Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): When charges \(+Q\) and \(-Q\) are placed at the two ends of a metal cylinder, a steady current flows through the cylinder for a long time.
Reason (R): Cells and batteries are devices that keep a steady electric field in a conductor.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) is not correct but (R) is correct.
Assertion (A) When charges \( +Q \) and \( -Q \) are placed at the two ends of a metal cylinder, a steady current flows through the cylinder for a long time. — False. The field of these charges pushes the free electrons towards \( +Q \). The moving electrons soon neutralise the charges at the ends, and the field inside dies away. So the current lasts only for a very short time.
Reason (R) Cells and batteries are devices that keep a steady electric field in a conductor. — True. A cell keeps making up for the charges that the electrons neutralise. The field in the conductor then stays steady, and so does the current.
NCERT (2026-27):
Electric Currents in Conductors – “… The electrons will be accelerated due to this field towards +Q. They will thus move to neutralise the charges. The electrons, as long as they are moving, will constitute an electric current. Hence in the situation considered, there will be a current for a very short while and no current thereafter.”
Electric Currents in Conductors – “… Mechanisms, which maintain a steady electric field are cells or batteries that we shall study later in this chapter.”