MCQ practice · SSC Physics Board questions · Chapter 7: Waves and Sound
Which relation is correct?
Think it through first, then pick an option.
- a Fs = −Kx
- b 1/u + 1/f = 1/v
- c T = 2π√(g/l)
- d f = vλ
Answer and explanation
Correct answer: a Fs = −Kx
By Hooke's law the restoring force of a spring is F = −kx; the minus sign shows the force points opposite to the displacement.
Why the other options are wrong
- b 1/u + 1/f = 1/v: This relation is not from this chapter and is not correct in this form. One of this chapter's formulas is F = −kx.
- c T = 2π√(g/l): The pendulum formula is T = 2π√(l/g); here g and l are the wrong way round.
- d f = vλ: The wave formula is v = fλ; here f = vλ is written, which is not right. The correct form is f = v/λ.
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