Question

State which law determines the direction of magnetic field around a current carrying wire.
A). Right hand thumb rule
B). Left hand thumb rule
C). Right hand index rule
D). Left hand index rule

Answer 1

Consider a current carrying wire. With the help of a compass obtain the direction of the magnetic field and then compare it with the given rules with the question. Only one rule will give the same direction as the compass. That will be our answer.

_Complete step-by-step answer: _
Consider a wire carrying current through it. The flow of charges will produce a magnetic field around it. If we bring a compass near it we can feel the magnetic field around it because the compass will direct us in the direction of the magnetic field produced due to this current carrying wire.
Direction of the magnetic field depends on the direction of flow of current through the wire. The direction is given by the right-hand thumb rule. If we curl up our finger around the current carrying wire with our thumb in the direction of the flow of current through the wire, the direction of the magnetic field will be the same direction in which direction our fingers are curled up.

So, the direction of magnetic field due to a current carrying wire is given by the right-hand thumb rule.
The correct option is (A).

Note: Around a current carrying wire we get magnetic fields as concentric circles. The magnitude of the magnetic field around the wire is given by the Biot-Savart law.
Mathematically, $B=\dfrac{{{\mu }_{0}}I}{2\pi r}$, where I is the current flowing through the wire and r is the shortest distance to wire from the point where we will measure the magnetic field. ${{\mu }_{0}}$ is called the permeability of free space.