Question 191: Waves

Question

Two sitar strings,  A and B, playing the note 'Dha' are slightly out of tune and produce beats of frequency 5 Hz. The tension of the string B s slightly increased and the beat frequency is found to decrease by 3Hz. If the frequency of A is 425 Hz, the original frequency of B is :

Accepted Answer

Frequency of B, f
B
= 425 $$ \pm $$ 5 = 420 or 430 Hz
As tension of string  B  is increased
So, frequency of B, f
B
should also increase [as f $$ \propto $$ $$\sqrt T $$]
If initially f
B
= 430 Hz then when f
B
increases by increasing the tension then f
B
$$-$$ f
A
increases that means beat frequency increase.
So, f
B
can't be 430 Hz
When f
B
= 420 then when f
B
increases f
A
$$-$$ f
B
decreases means beat frequency decreases. So, correct f
B
= 420 Hz.

Answer

430 Hz

Answer

420 Hz

Answer

428 Hz

Answer

422 Hz

Waves

Two sitar strings, A and B, playing the note 'Dha' are slightly out of tune and produce beats of frequency 5 Hz. The tension of the string B s slightly increased and the beat frequency is found to decrease by 3Hz. If the frequency of A is 425 Hz, the original frequency of B is :

Choose the correct answer: