Current loop as a magnetic dipole and its magnetic dipole moment,magnetic dipole moment of a revolving electron, bar magnet as an equivalent solenoid, magnetic field lines, earth's magnetic field and magnetic elements.

1. Revised syllabus -
CORONA PANDEMIC
2020
Chapter–5: Magnetism
and Matter

2. NUMERICALS NCERT
Example 4.13
In the circuit (Fig. 4.27) the current is to be measured. What is the value
of the current if the ammeter shown
(a) is a galvanometer with a resistance RG = 60.00 Ω,
(b) is a galvanometer described in (a) but converted to an ammeter by a
shunt resistance rs = 0.02 Ω
(c) is an ideal ammeter with zero resistance?

3. Question 4.28:
A galvanometer coil has a resistance of 15 Ω and the
metre shows full scale deflection for a current of 4 mA.
How will you convert the metre into an ammeter of
range 0 to 6 A?
• Resistance of the galvanometer
coil, G = 15 Ω
• Current for which the
galvanometer shows full scale
deflection,
• = 4 mA = 4 × 10−3 A
• Range of the ammeter is 0-6A
A shunt resistor of resistance S is
to be connected in parallel with
the galvanometer to convert it
into an ammeter

4. Question 4.27
A galvanometer coil has a resistance of 12 Ω and the
metre shows full scale deflection for a current of 3 mA.
How will you convert the metre into a voltmeter of
range 0 to 18 V?
• Resistance of the
galvanometer coil, G = 12 Ω
• Current for which there is
full scale deflection, = 3 mA
= 3 × 10−3 A
• Range of the voltmeter is 0,
which needs to be
converted to 18 V.
• V = 18 V
SOLUTION

5. MAGNETISM
1. Bar Magnet and its properties
2. Current Loop as a Magnetic Dipole and Dipole Moment
3. Current Solenoid equivalent to Bar Magnet
4. Bar Magnet and it Dipole Moment
5. Coulomb’s Law in Magnetism
6. Important Terms in Magnetism
7. Magnetic Field due to a Magnetic Dipole
8. Torque and Work Done on a Magnetic Dipole
9. Terrestrial Magnetism
10.Elements of Earth’s Magnetic Field
11.Tangent Law
12.Properties of Dia-, Para- and Ferro-magnetic substances
13.Curie’s Law in Magnetism
14.Hysteresis in Magnetism

6. DISCUSS YOUR
OBSERVATIONS

7. Current Loop as a Magnetic Dipole & Dipole
Moment Magnetic Dipole Moment
is
M = I A n
SI unit is A m2.
I
B
A
TIP:
When we look at any one side of the loop carrying current, if the
current is in anti-clockwise direction then that side of the loop
behaves like Magnetic North Pole and if the current is in clockwise
direction then that side of the loop behaves like Magnetic South Pole.

8. MAGNETIC DIPOLE MOMENT OF A REVOLVING
ELECTRON

10. B
I I
xxxxx xx
B
Current Solenoid as a Magnetic Dipole or
Bar Magnet

11. COMPARISON

12. This integration can be done by trigonometric
substitutions. This
exercise, however, is not necessary for our
purpose.
Consider the far axial field of the solenoid,
i.e.,
r >> a and r >> l. Then the denominator is
approximated by

13. The field lines in
magnetism do not
indicate the direction
of the force on a
(moving) charge.

14. One can plot the magnetic field lines by placing a small
magnetic compass needle at various positions and note
its orientation.

15. Many of the diagrams show magnetic field lines (thick lines in the figure)
wrongly. Point out what is wrong with them.
(b) Wrong. Magnetic field lines (like electric field lines)
can never cross each other
(c) Right. Magnetic lines are completely confined within a toroid
(d) Wrong. Field lines due to a solenoid at its ends and outside cannot
be so completely straight and confined; such a thing violates
Ampere’s law. The lines should curve out at both ends, and meet
eventually to form closed loops.
(e) Right. These are field lines outside and inside a bar magnet
(f ) Wrong. These field
lines cannot possibly
represent a magnetic
field.
Look at the upper
region. All the field lines
seem to emanate out of

16. EARTH'S MAGNETISM

17. Earth’s Magnetism is generated by convection currents of molten iron and nickel in the
earth’s core. These currents carry streams of charged particles and generate magnetic
fields.

18. This magnetic field deflects ionising charged particles coming from the sun
(called solar wind) and prevents them from entering our atmosphere.
A hypothetical giant magnetic dipole is supposed to be located at the centre of the earth.
It does-not coincides with the axis of earth. The dipole is tilted by 11.3° with respect to
earth’s axis
There are two north (magnetic north and geographic north) poles and two south
(magnetic south and geographic south) poles located on the poles of the earth. The
magnetic north and magnetic South Pole is the result of the dipole.
Geographic Axis is a straight line passing through the geographical poles of the
earth. It is the axis of rotation of the earth. It is also known as polar axis.
Magnetic Axis is a straight line passing through the magnetic poles of the earth. It
is inclined to Geographic Axis nearly at an angle of 17°
Geographic Equator is a great circle on the surface of the earth, in a plane
perpendicular to the geographic axis. All the points on the geographic equator are
at equal distances from the geographic poles.
IMPORTANT TERMS

19. i) Geographic Meridian at any place is a vertical plane passing through the
geographic north and south poles of the earth.
ii) Magnetic Meridian at any place is a vertical plane passing through the
magnetic north and south poles of the earth.
iii) Magnetic Equator is a great circle on the surface of the earth, in a plane
perpendicular to the magnetic axis. All the points on the magnetic equator
are at equal distances from the magnetic poles.
MAGNETIC
EQUATOR
GEOGRAPHIC
EQUATOR

21. OUR PLACE
FROM
SPACE

22. Declination (θ):
θ
δ
BV
BH
B
Magnetic Meridian
Geographic
MeridianThe angle between the magnetic meridian and
the geographic meridian at a place is Declination
at that place.
It varies from place to place.
Lines shown on the map through the places that
have the same declination are called isogonic
line.
Line drawn through places that have zero
declination is called an agonic line.
Dip or Inclination (δ):
The angle between the horizontal component of
earth’s magnetic field and the earth’s resultant
magnetic field at a place is Dip or Inclination at that
place.
It is zero at the equator and 90° at the poles.
Lines drawn up on a map through places that have
the same dip are called isoclinic lines.
The line drawn through places that have zero dip is
known as an aclinic line. It is the magnetic equator.

23. N
Horizontal Component of Earth’s Magnetic Field (BH ):
The total intensity of the earth’s magnetic field does not lie in any
horizontal plane. Instead, it lies along the direction at an angle of dip (δ)
to the horizontal. The component of the earth’s magnetic field along the
horizontal at an angle δ is called Horizontal Component of Earth’s
Magnetic Field.
BH = B cos δ
Similarly Vertical Component is BV = B sin δ
such that B = √ BH
2 + BV
2
Tangent Law:
If a magnetic needle is suspended in a region
where two uniform magnetic fields are
perpendicular to each other, the needle will
align itself along the direction of the resultant
field of the two fields at an angle θ such that
the tangent of the angle is the ratio of the two
fields.
θ
B2 B
B1
tan θ = B2 / B1

26. ncert numericals

28. 1. Moon,which has no molten core should have ____
magnetic field.
2. Venus has a slower rate of rotation should have
______ (weaker/stronger) magnetic field.
3. Jupiter, which has the fastest rotation rate among
planets and should have ________ magnetic field.
4. Charged particles emitted by the sun flow towards the
earth and beyond, in a stream called the _______.
5. Angle between the true geographic north and the
north shown by a compass needle is called the angle of
zero
weaker
Strong
solar wind.
declination

29. 6. -----------is the angle that the total magnetic field of the earth
makes with the surface of the earth.
7. If the horizontal component of magnetic field is negligible
or zero , the angle of dip is ______
and the magnetic compass which is capable of moving in a
horizontal plane will point in ____________ direction.
8. The magnitude of the field on the earth’s surface ≈
9. 104 G (gauss) =
10. Magnetic moment m is a scalar/vector and
has dimensional formula . It's unit is
DIP
ZERO
ARBITRARY
4 × 10–5
T.
1 T
vector
[L2A] A m2