Physics
Assertion (A) : Longer wires have greater resistance and the smaller wires have lesser resistance.
Reason (R) : Resistance of a wire increases with increase in temperature.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Answer
both A and R are true and R is not the correct explanation of A
Explanation
Assertion (A) is true because the number of collisions suffered by the moving electrons will be more if they have to travel a longer distance in a wire, therefore, a long wire offers more resistance than a short wire (i.e., resistance of a wire ∝ length of wire).
Reason (R) is true because if the temperature of wire increases, electrons in it vibrate more violently. As a result, the number of collisions increases and hence the resistance of wire increases (i.e., the resistance of a wire increases with the increase in its temperature).
The assertion talks about wire length, but the reason explains the effect of temperature. So, although both statements are true, the reason does not explain the assertion.
Related Questions
Assertion (A) : A thick wire offers less resistance in comparison to a thin wire.
Reason (R) : Resistance of wire is directly proportional to its area of cross-section.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A) : Current flows from body at higher potential to a body at lower potential.
Reason (R) : The direction of flow of electrons is from low potential body to a body at a higher potential.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Two copper wires of equal length but different thickness are connected one by one to the same cell and bulb.
(a) In which wire will the rate of flow of the charge be greater? Give reason.
(b) Does a higher current mean that electrons move faster from the battery to the bulb?
(c) If current flows for a longer time, what happens to the charge passing per second? What happens to the total charge transferred?
A student connects a bulb to a cell using two wires, but the bulb does not glow. On checking, the bulb is found to be in proper condition. On further inspection, a wire is found to be loose.
(a) Why did the bulb not glow even though it was not faulty?
(b) What is meant by a closed circuit?
(c) Why is electric current considered as a flow of charges?
(d) What is the conventional direction of electric current?