Question

Assertion: 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 $ \left( { = 1.6 \times {{10}^{ - 19}}C} \right) $ , yet we can obtain a large current in a metal.
Reason: At room temperature, the thermal speed of electrons is very high (about $ {10^7} $ times the drift speed).
 $ \left( A \right) $ Both assertion and reason are correct and reason is the correct explanation for assertion.
 $ \left( B \right) $ Both assertion and reason are correct and reason is not the correct explanation for assertion.
 $ \left( C \right) $ Assertion is correct but reason is incorrect.
 $ \left( D \right) $ Assertion is incorrect but reason is correct.

Answer 1

Hint: As we know that a drift velocity is an average velocity accomplished by charged atoms, such as electrons, in a material owing to an electric field. Therefore, by using this statement we can understand the drift velocity, and then we can choose the correct answer for it.

Complete Step By Step Answer:
So we have the assertion given as 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. And the reason which we have in the question is incorrect.
The reason behind it is, due to the heaviness in the electron density they obtain a large current.
Hence, we can say from this that reason is not the correct explanation for the statement.
Therefore, the option $ \left( B \right) $ is correct.

Note:
Since the value of the thermal velocity is very high and it can be in the order of $ {10^5}m{s^{ - 1}} $ and because of the arbitrary motion of electrons all likely direction their ordinary thermal velocity goes out to be zero. Hence, thermal velocity doesn't subsidize any remaining current.