Tag: making magnets

Questions Related to making magnets

State whether true or false :
Magnetization by electric current method creates more powerful magnets than other  methods of magnetization.

physics properties of a magnetic field let's make a magnet making magnets making and handling magnets

  1. True

  2. False

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Correct Option: A
Explanation:

Magnetization. There are a variety of methods that can be used to establish a magnetic field in a component for evaluation using magnetic particle inspection. It is common to classify the magnetizing methods as either direct or indirect. With direct magnetization, current is passed directly through the component.Rubbing the nail with the permanent magnet causes a stronger, more lasting magnetism in the nail. For this to work, only one pole of the magnet must stroke the nail from one end to the other in a single direction. ... It usually takes around 20 to 30 strokes before the nail becomes sufficiently magnetized.

For a permanent magnet, properties of material should be

physics properties of a magnetic field let's make a magnet making magnets making and handling magnets

  1. high retentivity high coercivity

  2. low retentivity law coercivity

  3. high retentivity low coercivity

  4. low retentivity high coercivity

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Correct Option: A

A rod of cross-sectional area $10$ $cm^2$ is placed with its length parallel to a magnetic field of intensity $1000$ ${A/m}$ , the flux through the rod is $10^4$ $webers$. Then the permeability of material of the rod is:

physics properties of a magnetic field let's make a magnet making magnets making and handling magnets

  1. $10^4$ ${wb/Am}$

  2. $10^3$ ${wb/Am}$

  3. $10^2$ ${wb/Am}$

  4. $10$ ${wb/Am}$

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Correct Option: A
Explanation:
Magnetic field of intensity $(H)=1000\ A/m$
$Flux$ through rod $(\phi)=10^4 \ Wb$
Area of mass section $(A)=10\ cm^2 =10\times 10^{-4}m^2$
$\Rightarrow \ A=10^{-3}m^2$

we know,
$\boxed {B=\dfrac {\phi}{A}= \mu H}$           (where $B$ is magnetic flux density)
  $\Rightarrow \ \dfrac {10^4}{10^{-3}}= \mu (1000)$
$\ \Rightarrow \ \mu =\dfrac {10^4}{10^{-3} \times 1000}=10^4\ Wb /Am$

hence $\boxed {\mu =10^4 \ Wb/Am}$,

so $(A)$ option is correct

permeability of material of rod

A domain in a ferromagnetic substance is in form of a cube of side length $1 \,\mu m$. It is contains $8 \times 10^{10}$ atoms and each atomic dipole has a moment of $9 \times 10^{-24} A \,m^2$, then the magnetization of the domain is then

physics properties of a magnetic field let's make a magnet making magnets making and handling magnets

  1. $7.2 \times 10^5 \,A \,m^{-1}$

  2. $7.2 \times 10^3 \,A \,m^{-1}$

  3. $7.2 \times 10^9 \,A \,m^{-1}$

  4. $7.2 \times 10^{12} \,A \,m^{-1}$

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Correct Option: A
Explanation:

Magnitisation $= \dfrac{M}{v}$

$= \dfrac{8 \times 10^{10} \times 9 \times 10^{-24}}{(10 - 6)^3}$

$= 7.2 \times 10^5 \,Am^{-1}$

The magnetic force required to demagnetize the material is called:

physics properties of a magnetic field let's make a magnet making magnets making and handling magnets

  1. Retentivity

  2. Coercivity

  3. Energy loss

  4. Hysteresis

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Correct Option: B
Explanation:

The coercivity of a substance is a measure of the reverse magnetising field required to destroy the residual magnetism of the substance.

A permanent magnet in the shape of a thin cylinder of length $10$cm has magnetisation $(M) = 10^6 A m^{-1}$. It's magnetization current $I _M$ will be then

physics properties of a magnetic field let's make a magnet making magnets making and handling magnets

  1. $10^5$A

  2. $10^6$A

  3. $10^7$A

  4. $10^8$A

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Correct Option: A
Explanation:

Given,

$M=10^6 A/m$
$l=10cm=0.1m$
Magnetization, $M=\dfrac{I _M}{l}$ 
$I _M=Ml=10^6\times 0.1$
$I _M=10^5A$
The correct option is A.