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Std 12 PHYSICS > Magnetism > Flashcards

Magnetism Flashcards

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0
Q

Expression for magnetic induction at a a point in the axis at a distance x from the centre of a circular coil of radius a, carrying current i

A

B= μ0ia*a/(2(a^2 + x^2)^(3/2))

= (μ0/4π)*(2M/(x^3))

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1
Q

Properties of magnets

A

Directive property
Attractive property
Earth behaves as a magnet with magnetic field pointing approximately from geographical south to geographical north.
Magnetic monopoles do not exist.
Magnetism has its origin in circulating charges within the atoms of any substance.

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2
Q

Expression for magnetic dipole moment

A

M=IA

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3
Q

Magnetic dipole moment of a revolving electron - Derivation

A 
T= 2πr/v 
i= e/T
M= evr/2
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4
Q

What is the direction of magnetic moment of a rotating electron?

A

Into the plane of paper

Negative charged electrons move in anti-clockwise direction leading to clockwise current.

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5
Q

Relation between orbital angular momentum and orbital magnetic moment of an electron

A

__ __
M = -(e/2m)*L
In opposite directions

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6
Q

Define Gyromagnetic ratio

A

The ratio of magnetic dipole moment with angular momentum of revolving electron is called Gyromagnetic ratio.

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7
Q

Expression for Gyromagnetic ratio

A

M/L = e/2m

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8
Q

Value of Gyromagnetic ratio

A

8.8 * 10^8 C/kg

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9
Q

Define magnetization

A

The net magnetic dipole moment per unit volume of the sample is called as the magnetization of the sample.

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10
Q

Expression for magnetization

A

___ ___

Mz= Mnet/Volume

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11
Q

What is the unit of magnetization?

A

A/m

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12
Q

Is magnetization a scalar or vector quantity?

A

Vector

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13
Q

Dimensions of magnetization

A

[L-1 M0 T0 I1]

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14
Q

Define saturation of the sample

A

Complete alignment of the atomic dipole moment is called saturation of the sample.

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15
Q

State Curie law

A

Curie law states that, magnetization of a paramagnetic sample s directly proportional to the external magnetic field and inversely proportional to the absolute temperature.

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16
Q

What is the equation for Curie law?

A

Mz= C*Bext /T

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17
Q

What is magnetic intensity?

A

The vector quantity in terms of which strength of the magnetic field at a point can be given is known as magnetic intensity.

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18
Q

Relation between magnetic field and magnetic intensity

A

Bo=μο*Η

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19
Q

Unit of H

A

A/m

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20
Q

Dimensions of H

A

[L-1 M0 T0 I1]

21
Q

Relation between magnetization and magnetic intensity

A

Mz= χH

22
Q

Dimensions of susceptibility

A

Unitless, dimensionless

23
Q

χ for paramagnetic materials

A

Small and positive

24
Q

χ for diamagnetic materials

A

Small and negative

25
Q

χ for ferromagnetic materials

A

Large and positive

26
Q

Expression for magnetization of a ferromagnetic substance

A

B= μo (1+χ) H

27
Q

Expression for relative magnetic permeability of a substance

A

μr= 1+ χ

28
Q

What are diamagnetic substances?

A

Substances that are weakly repelled by a magnet are called diamagnetic substances.

29
Q

How does a diamagnetic substance align itself when suspended freely in magnetic field?

A

It aligns itself at right angles to the direction of field.

30
Q

Define superconductors

A

Superconductors are metals which when cooled to very low temperatures exhibit both perfect conductivity perfect diamagnetism.

31
Q

What is Messiner effect?

A

The phenomenon of perfect diamagnetism in superconductors is called the Messiner effect.

32
Q

Properties of diamagnetic substances

A

Pg250

33
Q

Examples of diamagnetic substances

A

Ag, Pb, Si, N2, NaCl, Bi, Cu, Sb, Au, Hg, H2O, air, H2

34
Q

What are paramagnetic substances?

A

Substances which are weakly attracted by a magnet are called paramagnetic substances.

35
Q

What are atomic magnets?

A

In paramagnetic substance, the magnetic dipole moments of all the electrons do not cancel out resulting in some dipole moment for an atom so that each atom of a paramagnetic substance is equivalent to tiny magnetic dipole called atomic magnets.

36
Q

Give reasons: Atomic magnets cannot be used to make permanent magnets.

A

Lose their magnetism on removal of external electric field.

37
Q

List the properties of paramagnetic substances.

A

Pg 251

38
Q

What happens when a thin rod of paramagnetic substance is freely suspended in magnetic field?

A

Comes to rest with length parallel to direction of external electric field.

39
Q

Examples of paramagnetic substances

A

Al, Mn, Cr, Pt, O2, Na, Ca, Li, CuCl2, W, Nb, etc

40
Q

How does the susceptibility of a paramagnetic substance depend on temperature?

A

The susceptibility of a paramagnetic substance varies inversely with temperatures.
χ α 1/Τ

41
Q

What are ferromagnetic substances?

A

Substances which are strongly attracted by a magnet are known as ferromagnetic substances.

42
Q

Give reasons: Permanent magnets are made of ferromagnetic substances.

A

Retain magnetism even after removal of external magnetic field.

43
Q

Properties of ferromagnetic substances

A

Pg 251

44
Q

How does a thin rod of ferromagnetic substance in an external magnetic field align itself?

A

Comes to rest with axis parallel to magnetic induction between two poles.

45
Q

Define domains

A

The region of a ferromagnetic substance on which all magnetic moments are aligned in the same direction are known as domains.

46
Q

Give reasons: all Magnetic dipoles have magnetic dipole moments in the same direction

A

Strong exchange coupling between neighboring atoms in domain.

47
Q

What is flipping or domain rotation?

A

When external applied magnetic field to a ferromagnetic substance is large, the dipole moments of non-alliance dipoles rotate in the direction of applied field. This process is known as flipping or domain rotation.

48
Q

Does temperature affect degree of magnetization of a ferromagnetic substance?

A

Yep

49
Q

Explain domain theory.

A

Pg 252

50
Q

Define curie temperature

A

The temperature at which domain structure is destroyed and the ferromagnetic system looses its magnetism and above which a ferromagnetic substance is converted into a paramagnetic substance is called Curie Temperature.

Std 12 PHYSICS (12 decks)

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