Two astronauts on the moon are standing 10 m apart. Astronaut A shouts toward Astronaut B and simultaneously flashes a light signal. Which of the following statements is correct?

Correct option is D

The correct answer is (d) The light signal from Astronaut A will reach Astronaut B but not the sound.
Explanation:
• Sound is a mechanical wave that requires a material medium (solid, liquid, or gas) to travel through.
• The Moon has no atmosphere; it is essentially a vacuum. Therefore, sound waves cannot travel from one astronaut to another because there are no air molecules to vibrate.
• Light is an electromagnetic wave, which does not require any medium and can travel through a vacuum at its maximum speed (m/s).
• Consequently, while the light signal will reach Astronaut B almost instantaneously, the shout will not be heard at all.
• This is a fundamental concept in NCERT Physics (Class 9), which explains that sound cannot travel in a vacuum.
Information Booster:
• Astronauts communicate on the moon using radio waves, which are also electromagnetic waves and can travel through the vacuum of space.
• In contrast to sound, the speed of light in a vacuum is a universal constant, allowing visual and electronic signals to be transmitted between lunar explorers and Earth.
Additional Knowledge:
(a) Both sound and light reach Astronaut B... (Incorrect)
• This statement is false because it assumes sound can travel through a vacuum. On Earth, this would be true, but on the Moon, the lack of air prevents sound propagation.
(b) Both reach at equal speed (Incorrect)
• This is scientifically incorrect. Even in a medium where both travel, the speed of light is significantly faster than the speed of sound (e.g.,
m/s for sound vs. m/s for light in air).
(c) Neither sound nor light will reach... (Incorrect)
• This is false because light is not blocked by a vacuum. The moon's environment does not stop the transmission of light or any other electromagnetic radiation.