Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): When lightning strikes, the sound is heard a little after the flash is seen.
Reason (R): The velocity of light is greater than that of sound. In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Whenever both light and sound are produced together (like lightning or fireworks), light is observed first because it travels much faster than sound.

Answer 1

The Correct Option is A

Concept: This question is based on the concept of difference in speeds of light and sound. In physics:
• Light travels extremely fast (\(\approx 3 \times 10^8 \, \text{m/s}\)).
• Sound travels much slower (\(\approx 340 \, \text{m/s}\) in air). Due to this difference, events involving both light and sound are perceived at different times.

Step 1: Analyze Assertion (A). \[ \text{When lightning strikes, the sound is heard after the flash is seen.} \] This statement is true. When lightning occurs:
• The flash (light) reaches our eyes almost instantly.
• The sound (thunder) takes more time to travel through air to reach our ears. Hence, we see the flash first and hear the sound later.

Step 2: Analyze Reason (R). \[ \text{The velocity of light is greater than that of sound.} \] This statement is also true. Numerically: \[ \text{Speed of light} \gg \text{Speed of sound} \]

Step 3: Establish the relationship between (A) and (R).
• Because light travels much faster than sound, it reaches us first.
• Sound, being slower, arrives after a noticeable delay. Thus, the reason directly explains the assertion.

Step 4: Logical conclusion.
• Assertion (A) is true.
• Reason (R) is true.
• Reason (R) correctly explains Assertion (A).

Step 5: Final answer. \[ \boxed{\text{Both (A) and (R) are correct and (R) is the correct explanation of (A)}} \]