Page 11 - 10-phy-11 Sound

11. Sound eLearn.Punjab

Activity 11.3: Take two identical plastic pipes of suitable Do u Know?
length, as shown in Fig. 11.10 (We can make the pipes
using chart paper). Elephants use low frequency sound waves
• Arrange the pipes on a table near a wall. to communicate with one another. Their
• Place a clock near the open end of one of the pipes large ears enable them to detect these
low frequency sound waves, which have
and try to hear the sound of the clock through the relatively long wavelengths. Elephants
other pipe. can effectively communicate in this way,
• Adjust the position of the pipes so that you can hear even when they are separated by many
the sound of the clock clearly. kilometers.

For your information

By using an oscilloscope, you can “see”
sound waves.

Fig. 11.10: Reflection of sound

• Now, measure the angles of incidence and reflection and see the relationship between the
angles.

• Lift the pipe on the right vertically to a small height and observe what happens.

11.4 SPEED OF SOUND

Sound waves can be transmitted only by any medium containing particles that can vibrate. They
cannot pass through vacuum. However, the nature of the medium will affect the speed of the
sound waves. In general, the speed of sound in a liquid is five times that in gases; the speed of
sound in solid is about fifteen times that in gases.

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