Physics Group - II (3110018)

BE | Semester-1   Winter-2019 | 02-01-2020

Q4) (a)

Define Hall effect. Give its physical significance.

• When a magnetic field is applied to a current carrying conductor in a direction perpendicular to that of the flow of current, a potential difference or transverse electric field is created across a conductor. This phenomenon is known as Hall Effect.
• By using Hall Effect we can easily identify whether the semiconductor is a p-type or n-type.
• When a voltage is applied to a conductor or semiconductor, electric current starts flowing through it.
• In conductors, the electric current is conducted by free electrons whereas in semiconductors, electric current is conducted by both free electrons and holes.
• The free electrons in a semiconductor or conductor always try to flow in a straight path. However, because of the continuous collisions with the atoms, free electrons slightly change their direction. But if the applied voltage is strong enough, the free electrons forcefully follow the straight path.
• This happens only if no other forces are applied to it in other direction.
• If we apply the force in other direction by using the magnetic field, the free electrons in the conductor or semiconductor change their direction.
• If a magnetic field is applied to this current carrying conductor or semiconductor in a direction perpendicular to that of the flow of current (that is z-direction), an electric field is produced in it that exerts force in the negative y direction (downwards).
• In Hall Effect produced voltage drop determine the type of a material, If the voltage is  positive then the material is said to be p-type and if the voltage produced is negative then the material is said to be n-type.
• Mathematical expression for the Hall voltage is given by:

Where, $\mathrm{B}$ = magnetic field strength
Where, $\mathrm{I}$ = current flowing through the material
Where, $\mathrm{q}$ = charge
Where, $\mathrm{n}$ = number of mobile charge carriers per unit volume
Where, $\mathrm{d}$ = thickness of the material

• So, in order to produce a large Hall voltage we need to use a thin material with few mobile charges per unit volume.