Two tuning forks of frequencies 6Hz and 4Hz respectively are sounded together. The beat frequency is

Analyze the question Two tuning forks with frequencies 6 Hz and 4 Hz are sounded together. We need the beat frequency.

Concept When two sound waves of slightly different frequencies are sounded together, they interfere and produce a periodic rise and fall in loudness called beats. The beat frequency is the difference between the two frequencies:

f_beat = |f₁ − f₂|

Solution

• f₁ = 6 Hz
• f₂ = 4 Hz

f_beat = |6 − 4| = 2 Hz

This means you would hear 2 loud sounds (beats) every second.

Checking the other options

• 5 Hz is the average of the frequencies (6 + 4)/2, not the beat frequency.
• 10 Hz is the sum (6 + 4), which is not the beat frequency.
• 8 Hz does not come from any correct relationship between the two frequencies.

Exam tip Remember: beats = difference. Subtract the smaller frequency from the larger. Students often add the frequencies by mistake, so if you see "beat frequency" in a question, think "subtract."