Two astronauts on the Moon are standing 10 m apart. Astronaut A shouts towards Astronaut B and at the same time flashes a light signal. Which of the following statements is correct?
- ABoth the sound and the light from Astronaut A will reach Astronaut B, but the light will arrive slightly earlier.
- BBoth the sound and the light from Astronaut A will reach Astronaut B at equal speed.
- CNeither the sound nor the light from Astronaut A will reach Astronaut B.
- DThe light signal from Astronaut A will reach Astronaut B, but not the sound.
Show answer and explanation
Correct answer: (d) The light signal from Astronaut A will reach Astronaut B, but not the sound.
Explanation
The Moon has no atmosphere, so there is no air to carry sound. Sound is a mechanical wave and needs a medium, so the shout will not reach Astronaut B through the empty space.
Light is an electromagnetic wave and needs no medium, so the light signal reaches Astronaut B. This is why astronauts talk to each other by radio, which also travels as electromagnetic waves.