Doubling the radius of a circular coil halves the magnetic field at its centre, and Fleming's left hand rule gives the direction of force on a conductor, so this Class 12 sheet opens with the coil field and its direction rule. The tesla is the field unit in the key.
Key Takeaways
Doubling coil radius halves the field at its centre (Q1).
Fleming's left hand rule gives the force direction (Q2).
Q4 records tesla as the field unit.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.The magnetic field at the centre of a circular coil is B = μ₀I/2R. If the radius of the coil is doubled keeping the current the same, the field becomes:
(a) double(b) half(c) four times(d) unchanged
2.The direction of the force on a current-carrying conductor placed in a magnetic field is given by:
(a) Fleming's left hand rule(b) Fleming's right hand rule(c) the right hand thumb rule(d) Lenz's law
3.A charge moving parallel to a uniform magnetic field experiences:
(a) zero force(b) maximum force(c) a force equal to qvB(d) a force that changes its speed
4.The SI unit of magnetic field is the:
(a) tesla(b) weber(c) gauss(d) henry
5.According to the Biot-Savart law, the magnetic field due to a current element is proportional to:
(a) dL/r(b) dL sinθ/r²(c) dL/r²(d) r²/dL
6.The radius of the circular path of a charge moving perpendicular to a magnetic field is:
(a) qB/mv(b) mq/vB(c) mv/qB(d) vB/mq
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.State the Biot-Savart law and write its vector expression.
8.Write the expression for the force on a straight current-carrying conductor placed in a uniform magnetic field. When is this force maximum?
9.Define the SI unit ampere in terms of the force between two long parallel current-carrying conductors.
10.State and explain Fleming's left hand rule.
11.What is the Lorentz force? Write its expression.
12.Write the expression for the magnetic field at the centre of a circular current-carrying loop of N turns and radius R.
13.Under what condition is the magnetic force on a moving charge zero?
14.What is the nature of the path followed by a charged particle entering a uniform magnetic field (a) perpendicular to the field, (b) at an acute angle to the field?
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A long straight wire carries a current of 10 A. Using B = μ₀I/2πr with μ₀ = 4π × 10⁻⁷ T·m/A, find the magnetic field at a point 0.05 m from the wire.
16.A circular coil of 100 turns and radius 0.1 m carries a current of 2 A. Using B = μ₀NI/2R with μ₀ = 4π × 10⁻⁷ T·m/A, find the magnetic field at its centre.
17.An electron moves with a speed of 10⁶ m/s perpendicular to a magnetic field of 0.1 T. Using F = evB with e = 1.6 × 10⁻¹⁹ C, find the magnitude of the force on the electron.
18.A proton enters a uniform magnetic field of 1 T perpendicular to it with a speed of 10⁷ m/s. Using r = mv/qB with m = 1.67 × 10⁻²⁷ kg and e = 1.6 × 10⁻¹⁹ C, find the radius of its circular path.
19.Two long parallel wires carry currents of 5 A each in the same direction and are 0.1 m apart. Using F/L = μ₀I₁I₂/2πd with μ₀ = 4π × 10⁻⁷ T·m/A, find the force per unit length between them and state whether it is attractive or repulsive.
20.A straight wire of length 0.5 m carrying a current of 4 A is placed perpendicular to a magnetic field of 0.3 T. Using F = BIL, find the force on the wire.
Answer Key
1. b) half
2. a) Fleming's left hand rule
3. a) zero force
4. a) tesla
5. b) dL sinθ/r²
6. c) mv/qB
7. Refer to solution guide.
8. Refer to solution guide.
9. Refer to solution guide.
10. Refer to solution guide.
11. Refer to solution guide.
12. Refer to solution guide.
13. Refer to solution guide.
14. Refer to solution guide.
15. Refer to solution guide.
16. Refer to solution guide.
17. Refer to solution guide.
18. Refer to solution guide.
19. Refer to solution guide.
20. Refer to solution guide.
End of Worksheet
People Also Ask
What happens to the field when a coil's radius doubles?
It becomes half, option (b) in this worksheet (Q1).
Which rule gives the force direction on a conductor in a field?
Fleming's left hand rule, option (a) in this worksheet (Q2).
What is the unit of magnetic field?
The tesla, option (a) in this worksheet (Q4).
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