Question

Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.
A. Yes, in space there is enough air for travelling sound
B. No, there is a vacuum in space.
C. Yes, no gravity in space
D. None of these

Answer 1

Hint:Sound waves need molecules to propagate as they are longitudinal waves, so they need a medium to travel through. The molecules vibrate and thus pass the vibration of sound from one molecule to another, and thus propagate through either compression or rarefaction.

Complete answer:
 We know that sound waves are longitudinal waves. Longitudinal waves need a medium to travel. Longitudinal waves are transported through particles. For sound waves, they travel through compression and rarefaction. They travel through different sequences of waves of pressure through a compressible media. Sounds can propagate through different media of solid, liquid and gas. Sound waves travel by vibrations of molecules. In fact, when sound travels through different types of media, its speed changes. When sound travels in solid, its speed is more when comparing the speed of sound with respect to liquid and gas.
This is because the density of solids is more; hence the molecules are nearer to each other. Because the molecules are nearer, they collide with each other more frequently; hence the numbers of vibrations are more, so the sound travels faster in denser substances. Thus the speed of sound in air is slower as compared to solids and liquids.
Now, when the two astronauts are floating close to each other in space, without the use of any special device, they cannot talk to each other because there is vacuum between them. As there is vacuum, it means there are no molecules or particulate matter between them for the sound to travel. So they cannot talk to each other.

Hence option B is the correct one.

Note: For astronauts to be able to talk in space, they use special radio devices. These radio devices are in-built into the astronaut’s helmet, and in this way, the astronauts are able to talk in space. It is impossible for sound to travel in space, because there is no medium, hence we are not able to hear explosions in the Sun.