# NCERT Class 11 Physics Solutions: Chapter 15 – Waves-Part 3

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**Question 15.5:**

You have learnt that a travelling wave in one dimension is represented by a function where must appear in the combination i.e. Is the converse true? Examine if the following functions for y can possibly represent a travelling wave:

**Answer: No;**

: Does not represent a wave

The converse of the given statement is not true. The essential requirement for a function to represent a travelling wave is that it should remain finite for all values of

**Explanation:**

For the function becomes

Hence, for , the function represents a point and not a wave.

: Represents a wave

**Explanation:**

For the function

Since the function does not converge to a finite value for, it represents a travelling wave.

: Does not represent a wave

**Explanation:**

For, the function

Since the function does not converge to a finite value for , it does no represent a travelling wave.

**Question 15.6:**

A bat emits ultrasonic sound of frequency in air. If the sound meets a water surface, what is the wavelength of,

The reflected sound,

The transmitted sound?

Speed of sound in air is

**Answer:**

Frequency of the ultrasonic sound,

Speed of sound in air,

The wavelength of the reflected sound is given by the relation:

Frequency of the ultrasonic sound,

Speed of sound in water,

The wavelength of the transmitted sound is given as: