NUMS — Medical & Dental Entry Test

NUMS Physics — Electricity and Magnetism (Set 7)

Take the NUMS Physics — Electricity and Magnetism (Set 7): 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 identical small metal spheres carry charges +6.0 μC and −2.0 μC. They are touched together and then placed 0.20 m apart. What is the force between them? (k = 9.0 × 10⁹ N m² C⁻²)
- A. 0.9 N, repulsive ✓
- B. 3.6 N, repulsive
- C. 2.7 N, repulsive
- D. 0.9 N, attractive
Answer: A. 0.9 N, repulsive
Explanation: After contact the net charge +4.0 μC is shared equally: +2.0 μC each. F = kq²/r² = 9 × 10⁹ × (2 × 10⁻⁶)²/0.04 = 0.9 N; like charges repel.
Q2. A large uniformly charged insulating sheet carries a surface charge density of 2.0 μC m⁻². Using ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻², what is the electric field near its surface (away from the edges)?
- A. 5.65 × 10⁴ N C⁻¹
- B. 2.26 × 10⁻⁷ N C⁻¹
- C. 2.26 × 10⁵ N C⁻¹
- D. 1.13 × 10⁵ N C⁻¹ ✓
Answer: D. 1.13 × 10⁵ N C⁻¹
Explanation: For an infinite sheet E = σ/2ε₀ = 2.0 × 10⁻⁶/(2 × 8.85 × 10⁻¹²) = 1.13 × 10⁵ N C⁻¹, independent of distance.
Q3. A 2.0 μF and a 4.0 μF capacitor are connected in parallel across a 50 V supply. What is the total energy stored by the pair?
- A. 15.0 mJ
- B. 5.0 mJ
- C. 7.5 mJ ✓
- D. 2.5 mJ
Answer: C. 7.5 mJ
Explanation: C_parallel = 6.0 μF; U = ½CV² = ½ × 6.0 × 10⁻⁶ × 50² = 7.5 mJ (it is the sum ½ × 2 × 2500 + ½ × 4 × 2500 μJ = 2.5 + 5.0 mJ).
Q4. A 4.0 μF capacitor charged to 100 V is connected across an uncharged 6.0 μF capacitor. How much energy is lost (mainly as heat and radiation) in the process?
- A. 20 mJ
- B. 0 mJ
- C. 12 mJ ✓
- D. 8 mJ
Answer: C. 12 mJ
Explanation: Initial energy = ½ × 4.0 × 10⁻⁶ × 100² = 20 mJ. Charge 400 μC is shared over 10 μF: V = 40 V; final energy = ½ × 10 × 10⁻⁶ × 40² = 8 mJ. Loss = 20 − 8 = 12 mJ.
Q5. A parallel-plate capacitor is charged and then disconnected from the battery. A dielectric slab of constant 3 is then inserted to fill the gap. What happens to the stored energy and the electric field between the plates?
- A. Energy falls to one-third and field stays the same
- B. Energy stays the same and field falls to one-third
- C. Energy triples and field stays the same
- D. Energy and field both fall to one-third ✓
Answer: D. Energy and field both fall to one-third
Explanation: The charge is fixed. C becomes 3C, so U = Q²/2C falls to one-third; E = E₀/k also falls to one-third. (Work is done by the field pulling the slab in.)

The other 25 questions

Take the timed test (free, no sign-up) to see your score and the answer and explanation for every question.

Q6. A wire of resistance R is drawn through a die so that its length becomes three times the original, with no change in volume or resistivity. What is its new resistance?
- A. 27R
- B. 9R
- C. 3R
- D. R/3
Q7. A 6 Ω and a 3 Ω resistor are connected in parallel; this pair is in series with a 4 Ω resistor; and the whole combination is in parallel with a 3 Ω resistor. What is the total resistance?
- A. 3 Ω
- B. 6 Ω
- C. 4 Ω
- D. 2 Ω
Q8. A 12 V battery (internal resistance 1.0 Ω) and a 6.0 V battery (internal resistance 1.0 Ω) are connected in opposition, positive to positive, through a 4.0 Ω resistor in series. What current flows?
- A. 1.0 A
- B. 2.0 A
- C. 3.0 A
- D. 0.5 A
Q9. A 9.0 V battery of internal resistance 1.5 Ω drives a current through a 7.5 Ω resistor. What is the potential difference across the battery terminals?
- A. 6.0 V
- B. 7.5 V
- C. 9.0 V
- D. 8.0 V
Q10. A heater is rated 2000 W at 220 V. If the supply voltage drops to 110 V, what power does it dissipate (assuming constant resistance)?
- A. 250 W
- B. 2000 W
- C. 1000 W
- D. 500 W
Q11. In a potentiometer experiment a cell of EMF 1.50 V balances at 50 cm of the wire, and a second cell balances at 75 cm with the same driver current. What is the EMF of the second cell?
- A. 1.50 V
- B. 2.25 V
- C. 1.00 V
- D. 1.88 V
Q12. A galvanometer of resistance 100 Ω gives full-scale deflection for 1.0 mA. What shunt resistance is needed to convert it to an ammeter reading up to 100 mA?
- A. 10.1 Ω
- B. 1.00 Ω
- C. 0.10 Ω
- D. 1.01 Ω
Q13. Two long straight parallel wires 20 cm apart carry currents of 15 A and 10 A in the same direction. What is the force on a 2.0 m length of one wire, and is it attractive or repulsive? (μ₀ = 4π × 10⁻⁷ T m A⁻¹)
- A. 6.0 × 10⁻⁴ N, attractive
- B. 3.0 × 10⁻⁴ N, repulsive
- C. 1.5 × 10⁻⁴ N, attractive
- D. 3.0 × 10⁻⁴ N, attractive
Q14. A flat coil of 100 turns and area 0.020 m² carries 0.50 A in a uniform field of 0.10 T. The normal to the coil makes 30° with the field. What is the torque on it?
- A. 0.10 N m
- B. 0.50 N m
- C. 0.05 N m
- D. 0.087 N m
Q15. A proton and an alpha particle are each accelerated from rest through the same potential difference and then enter the same uniform magnetic field at right angles to it. What is the ratio of the radii, r(α) : r(p)? (m_α = 4m_p, q_α = 2q_p)
- A. 2 : 1
- B. 1 : 1
- C. √2 : 1
- D. 1 : √2
Q16. The magnetic flux linked with a coil of 200 turns changes uniformly from 0.050 Wb to 0.010 Wb in 0.10 s. What is the magnitude of the induced EMF?
- A. 8.0 V
- B. 4.0 V
- C. 0.40 V
- D. 80 V
Q17. An inductor of 0.50 H carries a steady current of 2.0 A. How much energy is stored in its magnetic field?
- A. 1.0 J
- B. 4.0 J
- C. 2.0 J
- D. 0.5 J
Q18. A transformer steps 220 V down to 11 V and supplies 5.0 A to a load. If its efficiency is 90%, what current does the primary draw?
- A. 0.50 A
- B. 0.22 A
- C. 0.28 A
- D. 0.25 A
Q19. A series circuit has a resistance of 30 Ω, an inductive reactance of 80 Ω and a capacitive reactance of 40 Ω. What is its impedance?
- A. 70 Ω
- B. 110 Ω
- C. 50 Ω
- D. 90 Ω
Q20. A series LCR circuit has L = 1.0 mH and C = 10 nF. What is its resonant frequency?
- A. 5.03 kHz
- B. 50.3 kHz
- C. 159 kHz
- D. 31.6 kHz
Q21. 100 kW is transmitted through a line of resistance 5.0 Ω at 10 kV. What power is lost as heat in the line?
- A. 5000 W
- B. 50 W
- C. 500 kW
- D. 500 W
Q22. A 100 μF capacitor is charged through a 10 kΩ resistor from a 10 V battery. What is the voltage across the capacitor 2.0 s after charging begins?
- A. 8.65 V
- B. 10.0 V
- C. 6.32 V
- D. 7.50 V
Q23. Four equal charges of +1.0 nC are placed at the corners of a square of side 0.30 m. What are the electric potential and the electric field at the centre of the square? (k = 9.0 × 10⁹ N m² C⁻²)
- A. 0 V and 170 N C⁻¹
- B. 170 V and zero
- C. 170 V and 170 N C⁻¹
- D. 85 V and zero
Q24. An electron (e/m = 1.76 × 10¹¹ C kg⁻¹) is placed in a uniform electric field of 1000 N C⁻¹. What is the magnitude of its acceleration?
- A. 1.76 × 10¹⁴ m s⁻²
- B. 1.76 × 10¹¹ m s⁻²
- C. 1.76 × 10⁸ m s⁻²
- D. 9.8 m s⁻²
Q25. Dry air breaks down at an electric field of about 3.0 × 10⁶ V m⁻¹. What is the energy density of the field just before breakdown? (ε₀ = 8.85 × 10⁻¹² F m⁻¹)
- A. 13.3 J m⁻³
- B. 3.98 × 10⁻⁵ J m⁻³
- C. 39.8 J m⁻³
- D. 79.7 J m⁻³
Q26. Four identical cells, each of EMF 1.5 V and internal resistance 0.50 Ω, supply a 0.50 Ω load. Which statement about the current is correct?
- A. The series and parallel arrangements both give 2.4 A
- B. The series arrangement gives more current than the parallel one
- C. Both arrangements give 1.5 A
- D. The parallel arrangement gives more current than the series one
Q27. A circular coil of 50 turns and radius 10 cm carries a current of 2.0 A. What is its magnetic dipole moment?
- A. 0.063 A m²
- B. 3.14 A m²
- C. 10.0 A m²
- D. 31.4 A m²
Q28. A parallel-plate capacitor is charged and disconnected from the battery. The plates are then pulled apart until the separation is doubled. What happens to the stored energy?
- A. It quadruples
- B. It halves
- C. It stays the same
- D. It doubles
Q29. The centre of a circular coil of 50 turns and radius 10 cm, carrying 2.0 A, lies at the origin. What is the magnetic field there? (μ₀ = 4π × 10⁻⁷ T m A⁻¹)
- A. 6.28 × 10⁻⁴ T
- B. 6.28 × 10⁻⁶ T
- C. 12.6 × 10⁻⁴ T
- D. 3.14 × 10⁻⁴ T
Q30. The magnetic flux through a closed loop of total resistance 10 Ω changes by 0.020 Wb, taking any amount of time. What total charge flows through the loop?
- A. 20 mC
- B. 0.20 mC
- C. It depends on the time taken
- D. 2 mC