**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

dF_{m} = 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 I_{1} and I_{2} 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.