Test: Reflection of Waves & Beats (September 29) - NEET MCQ

In a plane mirror, angle of incidence i = angle of reflection r.
The angle between the incident and reflected rays is i + r = 2i
Given 2i = 60^∘
⇒ i = 30^∘

To find the frequency of the beats produced when two sounds with frequencies of 256 Hz and 260 Hz are combined, we can use the following method:

• Calculate the difference between the two frequencies: 260 Hz - 256 Hz = 4 Hz
• The frequency of the beats is equal to this difference.

Therefore, the frequency of the beats is 4 Hz.

Let the unknown frequency be f.
With fork A:

Beat frequency = ∣f−258∣  

With fork B:

Beat frequency = ∣f−262∣

Given that the beat frequency with B is double that with A,

∣f−262∣ = 2 ∣f−258∣

Assume f < 258 (since doubling occurs when the note is on the lower side):

So, Option (c) is the correct answer.

When two sound waves with slightly different frequencies travel in the same direction, they create a phenomenon known as beats. This occurs due to the interference of the sound waves. Here’s a simplified explanation of the process:

• As the waves move, they occasionally reinforce each other, resulting in a louder sound.
• At other times, they can cancel each other out, leading to a softer sound.
• This pattern of alternating loud and soft sounds is perceived as beats.

In summary, the interaction of the two sound waves through interference is what produces the effect known as beats.