Two material bars A and B of equal area of cross-section, are connected in series to a DC supply. A is made of usual resistance wire and B of an n-type semiconductor.
(a) In which bar is drift speed of free electrons greater?
(b) If the same constant current continues to flow for a long time, how will the voltage
drop across A and B be affected? Justify each answer.
Answers
Answer:
a) As we know that the drift velocity depends on the current as,
Where n is the no. of charge carriers per unit volume, e is the charge of an electron, I is the current flowing and A is the area of cross section of the resistance.
As we know that,
nmetals>nsemiconductors
so, for the same value of current and same area of cross-section the drift velocity of electrons in metal resistance is smaller than in the n-type semiconductor.
b) If the same constant current continues to flow for a long time, the voltage drop across A will increase as the resistance of metal increases with increase in temperature but will decrease in B as the resistance of a semiconductor decreases with increase in temperature.
Answer:
(a) Drift speed in B (n-type semiconductor) is higher
(b) Voltage drop across A will increase as the resistance of A increases with increase in temperature. Voltage drop across B will decrease as resistance of B will decrease with increase in temperature.
Explanation:
(a)Reason: I = neAvd is same for both n is much lower in semiconductors.