JEE Main Magnetism and Matter PYQ

11. (JEE Main 2020 (Online) 3rd September Evening Slot)

A perfectly diamagnetic sphere has a small spherical cavity at its centre, which is filled with a paramagnetic substance. The whole system is placed in a uniform magnetic field $\vec{B}$ . Then the field inside the paramagnetic substance is : JEE Main 2020 (Online) 3rd September Evening Slot Physics - Magnetic Properties of Matter Question 40 English

A. $\vec{B}$

B. zero

C. much large than $| \vec{B} |$ and parallel to $\vec{B}$

D. much large than $| \vec{B} |$ but opposite to $\vec{B}$

Correct Option is (B)

A perfect diamagnetic substance will completely expel the magnetic field. Therefore, there will be no magnetic field inside the cavity of sphere. Hence the paramagnetic substance kept inside the cavity will experience no force.

12. (JEE Main 2020 (Online) 2nd September Morning Slot)

Magnetic materials used for making permanent magnets (P) and magnets in a transformer (T) have different properties of the following, which property best matches for the type of magnet required?

A. T : Large retentivity, small coercivity

B. P : Large retentivity, large coercivity

C. p : Small retentivity, large coercivity

D. T : Large retentivity, large coercivity

Correct option is (B)

Option (B) is correct as permanent magnet should have high coercivity & retentivity.

13. (JEE Main 2020 (Online) 7th January Evening Slot)

JEE Main 2020 (Online) 7th January Evening Slot Physics - Magnetic Properties of Matter Question 43 English The figure gives experimentally measured B vs H variation in a ferromagnetic material. The retentivity, coercivity and saturation, respectively, of the material are :

A. 1.0 T, 50 A/m and 1.5 T

B. 1.5 T, 50 A/m and 1.0 T

C. 1.5 T, 50 A/m and 2.0 T

D. 150 A/m, 1.0 T and 1.5 T

Correct option is (A)

JEE Main 2020 (Online) 7th January Evening Slot Physics - Magnetic Properties of Matter Question 43 English Explanation
Retentivity = 1.0 T

Co-ercivity = 50 A/m

Saturation = 1.5 T

14. (JEE Main 2018 (Online) 15th April Morning Slot)

The $B$ - $H$ curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solended with $1000$ turns/cm. The current that should be passed in the solended to demagnetise the ferromagnet completely is :

JEE Main 2018 (Online) 15th April Morning Slot Physics - Magnetic Properties of Matter Question 52 English

A. $1$ $m A$

B. $2$ $m A$

C. $20 μ A$

D. $40 μ A$

Correct option is (A)

Given that,

In the solenoid there is 1000 turns in 1 cm.

$∴$ In 100 cm or 1 m no of turns

= 1000 $\times$ 100 = 10⁵ turns/m

$∴$ No of turns, n = 10⁵

Correctivity of ferromagnet, H = 100 A/m

As we know,

H = n I

$∴$ I = $\frac{100}{10^{5}} = 1 m A$

$∴$ Current to demagnetise the ferromagnet = 1 mA.

15. (JEE Main 2016 (Offline))

Hysteresis loops for two magnetic materials $A$ and $B$ are given below : JEE Main 2016 (Offline) Physics - Magnetic Properties of Matter Question 54 English

These materials are used to make magnets for electric generators, transformer core and electromagnet core. Then it is proper to use :

A. A for transformers and B for electric generators.

B. B for electromagnets and transformers.

C. A for electric generators and transformers.

D. A for the electromagnets and B for electric generators.

Correct option is (B)

Graph [A] is for material used for making permanent magnets (high coercivity) Graph [B] is for making electromagnets and transformers.