## Magnetic effect of electric current

### Magnetic effect of electric current

1) This effect was the first discovered by Oested in 1820.

2) Magnetic effect of current is a phenomenon by virtue of which an electric current in a conductor produces a magnetic field around it.
3) The magnitude of the magnetic field produced depends upon the magnitude of current passing through conductor.
4) The direction of magnetic field produced depends upon the direction of current in the conductor.
5) The magnetic field produced due to a current carrying conductor is always in a plane perpendicular to the plane of the conductor.

6) When an electric current is passing through a conductor only magnetic field is associated with the conductor but there is no electric field, since the conductor is electrically neutral.

7) When an electric charge is moving in free space, both, electric and magnetic fields are produced, whereas a static charge produced only electric field. It means, a stationary charge cannot produce a magnetic field.
8) The source of magnetic fields are:
a) Current carrying conductor
b) Changing electric field moving charged particle
c) Permanent magnet and electromagnet etc.
9) A magnetic field interacts with the moving charges only. For stationary charges, its effect is zero.

10) The current element of a current carrying conductor is equal to the product of current I and elementary length dl of the current carrying conductor. Thus current element is given by I dl. The direction of current element is tangent to the element and is in the direction of current flow in the conductor.

### Hall effect

Hall effect states that if a magnetic field is applied perpendicular to a metal plate carrying current, a transverse voltage is set up at right angles to both the current and the magnetic field between those points on the opposite face of the plate, which in the absence of the field where at the same potential.

### Natural magnet

1) Attract small pieces of iron, cobalt and nickel towards it.

2) When suspended freely, comes to rest along north-south direction. The end pointing towards geographic north is called North Pole and the end pointing towards geographic south is called South Pole. The magnets which are prepared artificially are called artificial magnets. For example, a bar magnet, a magnetic needle, horse shoe magnet, electromagnet are all artificial magnets.

### Tangent law

When a magnet is suspended freely under the combined action of two uniform magnetic fields of intensities F and H acting at 90° to each other, the magnet comes to rest making angle θ with the direction of H, such that F = H tan. This is tangent law. A tangent galvanometer is based on tangent law. It is an instrument, which is used for direction and measurement of electronic current. The vertical coil of tangent galvanometer is set in magnetic meridian. When a current I is passed through n turns of this coil heaving radius r, a uniform magnetic field F is produced at the centre of coil, perpendicular to the plane of the coil, i.e. at 90 degree to horizontal component H of earth’s magnetic field. The magnetic needle of tangent galvanometer registers a definition Θ under the combined influence of crossed magnetic fields F and H.

### Vibration Magnetometer

It is used to comparing magnetic moments of two magnets and also far comparing the horizontal component of earth’s field at two places. The time period T of vibration of a magnet of magnetic moment M and moment of inertia I under horizontal component of earth’s field (H) is given by T=2π