# NCERT Physics Class 11 Exemplar Ch 15 Waves Part 5

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32. The earth has a radius of 6400 km. The inner core of 1000 km radius is solid. Outside it, there is a region from 1000 km to a radius of 3500 km which is in molten state. Then again from 3500 km to 6400 km the earth is solid. Only longitudinal (P) waves can travel inside a liquid. Assume that the P wave has a speed of 8 km in solid parts and of 5 km in liquid parts of the earth. An earthquake occurs at some place close to the surface of the earth. Calculate the time after which it will be recorded in a seismometer at a diametrically opposite point on the earth if wave travels along diameter?

Ans:

33. If c is R.M.S. speed of molecules in a gas and v is the speed of sound waves in the gas, show that c/v is constant and independent of temperature for all diatomic gases.

Ans:

for diatomic gases.

34. Given below are some functions of x and t to represent the displacement of an elastic wave.

(a)

(b)

(c)

(d)

State which of these represent

(a) A travelling wave along direction

(b) A stationary wave

(c) Beats

(d) A travelling wave along direction.

Ans:

(a) (ii),

(b) (iv),

(c) (iii),

(d) (i).

35. In the given progressive wave

Where y and x are in m, t is in s. What is the

(a) Amplitude

(b) Wave length

(c) Frequency

(d) Wave velocity

(e) Particle velocity amplitude.

Ans:

(a)

(b)

(c)

(d)

(e) .

36. For the harmonic travelling wave where x and y are in cm and t is second. What is the phase difference between the oscillatory motions at two points separated by a distance of?

(a) 4 m

(b)

(c)

(d) (at a given instant of time)

(e) What is the phase difference between the oscillation of a particle located at at and?

Ans: