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CBSE · Class 12 · Physics

Moving Charges and Magnetism

Standard difficulty · 20 questions · 40 marks

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
A proton moves at 2 × 106 m/s at 150° to a magnetic field of 6 × 10−1 T. The force on it is: (e = 1.6 × 10−19 C)
  1. 9.6 × 10−15 N
  2. 1.92 × 10−13 N
  3. 0 N
  4. 9.6 × 10−14 N
2.
A circular coil of 74 turns and radius 16 cm carries 9 A. The field at its centre is: (μ0 = 4π × 10−7 T m/A)
  1. 4.1625π × 10−4 T
  2. 8.325π × 10−6 T
  3. 8.325π × 10−4 T
  4. 8.325 × 10−4 T
3.
The magnetic field 3 cm from a long straight wire carrying 20 A is: (μ0 = 4π × 10−7 T m/A)
  1. 1.33 × 10−6 T
  2. 6.67 × 10−5 T
  3. 1.33π × 10−4 T
  4. 1.33 × 10−4 T
4.
Particles X (charge 4e, mass m) and Y (charge 4e, mass 6m) enter the same magnetic field at the same speed, at right angles to it. The ratio of the radii of their paths, r_X : r_Y, is:
  1. 1 : 6
  2. 1 : 1
  3. 2 : 6
  4. 6 : 1
5.
The SI unit of magnetic field is the:
  1. tesla
  2. gauss
  3. weber
  4. henry
6.
Two long parallel wires 11 cm apart carry 17 A and 3 A in the same direction. The force on each metre of wire is: (μ0 = 4π × 10−7 T m/A)
  1. 9.27 × 10−5 N, attractive
  2. 4.64 × 10−5 N, attractive
  3. 9.27 × 10−5 N, repulsive
  4. 9.27 × 10−7 N, attractive
7.
A long solenoid has 1000 turns per metre and carries 10 A. The field inside it is: (μ0 = 4π × 10−7 T m/A)
  1. 4π × 10−1 T
  2. 2π × 10−3 T
  3. 4π × 10−3 T
  4. 4 × 10−3 T
8.
Assertion (A): A proton moving at 6 × 106 m/s at right angles to a 8 × 10−1 T magnetic field speeds up steadily.
Reason (R): The magnetic force on a moving charge is perpendicular to its velocity, so it does no work.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
Section B — Short answer8 × 2 = 16 marks
9.
A circular coil of radius 19 cm has 12 turns and carries 7 A. Find the field at its centre. (μ0 = 4π × 10−7 T m/A)
10.
A wire 8 cm long carrying 16 A lies at 90° to a uniform field of 9 × 10−1 T. Find the force on it.
11.
A coil of 139 turns and area 32 cm2 carries 5 A in a field of 7 × 10−1 T. Find the torque on it when its plane makes 0° with the field (normal at 90°).
12.
A galvanometer of resistance 70 Ω gives full-scale deflection for 10 mA. What shunt converts it into an ammeter reading up to 8 A?
13.
A galvanometer of resistance 85 Ω gives full-scale deflection for 9 mA. What resistance in series converts it into a voltmeter reading up to 20 V?
14.
Two long parallel wires 5 cm apart carry 19 A and 8 A in opposite directions. Find the force per metre between them, and say whether they attract or repel. (μ0 = 4π × 10−7 T m/A)
15.
A particle of mass 9 × 10−26 kg and charge 3e moves at 2 × 105 m/s at right angles to a field of 7 × 10−1 T. Find the radius of its path. (e = 1.6 × 10−19 C)
16.
A toroid has 1600 turns and carries 3 A. Find the field inside its core at a radius of 20 cm. (μ0 = 4π × 10−7 T m/A)
Section C — Word problems4 × 4 = 16 marks
17.
A galvanometer has resistance 40 Ω and full-scale current 2 mA. Show how to convert it into (a) an ammeter of range 0–8 A, (b) a voltmeter of range 0–440 V, and find the resistance of each meter.
18.
A particle of mass 8 × 10−26 kg and charge 3e enters a field of 5 × 10−1 T at right angles with speed 9 × 105 m/s. Find the radius of its path, the time for one revolution, and its frequency. Does the time depend on the speed? (e = 1.6 × 10−19 C)
19.
Two long parallel wires 10 cm apart carry 18 A and 13 A in opposite directions. Find the magnetic field midway between them and the force on each metre of either wire. (μ0 = 4π × 10−7 T m/A)
20.
A rectangular coil of 175 turns, area 45 cm2, carries 5 A in a uniform field of 8 × 10−1 T. Find its magnetic moment, the largest torque on it, and the torque when its normal makes 30° with the field.
AmbifulWorksheets
Practice that never repeats
CBSE · Class 12 · Physics

Answer key

Moving Charges and Magnetism · AW-12P-MCM-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(d) 9.6 × 10−14 NF = qvB sin θ = 1.6 × 10−19 × 2 × 106 × 6 × 10−1 × sin 150°
2(c) 8.325π × 10−4 TB = μ0NI/(2R)
3(d) 1.33 × 10−4 TB = μ0I/(2πr) = 2 × 10−7 I/r
4(a) 1 : 6r = mv/(qB) ∝ m/q
5(a) tesla—
6(a) 9.27 × 10−5 N, attractiveF/L = μ0I1I2/(2πd)
7(c) 4π × 10−3 TB = μ0nI
8(d) A is false, but R is true.A is false: the magnetic force does no work, so the speed cannot change. R is true.
98.84π × 10−5 TB = μ0NI/(2R) = 4π × 10−7 × 12 × 7 ÷ (2 × 19 × 10−2)
101.152 NF = BIL sin θ = 9 × 10−1 × 16 × 8 × 10−2 × sin 90°
111.5568 N mτ = NIAB sin θ
120.0876 Ω in parallelS = I_g G/(I − I_g) = 10 × 10−3 × 70 ÷ (8 − 10 × 10−3)
132,137.22 ΩR = V/I_g − G
146.08 × 10−4 N/m; they repelF/L = 2 × 10−7 I1I2/d
150.0536 mr = mv/(qB) = 9 × 10−26 × 2 × 105 ÷ (3 × 1.6 × 10−19 × 7 × 10−1)
164.8 × 10−3 TB = μ0NI/(2πr) = 2 × 10−7 × 1600 × 3 ÷ (20 × 10−2)
17(a) shunt 0.01 Ω in parallel; ammeter resistance 0.01 Ω; (b) 219,960 Ω in series; voltmeter resistance 220,000 ΩS = I_gG/(I − I_g); R = V/I_g − G
18r = 0.3 m; T = 6.67π × 10−7 s; f = 1/T; no, T = 2πm/(qB) does not depend on vr = mv/(qB); T = 2πr/v
191.24 × 10−4 T; 4.68 × 10−4 N/m, repulsiveeach wire gives 2 × 10−7 I/(5 × 10−2) at the midpoint; they add
20m = 3.9375 A m2; τmax = 3.15 N m; τ = 1.575 N mm = NIA; τ = mB sin θ