Question

There are two boxes A & B. Cell phones are kept in both the boxes, all air is sucked from box A and then closed by a device. While box B is simply closed by a device without sucking air from it. A call is made simultaneously on both the phones, but the sound comes only from box B. This is because

Statement 1: In box B there are air particles to vibrate but in box A there is a vacuum

Statement 2: Sound needs a medium for propagation

Answer 1

1. The sound wave is a mechanical wave.
2. Waves that require a medium (solid, liquid, gas) to travel are called mechanical waves.
3. In box A, the air is sucked from it. Due to this, a vacuum is created inside and the sound does not propagate.
4. In box B, as it contains air, the sound has a medium to travel and hence we can hear the sound from this box.

Hence both the statements are correct explanations for this case.