The bells of a temple are made of large size. It is for

State whether the following statement is true or false: Sound waves are transverse,whereas light waves are longitudinal in nature.

Mention one practical use of echoes.

$(a)$ Briefly mention three uses of ultrasound in the field of medicine.
$(b)$ $A$ ship which is stationary is at a distance of $2800 \ m$ from the sea-bed. The ship sends an ultrasound signal to the sea-bed and its echo is heard after $4 \ s$. Find the speed of sound in water.

$(a)$ Illustrate the use of a stethoscope.
$(b)$ What are infrasonic and ultrasonic sound waves?

$(a)$ Which of the following frequencies are audible to human ears: $2 \, Hz$,$5 \, Hz$,$20 \, Hz$,$200 \, Hz$,$2000 \, Hz$?
$(b)$ How are moths of certain families able to escape capture?