ECAT — Engineering College Admission Test (UET)

ECAT Physics — Magnetism, Electromagnetic Induction and AC (Set 3)

Take the ECAT Physics — Magnetism, Electromagnetic Induction and AC (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a full…

What this test covers

30 ECAT Physics

Sample questions with answers

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

Q1. A straight wire carries 10 A. The magnetic field at a perpendicular distance of 5 cm is (μ₀ = 4π × 10⁻⁷ T m/A)
- A. 8π × 10⁻⁵ T
- B. 4 × 10⁻⁵ T ✓
- C. 2 × 10⁻⁵ T
- D. 4 × 10⁻⁴ T
Answer: B. 4 × 10⁻⁵ T
Explanation: B = μ₀I/2πr = 2×10⁻⁷ × 10/0.05 = 4e-05 T.
Q2. Two long parallel wires carry currents in the same direction. They
- A. exert no force on each other
- B. rotate about each other
- C. attract each other ✓
- D. repel each other
Answer: C. attract each other
Explanation: Parallel currents in the same direction attract; opposite currents repel.
Q3. The force per metre between two long parallel wires 10 cm apart, each carrying 10 A, is
- A. 2 × 10⁻⁶ N/m
- B. 4π × 10⁻⁴ N/m
- C. 2 × 10⁻² N/m
- D. 2 × 10⁻⁴ N/m ✓
Answer: D. 2 × 10⁻⁴ N/m
Explanation: F/L = μ₀I₁I₂/2πd = 2×10⁻⁷ × 100/0.1 = 2e-04 N/m.
Q4. A solenoid has 500 turns on a length of 0.25 m and carries 2 A. The magnetic field inside it is
- A. 1.6π × 10⁻³ T ✓
- B. 3.2π × 10⁻³ T
- C. 1.6π × 10⁻⁵ T
- D. 0.8π × 10⁻³ T
Answer: A. 1.6π × 10⁻³ T
Explanation: n = 500/0.25 = 2000 per m; B = μ₀nI = 4π×10⁻⁷ × 2000 × 2 = 1.6π × 10⁻³ T.
Q5. A proton moves at 2 × 10⁶ m/s perpendicular to a magnetic field of 0.5 T. The force on it is
- A. 3.2 × 10⁻¹³ N
- B. 1.6 × 10⁻¹⁶ N
- C. 8 × 10⁻¹⁴ N
- D. 1.6 × 10⁻¹³ N ✓
Answer: D. 1.6 × 10⁻¹³ N
Explanation: F = qvB = 1.6×10⁻¹⁹ × 2×10⁶ × 0.5 = 1.6e-13 N.

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. The proton above (m = 1.67 × 10⁻²⁷ kg) moves in a circle of radius approximately
- A. 42 cm
- B. 4.2 cm
- C. 8.4 cm
- D. 2.1 cm
Q7. A charged particle enters a uniform magnetic field parallel to the field lines. It will
- A. move in a circle
- B. move in a straight line at constant speed
- C. be brought to rest
- D. move in a helix
Q8. A velocity selector has E = 2 × 10⁴ V/m and B = 0.1 T crossed. The speed of undeflected particles is
- A. 2 × 10⁷ m/s
- B. 5 × 10⁻⁶ m/s
- C. 2 × 10³ m/s
- D. 2 × 10⁵ m/s
Q9. A square coil of side 10 cm has 50 turns and carries 4 A. It hangs in a 0.25 T field with its plane parallel to the field. The torque on it is
- A. 1 N m
- B. 0.25 N m
- C. 0.5 N m
- D. 0.05 N m
Q10. A galvanometer of resistance 50 Ω gives full-scale deflection for 2 mA. To make an ammeter reading 1 A, the shunt resistance required is approximately
- A. 0.5 Ω
- B. 0.1 Ω
- C. 25 Ω
- D. 50 Ω
Q11. The same galvanometer (50 Ω, 2 mA full scale) is to be converted into a voltmeter reading 10 V. The series resistance required is
- A. 4950 Ω
- B. 50 Ω
- C. 4900 Ω
- D. 5000 Ω
Q12. A rod 0.5 m long moves at 4 m/s perpendicular to a magnetic field of 0.2 T. The emf induced between its ends is
- A. 0.1 V
- B. 0.4 V
- C. 4 V
- D. 0.8 V
Q13. A coil of 200 turns experiences a flux change from 0.01 Wb to 0.05 Wb in 0.4 s. The average induced emf is
- A. 8 V
- B. 2 V
- C. 80 V
- D. 20 V
Q14. A magnet is pushed north-pole first towards a coil. The induced current in the coil flows in the direction that
- A. produces a south pole on that face
- B. is independent of the magnet’s motion
- C. produces a north pole on the coil face nearest the magnet
- D. helps the magnet to approach
Q15. A coil has self-inductance 0.5 H. The emf induced when the current changes at 8 A/s is
- A. 0.0625 V
- B. 4 V
- C. 8.5 V
- D. 16 V
Q16. The energy stored in a 0.5 H inductor carrying 4 A is
- A. 8 J
- B. 4 J
- C. 2 J
- D. 1 J
Q17. A transformer has 100 primary turns and 2500 secondary turns, with 220 V applied to the primary. The secondary voltage is
- A. 5500 V
- B. 2200 V
- C. 550 V
- D. 8.8 V
Q18. An ideal step-down transformer reduces 2200 V to 220 V and the secondary supplies 50 A. The primary current is
- A. 5 A
- B. 0.5 A
- C. 50 A
- D. 500 A
Q19. The rms value of an alternating current whose peak value is 10 A is
- A. 10 A
- B. 7.07 A
- C. 14.1 A
- D. 5 A
Q20. An AC source has V = 311 sin(100πt). The frequency and rms voltage are
- A. 50 Hz and 220 V
- B. 100 Hz and 311 V
- C. 100 Hz and 220 V
- D. 50 Hz and 311 V
Q21. An inductor of 0.1 H is connected to a 50 Hz supply. Its reactance is approximately
- A. 5 Ω
- B. 3.14 Ω
- C. 314 Ω
- D. 31.4 Ω
Q22. A 100 μF capacitor is used on a 50 Hz supply. Its reactance is approximately
- A. 318 Ω
- B. 0.03 Ω
- C. 3.18 Ω
- D. 31.8 Ω
Q23. A series circuit has R = 30 Ω and net reactance 40 Ω. The impedance is
- A. 10 Ω
- B. 50 Ω
- C. 70 Ω
- D. 1200 Ω
Q24. A series LCR circuit has L = 0.1 H and C = 100 μF. Its resonant frequency is approximately
- A. 159 Hz
- B. 503 Hz
- C. 50.3 Hz
- D. 5.03 Hz
Q25. In a purely inductive AC circuit, the phase relation between voltage and current is that the voltage
- A. lags the current by 90°
- B. leads the current by 90°
- C. is opposite in phase to the current
- D. is in phase with the current
Q26. A circuit draws 5 A rms from a 220 V supply at a power factor of 0.6. The average power consumed is
- A. 396 W
- B. 1833 W
- C. 660 W
- D. 1100 W
Q27. A choke coil is preferred to a resistor for controlling AC in a lamp circuit because
- A. it limits the current with almost no power loss
- B. it converts the AC supply to DC for the lamp
- C. it has a much higher resistance than any resistor
- D. it raises the supply voltage across the lamp
Q28. A coil rotating in a uniform magnetic field generates the maximum emf when
- A. its plane is parallel to the field
- B. the flux through it is maximum
- C. its plane is perpendicular to the field
- D. its axis is along the field
Q29. A motor with armature resistance 2 Ω runs on 120 V and draws 10 A. The back emf is
- A. 20 V
- B. 120 V
- C. 140 V
- D. 100 V
Q30. The magnetic flux through a loop of area 0.04 m² in a uniform field of 0.5 T at 60° between the field and the loop’s normal is
- A. 0.02 Wb
- B. 0.017 Wb
- C. 0.01 Wb
- D. 0.04 Wb