NEET Magnetism and Matter — Set 1

Question 1

A solenoid produces $ B = 1.2 \, \text{T} $ with a core of $ \mu_r = 400 $ and $ n = 2000 \, \text{m}^{-1} $. What is the current $ I $? (Take $ \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} $).

Accepted Answer

$ B = \mu_0 \mu_r n I $, so $ I = \frac{B}{\mu_0 \mu_r n} $. Given: $ B = 1.2 \, \text{T} $, $ \mu_r = 400 $, $ n = 2000 \, \text{m}^{-1} $, $ \mu_0 = 4\pi \times 10^{-7} $. $ I = \frac{1.2}{4\pi \times 10^{-7} \times 400 \times 2000} = \frac{1.2}{1.005 \times 10^{0}} \approx 1.19 \, \text{A} \approx 1.2 \, \text{A} $.

Question 2

A bar magnet produces a magnetic field of $ 2 \times 10^{-5} \, \text{T} $ at a point $ 0.1 \, \text{m} $ along its axis. What is its magnetic moment? (Take $ \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} $).

Accepted Answer

$ B = \frac{\mu_0}{4\pi} \frac{2m}{r^3} $, so $ m = \frac{B r^3}{\frac{\mu_0}{4\pi} \times 2} $. Given: $ B = 2 \times 10^{-5} \, \text{T} $, $ r = 0.1 \, \text{m} $, $ \frac{\mu_0}{4\pi} = 10^{-7} $. $ m = \frac{2 \times 10^{-5} \times (0.1)^3}{10^{-7} \times 2} = \frac{2 \times 10^{-5} \times 0.001}{2 \times 10^{-7}} = 0.05 \, \text{A m}^2 $.

Question 3

A bar magnet with $ m = 1.0 \, \text{A m}^2 $ produces a field at $ 0.25 \, \text{m} $ on its equatorial line. What is $ B $? (Take $ \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} $).

Accepted Answer

$ B = \frac{\mu_0}{4\pi} \frac{m}{r^3} $. Given: $ m = 1.0 \, \text{A m}^2 $, $ r = 0.25 \, \text{m} $, $ \frac{\mu_0}{4\pi} = 10^{-7} $. $ B = 10^{-7} \times \frac{1.0}{(0.25)^3} = 10^{-7} \times \frac{1.0}{0.015625} = 6.4 \times 10^{-6} \, \text{T} $.

NEET Physics: Magnetism and Matter — Practice Set 1

Q1. A solenoid produces \( B = 1.2 \, \text{T} \) with a core of \( \mu_r = 400 \) and \( n = 2000 \, \text{m}^{-1} \). What is the current \( I \)? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q2. A bar magnet produces a magnetic field of \( 2 \times 10^{-5} \, \text{T} \) at a point \( 0.1 \, \text{m} \) along its axis. What is its magnetic moment? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q3. A bar magnet with \( m = 1.0 \, \text{A m}^2 \) produces a field at \( 0.25 \, \text{m} \) on its equatorial line. What is \( B \)? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q4. The reason a soft ferromagnetic material loses its magnetism when the external field is removed is:

Q5. A material’s ability to retain strong magnetism after an external field is removed is a property of:

Q6. A dipole with \( m = 0.9 \, \text{A m}^2 \) in \( B = 0.5 \, \text{T} \) at \( 90^\circ \) has torque:

Q7. A bar magnet produces a field of \( 5 \times 10^{-6} \, \text{T} \) at \( 0.4 \, \text{m} \) on its equatorial line. What is its magnetic moment? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q8. A solenoid with 1100 turns per meter and current \( 1.5 \, \text{A} \) has a core with \( \mu_r = 200 \). What is \( B \) inside? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q9. A bar magnet with \( m = 0.6 \, \text{A m}^2 \) produces a field at \( 0.3 \, \text{m} \) on its equatorial line. What is \( B \)? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q10. A superconductor has a susceptibility \( \chi \) of:

Q11. A bar magnet produces a field of \( 6 \times 10^{-6} \, \text{T} \) at \( 0.3 \, \text{m} \) on its equatorial line. What is its magnetic moment? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q12. Which of the following materials has \( \chi \) negative and tends to move from stronger to weaker magnetic field regions?

Q13. A bar magnet produces a field of \( 3 \times 10^{-6} \, \text{T} \) at \( 0.3 \, \text{m} \) on its equatorial line. What is its magnetic moment? (Take \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m A}^{-1} \)).

Q14. Why do magnetic field lines never intersect, unlike some electric field lines in complex charge distributions?

Q15. Which material has a negative \( \chi \) and is weakly repelled by a magnetic field?