What is the range of audible frequencies for a normal human ear? 

17 What frequencies are heard and produced by dogs and bats respectively? 18 Pendulum A makes 14 oscillations in five seconds and pendulum B makes 10 oscillations in three seconds. Which has a higher frequency? Express the frequency of each pendulum in hertz. 20 Give two applications of ultrasound in medical sciences. 21 Give two applications of ultrasound in industries.