Assertion (A): Hall effect is used to find the type of semiconductor. Reason (R): When a specimen of semiconductor carrying current I lies in a magnetic field the force on electrons and holes is in opposite directions.

ANS:A - Both A and R are true and R is correct explanation of A

When a current. Carrying semiconductor is placed in a magnetic field charge inside the semiconductor experience a force which is perpendicular to both magnetic field and current.

Here,
Lorenz force( f) = q *( v * B) ----> (1)
In a semiconductor electric field is also present due to electrons so electric force.
F(e)= q E ----> (2)

Solving ...
V*B = E ----> (3)
Since E= v/t
V*B=v/t ----> (4)
Since, J = q * n * v
V = J/q*n .. Substitute in eq 4.
VB = (J/qnt)
Since, J = current (i)/ Area of semiconductor(A)

A= thickness of semiconductor * width of the semiconductor
A= w * t
J = I / w t
So;
( I * B )/(w q n) = V. Hall voltage
Hall coefficient R=(1/ qn )
R = v * w / (B * I )
R is inversely proportional to I and B.

For n-type semiconductor, electrons accommodate at bottom of a semiconductor due to opposite force.

For p-type semiconductor, electrons accommodate at top of the semiconductor.