Important Notes - Magnetic Effects of Electric Current - JEE Main by ednexa.com

1. Magnetic effect of electric current

2. Oersted’s Experiment
1. Every
current
carrying
conductor
has
associated magnetic field and
2. Direction of the magnetic field at a point is
perpendicular to
a. Length of the conductor and

3. b. The line joining the conductor and the
given point.
Features of Magnetic Field
1. Strength of the magnetic field at a point
near
a
current
carrying
conductor
is
inversely proportional to the distance of the
point from the conductor.
2. Strength of the magnetic field at a point
near a current carrying conductor is directly
proportional
to the magnitude of current flowing through
the conductor.
3. Direction of the magnetic field at a point
near a current carrying conductor depends
on the direction of the current flowing
through the conductor. If the direction of the

4. conductor is reversed, direction of the
magnetic field reverses.
Right Hand Rule
„imagine the current carrying conductor to be
held in your right hand, with the thumb
outstretched and the fingers curled round it. In
this situation, if the thumb indicates the

5. direction of current, the curled fingers indicate
the direction of the magnetic field around it.‟
Magnetic Induction
The vector quantity used to describe the
magnetic field is called magnetic induction (B).
“Magnetic induction at a point is the magnetic
flux density at that point.”
Hence the unit of magnetic induction is
2
2
weber/m (Wb/m ).

6. Biot Savart’s Law or Laplace’s Law
The magnitude of magnetic induction at a point
neat a current carrying conductor due to small
element of the conductor of length dℓ carrying
current I, at distance r from the element is
directly proportional to a. current
I
flowing
through the element

7. b. length of the element dℓ
c. sine of angle θ between the element and
the line joining the midpoint of the element
to the given point and inversely proportional
to square of the distance between the
midpoint of the element and the given point.
The figure shows a conductor carrying
current I.
According to Biot - Savart‟s law the small
magnetic induction dB a P is given as
I d sin
r2
dB
0
dB
4
Id sin
r2
where
0
4
is a constant whose value is 10
In vector form
dB
0
4
Id u
r2
–7
Wb / Am

8. According to right hand rule, the direction of
dB is perpendicular to plane of paper
directed inwards.
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