PHYSICS MASTERY NOTES: MAGNETISM &
INDUCTION
1. Moving Coil Galvanometer
Introduction: A device used to detect and measure small electric currents in a circuit.
Construction
▪Ferromagnetic Material: Used as the core to increase magnetic flux.
▪Cu Wire: Copper wire wound on a rectangular frame.
▪Magnetic Poles: Placed between two strong magnetic poles to ensure τis maximum.
▪Restoring Torque: Provided by a spring mechanism.
Working
Consider a rectangular frame ABCD in which equal and opposite forces are applied. The net force on
the frame is zero, but the couple of forces produces torque in the frame.
Torque (Deflecting) = NIAB — (1)
As flow of current through the rectangular frame stops, restoring torque in the spring takes the
rectangular frame back to its original position.
Restoring Torque = kϕ — (2)
Where:
k = Spring constant
ϕ = Angle of rotation
Comparing Eqn (1) & (2):
Torque = RestoringTorque
NIAB = kϕ
I = (k / NAB) * ϕ
Physics Mastery Series | Comprehensive Study Notes
, 2. Magnetic Dipole Moment
Weknowthattorqueisproducedinthecaseofcurrent flowing in a conductor.
τ=P×E
Where:
P = Electric dipole moment
E = Electric Field
Similarly, if we put the same apparatus in an external magnetic field:
τ=M×B
Where M is the Magnetic Dipole Moment.
3. Magnetic Potential Energy of Dipole
Byanalogywith electrostatics:
▪ Electric Potential Energy =P · E
▪ Magnetic Potential Energy =M · B
4. Bio-Savart Law (V. Imp)
Themagnitudeofmagneticinductionatapoint due to a small element of a current-carrying
conductor is:
▪i) Directly proportional to the current (I).
▪ii) Directly proportional to the length of the element dl( ).
Physics Mastery Series | Comprehensive Study Notes
INDUCTION
1. Moving Coil Galvanometer
Introduction: A device used to detect and measure small electric currents in a circuit.
Construction
▪Ferromagnetic Material: Used as the core to increase magnetic flux.
▪Cu Wire: Copper wire wound on a rectangular frame.
▪Magnetic Poles: Placed between two strong magnetic poles to ensure τis maximum.
▪Restoring Torque: Provided by a spring mechanism.
Working
Consider a rectangular frame ABCD in which equal and opposite forces are applied. The net force on
the frame is zero, but the couple of forces produces torque in the frame.
Torque (Deflecting) = NIAB — (1)
As flow of current through the rectangular frame stops, restoring torque in the spring takes the
rectangular frame back to its original position.
Restoring Torque = kϕ — (2)
Where:
k = Spring constant
ϕ = Angle of rotation
Comparing Eqn (1) & (2):
Torque = RestoringTorque
NIAB = kϕ
I = (k / NAB) * ϕ
Physics Mastery Series | Comprehensive Study Notes
, 2. Magnetic Dipole Moment
Weknowthattorqueisproducedinthecaseofcurrent flowing in a conductor.
τ=P×E
Where:
P = Electric dipole moment
E = Electric Field
Similarly, if we put the same apparatus in an external magnetic field:
τ=M×B
Where M is the Magnetic Dipole Moment.
3. Magnetic Potential Energy of Dipole
Byanalogywith electrostatics:
▪ Electric Potential Energy =P · E
▪ Magnetic Potential Energy =M · B
4. Bio-Savart Law (V. Imp)
Themagnitudeofmagneticinductionatapoint due to a small element of a current-carrying
conductor is:
▪i) Directly proportional to the current (I).
▪ii) Directly proportional to the length of the element dl( ).
Physics Mastery Series | Comprehensive Study Notes
