Q. 74

Expert-verified
Found in: Page 454

### Physics for Scientists and Engineers: A Strategic Approach with Modern Physics

Book edition 4th
Author(s) Randall D. Knight
Pages 1240 pages
ISBN 9780133942651

# A physics professor demonstrates the Doppler effect by tying a 600 Hz sound generator to a 1.0-m-long rope and whirling it around her head in a horizontal circle at 100 rpm. What are the highest and lowest frequencies heard by a student in the classroom?

The maximum frequency is 619 Hz and the minimum frequency is 582 Hz

See the step by step solution

## Step 1: Write the given information

The frequency of the sound source is f = 600Hz

Length of the rope = 1 m

The rotation per minute of rope is 100

100 rpm= 1.66 rps (rotation per sec)

## Step 2: To determine the highest frequency of the sound source

The formula for the frequency heard by the listener when the source is moving is given by

Here,

f = frequency of the sound source

v = speed of the source

u = speed of the sound (340 m/sec)

The speed of sound of the generator is

Now substitute the known values in equation (1)

Thus, the maximum frequency heard by students is 619 Hz

## Step 3: To determine the minimum frequency heard by students

The formula for minimum frequency is

Now, substitute the known variables,

Thus, the minimum frequency heard by students is 582 Hz

The maximum frequency is 619 Hz and the minimum frequency is 582 Hz