: A. 3.5 × 10¹⁵ m/s²
Explanation: E = V/d = 2 × 10⁴ V/m; a = eE/m = (1.6 × 10⁻¹⁹ × 2 × 10⁴)/(9.11 × 10⁻³¹) = 3.51e+15 m/s².
Q4. An electron starting from rest is accelerated through a potential difference of 100 V. What is its final speed? (e = 1.6 × 10⁻¹⁹ C, m = 9.11 × 10⁻³¹ kg)
- A. 5.9 × 10⁴ m/s
- B. 5.93 × 10⁶ m/s ✓
- C. 8.4 × 10⁶ m/s
- D. 3.5 × 10⁷ m/s
Answer: B. 5.93 × 10⁶ m/s
Explanation: ½mv² = eV gives v = √(2eV/m) = √(2 × 1.6 × 10⁻¹⁹ × 100/9.11 × 10⁻³¹) = 5.93 × 10⁶ m/s.
Q5. A point charge of 6.0 μC is placed at the centre of a cube. What is the electric flux through one face of the cube? (ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²)
- A. 6.8 × 10⁶ N m²/C
- B. 6.8 × 10⁵ N m²/C
- C. 1.1 × 10⁵ N m²/C ✓
- D. 1.1 × 10⁶ N m²/C
Answer: C. 1.1 × 10⁵ N m²/C
Explanation: By symmetry each of the 6 faces gets one-sixth of the total flux: q/6ε₀ = 6.0 × 10⁻⁶/(6 × 8.85 × 10⁻¹²) = 1.1 × 10⁵ N m² C⁻¹.

The other 25 questions

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Q6. An air-filled parallel-plate capacitor has a capacitance of 12 pF. If the plate area is doubled and the plate separation is tripled, what is the new capacitance?
- A. 4 pF
- B. 72 pF
- C. 8 pF
- D. 18 pF
Q7. A 4 μF capacitor charged to 100 V is disconnected from the supply and connected in parallel with an uncharged 6 μF capacitor. What is the common potential difference?
- A. 60 V
- B. 40 V
- C. 100 V
- D. 50 V
Q8. A capacitor is charged and then disconnected from the battery. A dielectric slab of dielectric constant 4 is then inserted fully between the plates. What happens to the stored energy?
- A. It remains unchanged
- B. It becomes one-quarter of its original value
- C. It becomes half of its original value
- D. It becomes four times the original value
Q9. In the circuit, a 5 Ω resistor is in series with a parallel combination of 4 Ω and 12 Ω resistors, connected to a 16 V battery of negligible internal resistance. What current flows through the 4 Ω resistor?
- A. 2.0 A
- B. 1.5 A
- C. 4.0 A
- D. 0.5 A
Q10. A uniform wire is stretched to twice its original length with its volume remaining constant. What happens to its resistance?
- A. It becomes four times as large
- B. It becomes twice as large
- C. It becomes half as large
- D. It stays the same
Q11. What is the resistance of a nichrome wire 2.0 m long with a cross-sectional area of 0.50 mm²? (ρ = 1.1 × 10⁻⁶ Ω m)
- A. 44 Ω
- B. 1.1 Ω
- C. 0.44 Ω
- D. 4.4 Ω
Q12. A copper coil has a resistance of 10 Ω at 20 °C. What is its resistance at 70 °C if the temperature coefficient of resistance is 0.004 °C⁻¹?
- A. 14 Ω
- B. 10.2 Ω
- C. 8 Ω
- D. 12 Ω
Q13. A battery of EMF 9.0 V delivers 0.90 A to an external resistor, and the voltage across its terminals is 8.1 V. What is the internal resistance of the battery?
- A. 10 Ω
- B. 9.0 Ω
- C. 1.0 Ω
- D. 0.90 Ω
Q14. Two batteries of EMF 10 V and 4 V with negligible internal resistance are connected in opposition in a single loop that has a total resistance of 3 Ω. What current flows?
- A. 14 A
- B. 2 A
- C. 4.7 A
- D. 1 A
Q15. A bulb is marked 100 W, 220 V. If it is run on a 110 V supply, what power does it dissipate (assuming its resistance is unchanged)?
- A. 50 W
- B. 100 W
- C. 25 W
- D. 12.5 W
Q16. A 2 kW heater is used for 3 hours every day for 30 days. If one unit (kWh) costs Rs 30, what is the monthly cost?
- A. Rs 5400
- B. Rs 2700
- C. Rs 1800
- D. Rs 180
Q17. A balanced Wheatstone bridge satisfies P/Q = R/S. If P = 10 Ω, Q = 20 Ω and R = 30 Ω, what is the unknown resistance S?
- A. 40 Ω
- B. 6.7 Ω
- C. 15 Ω
- D. 60 Ω
Q18. An electron moving at 2.0 × 10⁶ m/s enters a uniform magnetic field of 0.010 T at right angles to the field. What is the radius of its circular path?
- A. 1.14 mm
- B. 0.114 mm
- C. 11.4 mm
- D. 2.28 mm
Q19. A straight wire 0.50 m long carries 4.0 A at an angle of 30° to a uniform magnetic field of 0.20 T. What is the magnetic force on the wire?
- A. 0.35 N
- B. 0.40 N
- C. 0.20 N
- D. 0.10 N
Q20. A solenoid has 500 turns uniformly wound on a length of 25 cm and carries a current of 2.0 A. What is the magnetic field inside it near the centre? (μ₀ = 4π × 10⁻⁷ T m/A)
- A. 5.0 × 10⁻³ T
- B. 2.5 × 10⁻⁵ T
- C. 1.3 × 10⁻³ T
- D. 6.3 × 10⁻⁷ T
Q21. Two long parallel wires 10 cm apart carry currents of 10 A and 5 A in the same direction. What is the force per metre between them? (μ₀/2π = 2 × 10⁻⁷ T m/A)
- A. 1.0 × 10⁻⁵ N/m, attractive
- B. 1.0 × 10⁻⁴ N/m, attractive
- C. 1.0 × 10⁻⁴ N/m, repulsive
- D. 5.0 × 10⁻⁴ N/m, attractive
Q22. A galvanometer of resistance 50 Ω gives full-scale deflection for 2.0 mA. What series resistance is needed to convert it into a voltmeter reading 0–10 V?
- A. 5000 Ω
- B. 4.95 Ω
- C. 4950 Ω
- D. 250 Ω
Q23. The magnetic flux through a coil of 100 turns changes from 0.050 Wb to 0.010 Wb in 0.20 s. What is the magnitude of the average induced EMF?
- A. 0.2 V
- B. 8 V
- C. 2 V
- D. 20 V
Q24. A conducting rod 0.50 m long moves at 4.0 m/s perpendicular to a uniform magnetic field of 0.30 T. What EMF is induced across the rod's ends?
- A. 0.15 V
- B. 0.60 V
- C. 2.4 V
- D. 1.2 V
Q25. The north pole of a bar magnet is pushed towards a coil. What is the polarity of the coil face nearest the magnet, according to Lenz's law?
- A. North, to increase the flux
- B. No polarity is induced because the magnet is stationary relative to the coil
- C. South, to attract the magnet
- D. North, to oppose the approach of the magnet
Q26. A coil of self-inductance 2.0 H carries a steady current of 4.0 A. How much energy is stored in its magnetic field?
- A. 8 J
- B. 4 J
- C. 16 J
- D. 32 J
Q27. An ideal transformer has 1000 turns in the primary and 50 turns in the secondary, with 220 V applied to the primary. If the secondary delivers 100 W, what current flows in the primary?
- A. 0.023 A
- B. 9.1 A
- C. 0.45 A
- D. 2.0 A
Q28. What is the resonant frequency of a series LC circuit with L = 1.0 mH and C = 10 μF?
- A. 159 Hz
- B. 16 000 Hz
- C. 1592 Hz
- D. 10 000 Hz
Q29. A 1.0 MΩ resistor charges a 2.0 μF capacitor from a 10 V supply. What is the potential difference across the capacitor after one time constant?
- A. 6.3 V
- B. 5.0 V
- C. 10 V
- D. 3.7 V
Q30. Why is the iron core of a transformer made of thin laminated sheets insulated from each other?
- A. To increase the number of turns possible
- B. To reduce energy loss from eddy currents
- C. To raise the voltage of the secondary
- D. To prevent magnetisation of the core