# 5 - Standing waves Questions Answers

how can we calculate ratio of intensities of two sound waves  having unequal amplitudes (one having double the amplitude of the other - both are sinusodial waves) and the graph is displacement vs time .

Joshi sir comment

Intensity of a wave depends on two power of amplitude and two power of frequency. Check the graph carefully for getting idea about frequency and details of amplitude are given in the question.

in a stationery wave, there is no energy current, but there is energy density. (TRUE/FALSE)

Joshi sir comment

TRUE

at STP, the speed of sound in hydrogen is 1324ms‾¹ then the spped of sound in air (at STP) is

Joshi sir comment

formula for speed of sound is v = √(γRT/M)

you have to form two equations for the two mediums, for both the mediums γ will be same because Hydrogen and Air both are diatomic gases, T will also be same for both the cases are taken in STP, only M will be different

a person is standing between two vertical walls. he heard the echo of his sound after t = 1s and t = 1.5s. distance between walls is (speed of sound in air = 340ms‾¹

Joshi sir comment

time taken by the sound to reach upto the first wall = 0.5 sec

similarly time taken by the sound to reach upto the second wall = 0.75

so total time = 1.25 sec. so distance between the walls = 340 * 1.25 = 425

which of the following is minimum audible wavelength at room temperature?

(1) 20mm

(2) 20cm

(3)20m

(4) 20km

Joshi sir comment

maximum audible frequency = 20000 Hz

Velocity of sound = 340 m/s

so minimum audible wavelength = 340/20000 m = 34000/20000 cm = 340/20 mm = 17 mm approx 20 mm