NEET Physics Notes Magnetic Effects of Current-Magnetic Force on a Current Carrying Conductor
Magnetic Force on a Current Carrying Conductor
Magnetic Force on a Current Carrying Conductor
If a current carrying conductor is placed in a magnetic field B, then a small current element I dl experiences a force given by
dFm = Idl x B
and the total force experienced by whole current carrying conductor will be
The direction of force, when current element M and B are perpendicular to each other can also be determined by applying Fleming’s left hand rule or Right hand thumb rule.
Force between Two Parallel Current Carrying Conductors
Two parallel current carrying conductors exert magnetic force on one another.
If two infinitely long parallel conductors carry currents I1 and I2 respectively, and are separated by a distance r, then magnetic force experienced by length 1 of any one conductor due to the other current carrying conductor is
Current Loop as a Magnetic Dipole
A current carrying loop (of any shape) behaves as a magnetic dipole whose magnetic moment is given by M = IA, where I is. the current flowing through the loop and A the surface area of the loop.
If we have a current carrying coil having N turns, then magnetic moment M of dipole will be M = NIA.
Magnetic moment of a current carrying coil is a vector and its direction is given by Right hand thumb rule.
Torque
When a current carrying loop placed in uniform magnetic field, it experience torque
where, NiA is defined as the magnitude of the dipole moment of the coil (pm).
Moving Coil Galvanometer (MCG)
MCG is used to measure the current upto nanoampere.
In MCG, the coil is suspended between the pole pieces of a strong horseshoe magnet.
The pole pieces are made cylindrical and a soft iron cylindrical core is placed within the coil without touching it. This makes the field radial.
In the plane of the coil always remain parallel to the field. Therefore, θ= 90° and the deflecting torque always has the maximum value
A restoring torque is setup in the suspension fibre. If α is the angle of trust, the restoring torque is
where, K is galvanometer constant.
Some Important Concepts Related to Moving Coil Galvanometer
Some of the important concepts related to galvanometer, i.e. current sensitivity, voltage sensitivity and some of conversions used in galvanometer are given below.
Conversion of Galvanometer into Ammeter
An ammeter is made by connecting a low resistance S in parallel with a pivoted type moving coil galvanometer G. S is known as shunt. Then, from circuit
So, S << G, only a small fraction of current goes through the galvanometer.
Conversion of Galvanometer into Voltmeter
A voltmeter is made by connecting a resistor of high resistance B in series with a pivoted type moving coil galvanometer G.
From the circuit,
Current Sensitivity
The current sensitivity of a galvanometer is defined as the deflection produced in the galvanometer per unit current flowing through it.
Voltage Sensitivity
Voltage sensitivity of a galvanometer is defined as the deflection produced in the galvanometer per unit voltage applied to it.
