Assertion (A): The drift speed of electrons in metals is small (in the order of a few \(mm/s\)) and the charge of an electron is also very small (\(= 1.6 \times 10^{-19}\text{ C}\)), yet we can obtain a large current in a metal.
Reason (R): At room temperature, the thermal speed of electron is very high (about \(10^7\) times the drift speed).
(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false
Solution:
Despite small drift speed \(v_d\) and electron charge \(e\), metals have a very high number density \(n\) of free electrons. This high \(n\) allows for large current \(I\). Thermal speed is irrelevant to the magnitude of current. So, A is true, R is true, but R does not explain A.
Leave a Reply