Chapter 11

NCERT
Class 9
Science
Solutions
5. Flash and Thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen. Why?

Question:

Flash and Thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen. Why?

Answer:

Since, the speed of sound is much less than the speed of light. That is why thunder and flash are produced simultaneously. But thunder is heard a few seconds after the flash is seen.

Difference between Loudness and Intensity

Loudness Intensity
Loudness is the measure of the
sensitivity of the ear to sound which can
differentiate between loud and soft sounds.
The amount of sound energy passing
through a unit area in one second is
called the intensity of sound.
Loudness may be different for different
observers who depend on
the sensitivity of the
ears.
It does not depend on the
sensitivity of the ears.
It’s unit is decibel (dB). Its unit is watt/m2.

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