Question 21:
easyAssertion (A): If X-ray is allowed to fall on uncharged gold leaf in evacuated glass chamber of electroscope, leaves will diverge.
Reason (R): Uncharged gold leaves will get charged positively when x-ray falls on it.
X-rays have sufficient energy to eject electrons from the gold leaves (photoelectric effect), leaving them positively charged. The like positive charges on the leaves cause them to repel and diverge. Thus, (R) correctly explains (A).
Question 22:
easyAssertion (A): Excess charge on a conductor resides entirely on the outer surface.
Reason (R): Like charges repel each other.
Assertion (A) is true. Excess charges on a conductor spread out on the outer surface due to mutual repulsion. Reason (R) is also true, as like charges repel. (R) correctly explains (A).
Question 23:
easyIf a soap bubble contracts, the pressure inside bubble
The excess pressure inside a soap bubble is \(\Delta P = \frac{4T}{r}\). When it contracts, its radius \(r\) decreases, leading to an increase in the excess pressure, hence the total internal pressure increases.