# How to find the direction of Magnetic field? Thumb rule

Scientist Hans Christian Oersted first observed the deflection of a magnetic needle or compass placed near a current carrying wire. This concludes that the current carrying wire can produce a magnetic field around it. In another article, we have discussed the Origin, definition, unit and dimension of magnetic field. Since, the magnetic field is a vector quantity, it will have a direction. In this article, we are going to discuss all possible methods to find the direction of magnetic field due to a current carrying conductor or wire.

There are four different ways to find the direction of magnetic field. These are –

• by observing the deflection of magnetic needle
• Ampere’s swimming rule
• SNOW rule
• Fleming’s thumb rule

## How to find the direction of magnetic field by a magnetic needle or compass?

If we place a magnetic needle in a magnetic field, the needle deflects. The direction of the deflection of north pole of the needle gives the direction of the magnetic field in that region. This is the first and the oldest method to determine the direction of magnetic field.

## Ampere’s swimming rule

One can determine the direction of the magnetic field vector by using Ampere’s swimming rule. This rule is named after Scientist Ampere.

Ampere’s swimming rule states that if a man swims in the direction of current flow through the wire keeping a magnetic needle below him then the north pole of the needle will be deflected along the left hand of the man. That means the direction of the magnetic field below the man or the wire is along the left side of the man. But at any point upside the wire, the deflection of the needle will be towards right hand of the man.

## SNOW rule

SNOW rule is the alternative version of the Ampere’s swimming rule. This rule is used rarely.

This rule states that if the current flows through the wire in the direction from South to North keeping the magnetic needle over it, then the north pole of the needle deflects towards west direction.

## Fleming’s Thumb rule to find the direction of magnetic field

The best way to find the direction of magnetic field due to a current carrying conductor is by using Fleming’s right hand thumb rule. This rule is also known as the right hand grip rule.

Fleming’s right hand thumb rule states that if one holds a current carrying in his right hand such that the thumb finger points the direction of current flow through the wire then the curled fingers of the right hand indicate the direction of magnetic field.

Warning: the holding of current carrying wire is an imagination. Don’t do this practically. It may damage your health, higher current gives higher shock.

In this article, we learned how to find the direction of magnetic field produced by a current carrying wire or conductor. This is all from this article. If you have any doubt on this topic you can ask me in comment section.

Thank you!

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