Magnetic Effects of Current and Magnetism – Class 12 Physics | WB HS Exam MCQs

Magnetic Effects of Current and Magnetism – Class 12 Physics

Magnetism and the effects of current play a crucial role in physics. It explains the fundamental principles behind electromagnets, solenoids, and the Earth's magnetic field. This topic is significant for students preparing for the West Bengal Higher Secondary (WB HS) Examination.

Key Concepts and Definitions

1. Magnetic Field (B): A region around a magnet where its influence is felt. Measured in Tesla (T).
2. Biot-Savart Law: Describes the magnetic field produced by a current element. $dB = \frac{\mu_0}{4\pi} \frac{Idl \sin\theta}{r^2}$
3. Ampere’s Circuital Law: States that $\oint B \cdot dl = \mu_0 I_{\text{enclosed}}$.
4. Lorentz Force: The force on a charged particle moving in a magnetic field: $F = q(E + v \times B)$.
5. Solenoid and Toroid: Long coil of wire producing a uniform magnetic field.
6. Cyclotron: A device used to accelerate charged particles using a perpendicular magnetic field.
7. Earth’s Magnetism: The Earth acts as a huge bar magnet with its magnetic field affecting compasses.

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Most Important MCQs for WB HS Exam

1. The SI unit of the magnetic field is:
   a) Weber
   b) Gauss
   c) Tesla
   d) Henry

2. The right-hand thumb rule is used to determine:
   a) Direction of magnetic force
   b) Direction of electric field
   c) Direction of current in a conductor
   d) Direction of induced current

3. The force on a charged particle moving perpendicular to a uniform magnetic field is:
   a) Maximum
   b) Minimum
   c) Zero
   d) Infinite

4. A current-carrying solenoid behaves like:
   a) An electric dipole
   b) A bar magnet
   c) A charged particle
   d) A capacitor

5. Ampere’s Circuital Law is used to determine the magnetic field due to:
   a) Solenoids
   b) Straight current-carrying conductors
   c) Toroids
   d) All of the above

6. The torque on a magnetic dipole in a uniform magnetic field is given by:
   a) $\tau = m \times B$
   b) $\tau = qE$
   c) $\tau = mv^2/r$
   d) $\tau = IB$

7. The working principle of a moving coil galvanometer is based on:
   a) Ohm’s Law
   b) Ampere’s Law
   c) Magnetic Torque
   d) Faraday’s Law

8. The magnetic field inside a toroid is:
   a) Zero
   b) Infinite
   c) Constant
   d) Variable

9. The unit of permeability of free space (μ₀) is:
   a) H/m
   b) Tm/A
   c) Wb/m²
   d) A/m

10. Cyclotron is used for accelerating:
    a) Neutral particles
    b) Charged particles
    c) Photons
    d) Neutrons

11. Magnetic field at the center of a circular current-carrying coil is:
    a) Zero
    b) Maximum
    c) Minimum
    d) Infinite

12. The direction of the magnetic field around a straight current-carrying conductor is given by:
    a) Fleming’s Left Hand Rule
    b) Right-Hand Thumb Rule
    c) Lenz’s Law
    d) Fleming’s Right Hand Rule

13. A moving charged particle produces:
    a) Only electric field
    b) Only magnetic field
    c) Both electric and magnetic fields
    d) No field

14. Which device works on the principle of force on a current-carrying conductor in a magnetic field?
    a) Transformer
    b) AC Generator
    c) Electric Motor
    d) Inductor

15. When a conductor moves perpendicular to a magnetic field, the induced EMF is given by:
    a) $E = Bvl$
    b) $E = Bvl \sin\theta$
    c) $E = Bv^2l$
    d) $E = \frac{Bvl}{\sin\theta}$

16. A current-carrying wire produces a magnetic field due to:
    a) Electric force
    b) Coulomb’s Law
    c) Moving charges
    d) Gravitational force

17. The SI unit of the magnetic dipole moment is:
    a) Am²
    b) Tm²
    c) Nm²
    d) Wb/m

18. The force between two parallel current-carrying conductors is:
    a) Inversely proportional to their length
    b) Directly proportional to the product of currents
    c) Independent of the distance between them
    d) Always repulsive

19. A moving coil galvanometer is converted into an ammeter by:
    a) Connecting a high resistance in series
    b) Connecting a high resistance in parallel
    c) Connecting a low resistance in series
    d) Connecting a low resistance in parallel

20. The SI unit of magnetic flux is:
    a) Weber (Wb)
    b) Tesla (T)
    c) Ampere (A)
    d) Henry (H)

21. The frequency of revolution of a charged particle in a uniform magnetic field depends on:
    a) Charge and mass of the particle
    b) Velocity of the particle
    c) Magnetic field strength
    d) Both a and c

22. What is the relation between magnetic field strength and distance in a long straight current-carrying wire?
    a) $B \propto \frac{1}{r}$
    b) $B \propto r$
    c) $B \propto r^2$
    d) $B \propto \frac{1}{r^2}$

23. In which case will a charged particle move in a circular path?
    a) When it moves parallel to the magnetic field
    b) When it moves perpendicular to the magnetic field
    c) When it is at rest in the field
    d) When the field is weak

24. What is the work done by a magnetic force on a moving charge?
    a) Maximum
    b) Zero
    c) Depends on the velocity
    d) Infinite

25. A soft iron core is used inside a solenoid to:
    a) Increase magnetic field strength
    b) Decrease the magnetic field
    c) Prevent heating
    d) Reduce resistance

26. A charged particle moves undeflected in a certain region of space. What can be concluded?
    a) Only electric field is present
    b) Only magnetic field is present
    c) Both electric and magnetic fields are present and balanced
    d) No field is present

27. If a charge moves parallel to a magnetic field, the force on it is:
    a) Maximum
    b) Zero
    c) Equal to its weight
    d) Perpendicular to its motion

28. The torque on a current loop in a uniform magnetic field is given by:
    a) $\tau = nIBA \cos\theta$
    b) $\tau = nIBA \sin\theta$
    c) $\tau = nBIA^2$
    d) $\tau = BIA^2$

29. The permeability of free space ($\mu_0$) is numerically equal to:
    a) $4\pi \times 10^{-7}$ Tm/A
    b) $3.14 \times 10^{-6}$ Tm/A
    c) $2\pi \times 10^{-7}$ Tm/A
    d) $4\pi \times 10^{-6}$ Tm/A

30. The strength of the Earth's magnetic field is approximately:
    a) $10^2$ T
    b) $10^{-1}$ T
    c) $10^{-4}$ T
    d) $10^{-10}$ T

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These 30+ MCQs cover key concepts for the West Bengal HS Exam.

Answers are here : 

1. (c) Tesla
2. (b) Right-Hand Thumb Rule
3. (c) Both electric and magnetic fields
4. (c) Electric Motor
5. (a) $E = Bvl$
6. (c) Moving charges
7. (a) Am²
8. (b) Directly proportional to the product of currents
9. (d) Connecting a low resistance in parallel
10. (a) Weber (Wb)
11. (b) Maximum
12. (b) Right-Hand Thumb Rule
13. (c) Both electric and magnetic fields
14. (c) Electric Motor
15. (a) $E = Bvl$
16. (c) Moving charges
17. (a) Am²
18. (b) Directly proportional to the product of currents
19. (d) Connecting a low resistance in parallel
20. (a) Weber (Wb)
21. (d) Both a and c
22. (a) $B \propto \frac{1}{r}$
23. (b) When it moves perpendicular to the magnetic field
24. (b) Zero
25. (a) Increase magnetic field strength
26. (c) Both electric and magnetic fields are present and balanced
27. (b) Zero
28. (b) $\tau = nIBA \sin\theta$
29. (a) $4\pi \times 10^{-7}$ Tm/A
30. (c) $10^{-4}$ T

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Conclusion

Understanding the Magnetic Effects of Current and Magnetism is essential for WB HS students. Practicing MCQs and key concepts will help in scoring high marks in the Physics exam. Stay tuned to MightyKnowledge for more exam-focused content.

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