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Multiple choice physics magnetism and matter paramagnetic material classification of magnetic material magnetism

The purpose of soft iron cylinder between the pole pieces of the horse-shoe magnet in a moving coil galvanometer is 

  1. to increase the magnetic induction in the polar

    gap

  2. to evenly distribute the magnetic lines of force

  3. to provide a radial magnetic field

  4. to reduce the magnetic flux leakage in the polar

    gap
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Soft iron cylinder is placed between the pole pieces of the horse-shoe magnet in a moving coil galvanometer to increase the magnetic induction in the polar gap. Soft iron is paramagnetic which increases magnetic induction when placed in field because atoms in soft iron align in such manner that it increases field.

Multiple choice physics magnetism and matter paramagnetic material classification of magnetic material magnetism

A bar magnet has been cut equally lengthwise and widthwise to give four equal pieces. The pole strength of each piece as compared to the pole strength of original bar magnet is :

  1. Same

  2. $\displaystyle \frac{1}{8}$

  3. $\displaystyle \frac{1}{4}$

  4. $\displaystyle \frac{1}{2}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When a bar magnet is cut equally lengthwise and widthwise into four equal pieces, each piece has 1/4 the length and 1/2 the width of the original. Pole strength is proportional to cross-sectional area (width × thickness). Original area A = w × t. Each piece has area = (w/2) × t = A/2. Therefore pole strength of each piece is half the original pole strength.

Multiple choice physics magnetism and matter paramagnetic material classification of magnetic material magnetism

Magnetic permeability of paramagnetic substances is?

  1. $0$

  2. $> 1$

  3. $< 1$

  4. $1$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Paramagnetic substances are substances which are weakly attracted by the magnetic field when they are placed in an external magnetic field. Magnetic permeability of paramagnetic substances is slightly greater than one whereas that of diamagnetic materials is slightly less than one.

Multiple choice physics magnetism and matter paramagnetic material classification of magnetic material magnetism

How will you quantize the relative permeability of a paramagnetic substance ?

  1. Much more than one

  2. Slightly more than one

  3. Less than one but greater than zero

  4. Zero
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Paramagnetic substances are those which are attracted slightly in the direction of the magnetic field. As such, the magnetic permeability of these materials is slightly greater than $1$. 
Similarly, diamagnetic materials are those which are repelled slightly away from the direction of magnetic field. These materials have their permeability slightly less than $1$.
And ferromagnetic materials are those which are attracted very strongly and their permeabilities are much higher than $1$.

Multiple choice physics magnetism and matter paramagnetic material classification of magnetic material magnetism

The relative permeability is represented by $\mu _r$ and the susceptibility by $\chi$ for a magnetic substance. Then, for a paramagnetic substance. Then, for a paramagnetic substance 

  1. $\mu _r> 1, \chi >0$

  2. $\mu _r> 1, \chi < 0$

  3. $\mu _r > 1, \chi >0$

  4. $\mu _r < 1, \chi < 0$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Susceptence $(\chi) = \dfrac{B-B _0}{B _0}$


Where $B _0$ is external applied magnetic field and $B$ is magnetic field in presence of paramagnetic substance.
Since dipoles in paramagnetic substance align in direction of applied magnetic filed, therefore $B > B _0$

And $B$ is bit more than $B _0$
$\Rightarrow \chi > 0$

And also $\mu _r = \chi + 1$
$\Rightarrow \mu _r  > 0 + 1$
$ \Rightarrow \mu _r > 1$
Therefore option A is correct.