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Physics Notes for Class 12 Chapter 4 Moving
Charges and Magnetrism
Oersted’s Experiment
A magnetic field is produced in the surrounding of any current carrying conductor.
The direction of this magnetic field can be obtained by Ampere’s swimming rule.
SI unit of magnetic field is Wm-2 or T (telsa).
The strength of magnetic field is called one tesla, if a charge of one coulomb, when moving
with a velocity of 1 ms-1 along a direction perpendicular to the direction of the magnetic field
experiences a force of one newton.
1 tesla (T) = 1 weber metre-2 (Wbm-2)
= 1 newton ampere-1 metre-1 (NA-1 m-1)
CGS units of magnetic field are called gauss or oersted.
1 gauss = 10-4 tesla.
Maxwell’s Cork Screw Rule
If a right handed cork screw is imagined to be rotated in such a direction that tip of the screw
points in the direction of the current, then direction of rotation of thumb gives the direction of
magnetic line of force.
The conventional sign for a magnetic field coming out of the plane and normal to it is a dot i.e.,
The magnetic field perpendicular to the plane in the downward action is denoted by ®.
Ampere’s Swimming Rule
If a man is swimming along the wire in the direction of current his face turned towards the
needle, so that the current enters through his feet, then north pole of the magnetic needle will
be deflected towards his left hand.
Magnetic Field
The space in the surrounding of a magnet or any current carrying conductor in which its
magnetic influence can be experienced.
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Biot Savart’s Law
The magnetic field produced by a current carrying element of length dl, carrying current I at a
point separated by a distance r is given by
dB = μo / 4 π Idl * r / r3
or dB = μo / 4 π Idl sin θ / r2
where, θ is the angle between the direction of the current and μo is absolute permeability of the
free space.
SI unit of magnetic field is Wm-2 or (tesla) and CGS unit of magnetic field is gauss or oersted 1
gauss = 10-4tesla.
The direction of magnetic field dB is that of I dl * r .
Magnetic Field Due to a Straight Current Carrying Conductor
where φ1 and φ2 are angles, which the lines joining the two ends of the conductor to the
observation point make with the perpendicular from the observation point to the conductor.
For infinite length conductor and observation point is near the centre of the conductor,
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Physics Notes for Class 12 Chapter 4 Moving
Charges and Magnetrism
Oersted’s Experiment
A magnetic field is produced in the surrounding of any current carrying conductor.
The direction of this magnetic field can be obtained by Ampere’s swimming rule.
SI unit of magnetic field is Wm-2 or T (telsa).
The strength of magnetic field is called one tesla, if a charge of one coulomb, when moving
with a velocity of 1 ms-1 along a direction perpendicular to the direction of the magnetic field
experiences a force of one newton.
1 tesla (T) = 1 weber metre-2 (Wbm-2)
= 1 newton ampere-1 metre-1 (NA-1 m-1)
CGS units of magnetic field are called gauss or oersted.
1 gauss = 10-4 tesla.
Maxwell’s Cork Screw Rule
If a right handed cork screw is imagined to be rotated in such a direction that tip of the screw
points in the direction of the current, then direction of rotation of thumb gives the direction of
magnetic line of force.
The conventional sign for a magnetic field coming out of the plane and normal to it is a dot i.e.,
The magnetic field perpendicular to the plane in the downward action is denoted by ®.
Ampere’s Swimming Rule
If a man is swimming along the wire in the direction of current his face turned towards the
needle, so that the current enters through his feet, then north pole of the magnetic needle will
be deflected towards his left hand.
Magnetic Field
The space in the surrounding of a magnet or any current carrying conductor in which its
magnetic influence can be experienced.
www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)
, 2|Page
Biot Savart’s Law
The magnetic field produced by a current carrying element of length dl, carrying current I at a
point separated by a distance r is given by
dB = μo / 4 π Idl * r / r3
or dB = μo / 4 π Idl sin θ / r2
where, θ is the angle between the direction of the current and μo is absolute permeability of the
free space.
SI unit of magnetic field is Wm-2 or (tesla) and CGS unit of magnetic field is gauss or oersted 1
gauss = 10-4tesla.
The direction of magnetic field dB is that of I dl * r .
Magnetic Field Due to a Straight Current Carrying Conductor
where φ1 and φ2 are angles, which the lines joining the two ends of the conductor to the
observation point make with the perpendicular from the observation point to the conductor.
For infinite length conductor and observation point is near the centre of the conductor,
www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)
