NEET Magnetism and Matter — Set 18

Question 1

A bar magnet with magnetic moment $ 1.5 \, \text{A m}^2 $ is placed at a distance of $ 0.6 \, \text{m} $ along its axis. What is the magnetic field $ B $ at that point? (Take $ \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} $).

Accepted Answer

The magnetic field along the axis is $ B = \frac{\mu_0}{4\pi} \frac{2m}{r^3} $. Given: $ m = 1.5 \, \text{A m}^2 $, $ r = 0.6 \, \text{m} $, $ \frac{\mu_0}{4\pi} = 10^{-7} $. Substitute: $ B = 10^{-7} \times \frac{2 \times 1.5}{(0.6)^3} = 10^{-7} \times \frac{3.0}{0.216} \approx 1.389 \times 10^{-6} \, \text{T} \approx 1.39 × 10^{-6} \, \text{T} $.

Question 2

A dipole with $ m = 0.5 \, \text{A m}^2 $ in $ B = 0.1 \, \text{T} $ at $ 60^\circ $ has torque:

Accepted Answer

$ \tau = m B \sin\theta $. Given: $ m = 0.5 \, \text{A m}^2 $, $ B = 0.1 \, \text{T} $, $ \theta = 60^\circ $, $ \sin 60^\circ = \frac{\sqrt{3}}{2} \approx 0.866 $. $ \tau = 0.5 \times 0.1 \times 0.866 = 0.0433 \, \text{N m} \approx 0.043 \, \text{N m} $.

Question 3

The magnetic field contribution $ B_m $ due to a material with $ M = 3.2 \times 10^5 \, \text{A m}^{-1} $ is: (Take $ \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} $).

Accepted Answer

$ B_m = \mu_0 M $. Given: $ M = 3.2 \times 10^5 \, \text{A m}^{-1} $, $ \mu_0 = 4\pi \times 10^{-7} $. $ B_m = 4\pi \times 10^{-7} \times 3.2 \times 10^5 = 0.40192 \, \text{T} \approx 0.40 \, \text{T} $.

NEET Physics: Magnetism and Matter — Practice Set 18

Q1. A bar magnet with magnetic moment \( 1.5 \, \text{A m}^2 \) is placed at a distance of \( 0.6 \, \text{m} \) along its axis. What is the magnetic field \( B \) at that point? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q2. A dipole with \( m = 0.5 \, \text{A m}^2 \) in \( B = 0.1 \, \text{T} \) at \( 60^\circ \) has torque:

Q3. The magnetic field contribution \( B_m \) due to a material with \( M = 3.2 \times 10^5 \, \text{A m}^{-1} \) is: (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q4. The magnetic field contribution \( B_m \) due to a material with \( M = 2 \times 10^5 \, \text{A m}^{-1} \) is: (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q5. Unlike a bar magnet, an iron nail near a magnet experiences both a net force and a torque. This is primarily due to:

Q6. The reason a paramagnetic material’s magnetization increases with a stronger external field is:

Q7. A dipole with \( m = 0.4 \, \text{A m}^2 \) in a field \( B = 0.8 \, \text{T} \) at \( 0^\circ \) has potential energy:

Q8. A diamagnetic material has a susceptibility \( \chi = -2 \times 10^{-5} \). What is its magnetic permeability \( \mu \) in terms of \( \mu_0 \)?

Q9. A material with \( \mu_r = 350 \) and \( H = 400 \, \text{A m}^{-1} \) has \( B \): (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q10. A bar magnet with \( m = 1.6 \, \text{A m}^2 \) is at \( 0.8 \, \text{m} \) along its axis. What is \( B \)? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).