Question:
Assertion [A]: For light diverging from a point source, the intensity at the wavefront does not depend on the distance.
Reason [R]: In a diverging beam of light from a point source, spherical wavefront is observed.
Assertion [A]: For light diverging from a point source, the intensity at the wavefront does not depend on the distance.
Reason [R]: In a diverging beam of light from a point source, spherical wavefront is observed.
Reason [R]: In a diverging beam of light from a point source, spherical wavefront is observed.
Show Hint
For a point source, intensity decreases with distance (\(I \propto 1/r^2\)) even though wavefronts are spherical.
Updated On: Jul 18, 2026
- and (R) are true and (R) is the correct explanation of (A).
- Both (A) and (R) are true, but (R) is not the correct explanation of (A).
- is true but (R) is false.
- is false but (R) is true.
Show Solution
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The Correct Option is D
Solution and Explanation
Step 1: Understand the assertion.
Assertion states that intensity does not depend on distance for a diverging point source. This is incorrect because intensity decreases with square of distance: \(I \propto 1/r^2\).
Step 2: Understand the reason.
Reason states that the wavefront of light from a point source is spherical. This is true.
Step 3: Relation between assertion and reason.
While the reason is correct, it does not justify the assertion. The intensity decreases with distance even for spherical wavefronts.
Step 4: Evaluate truth values.
\[ \text{A is false}, \quad \text{R is true} \]
Step 5: Option analysis.
Option (4) matches the truth values: Assertion false, Reason true.
Step 6: Final conclusion.
Hence, correct option is:
\[ \boxed{(A) \text{ is false but (R) is true}} \]
Assertion states that intensity does not depend on distance for a diverging point source. This is incorrect because intensity decreases with square of distance: \(I \propto 1/r^2\).
Step 2: Understand the reason.
Reason states that the wavefront of light from a point source is spherical. This is true.
Step 3: Relation between assertion and reason.
While the reason is correct, it does not justify the assertion. The intensity decreases with distance even for spherical wavefronts.
Step 4: Evaluate truth values.
\[ \text{A is false}, \quad \text{R is true} \]
Step 5: Option analysis.
Option (4) matches the truth values: Assertion false, Reason true.
Step 6: Final conclusion.
Hence, correct option is:
\[ \boxed{(A) \text{ is false but (R) is true}} \]
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