'Beats' is a phenomenon that occurs when frequencies of two harmonic waves are
- (a)equal.
- (b)far apart.
- (c)multiples of each other.
- (d)nearly same.
Correct — D, nearly same. Beats are the periodic rise and fall in loudness heard when two sound waves of slightly different frequencies are sounded together. As the two waves drift in and out of phase, they alternately reinforce and cancel, so the loudness waxes and wanes at a rate equal to the difference of the two frequencies (beat frequency = |f₁ − f₂|). This regular throbbing is audible only when the frequencies are close — that is, nearly the same.
- (a)equal. — If the two frequencies were exactly equal the difference would be zero, giving no waxing and waning at all — just a steady tone, not beats.
- (b)far apart. — When the frequencies are far apart the beat frequency is very high; the loudness variations become too rapid to perceive as distinct beats and are heard instead as dissonance.
- (c)multiples of each other. — Frequencies that are multiples (harmonics) of one another blend into a musically consonant, steady sound; they do not produce the slow throb characteristic of beats.
Beats arise from the superposition (interference) of two waves of slightly different frequency travelling in the same direction. Their combined amplitude is modulated slowly in time, so the listener hears the sound grow loud and soft repeatedly. The number of beats heard per second equals the difference between the two source frequencies.
The clue is the word 'nearly'. Beats depend on a small frequency mismatch: too small (equal) and nothing changes; too large (far apart) and the effect is inaudible. Musicians use this when tuning — two strings are in tune when the beats slow to zero.
- Beat frequency = |f₁ − f₂|, the difference of the two source frequencies.
- Beats result from superposition (interference) of two waves of nearly equal frequency.
- They are heard as a periodic swelling and fading of loudness.
- Instrument tuning uses beats: identical frequencies give zero beats.
- Choosing 'equal' — equal frequencies give a steady tone (zero beats), not beats.
- Assuming any two frequencies beat; the difference must be small enough to hear.
Asked as the condition for beats, or as a numerical 'how many beats per second' from two given frequencies.
No directly related past PYQ was found.
- practice — not a real PYQ
Two tuning forks of frequencies 256 Hz and 260 Hz are sounded together. The number of beats heard per second is
- (a)2
- (b)4
- (c)8
- (d)516
Answer(b) 4 — beat frequency = |260 − 256| = 4 per second.
- practice — not a real PYQ
Beats are a result of which wave phenomenon?
- (a)Reflection
- (b)Refraction
- (c)Superposition (interference)
- (d)Dispersion
Answer(c) Superposition (interference) — of two waves of nearly equal frequency.