21.
The minimum distance between the source and the reflector, so that an echo is heard is approximately
A
12 m
B
15 m
C
17 m
D
21 m
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The minimum distance between the source and the reflector, so that an echo is heard is approximately
12 m
15 m
17 m
21 m
Bats detect the obstacles in their path by receiving the reflected ______.
radio waves
ultrasonic waves
electromagnetic waves
infrasonic waves
When a wave travels through a medium ______.
energy is transferred at a constant speed
energy is transferred in a periodic manner
particles are transferred from one place to another
none of these