If we are given direction of current,
How do we find Direction of Magnetic Field?
We find Direction of Magnetic Field using Maxwell's Right-hand Thumb Rule
Suppose we hold an electric wire with our right hand as show below
Assuming current flows in direction of thumb (from bottom to top)
Direction of Magnetic field will be in Direction in which our finger curl (from from Left to Right Direction)
Hence,
when current flows from bottom to top, magnetic field is anticlockwise
There's another method which we can use - Maxwell's Corkscrew Rule
Maxwell Corkscrew rule
What is a Corkscrew?
A corkscrew is a device which is used to pull cork from bottle
It contains a spiral metal rod and a handle
To find magnetic field using corkscrew rule -
When we turn a corkscrew clockwise (from right to left), it goes inside the cork
So, if magnetic field is clockwise, direction of current is inside
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Comparing Right hand Thumb Rule and Corkscrew Rule
| Right Hand thumb rule | Corkscrew rule |
|
Suppose we are holding a straight current carrying wire in our right hand.
Point the thumb in the direction in which the current is flowing The direction in which our fingers curl is the direction of the magnetic field. |
Suppose we have a corkscrew.
Point the pointed tip of the corkscrew in the direction in which the current is flowing. The direction in which the screw rotates (clockwise) is the direction of the magnetic field. |
Summary
| Flow of Current | Magnetic Field Direction |
| Bottom to Top | Clockwise (Left to Right) |
| Top to Bottom | Anticlockwise (Right to Left) |
Questions
NCERT Question 6 (c) - State whether the following statements are true or false.
The field at the centre of a long circular coil carrying current will be parallel straight lines.
NCERT Question 15 (i) - State the rule to determine the direction of a
(i) magnetic field produced around a straight conductor-carrying current,
