Physics Waves PMDC 2020
PMDC Verified Question 93 of 125
In a ripple tank, 40 waves pass through a certain point in 1 second. If the wavelength of the wave is 5cm. then speed of the wave is:
A
0.5 ms\(^{-1}\)
B
1 ms\(^{-1}\)
C
1.5 ms\(^{-1}\)
D
2 ms\(^{-1}\)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 2 ms\(^{-1}\)
Concept:

The wave equation links speed, frequency, and wavelength.

Formula:

$$ v = f \lambda $$

Solution:

  • The frequency (\( f \)) is simply the number of waves passing per second. So, \( f = 40 \text{ Hz} \).


  • The given wavelength is \( \lambda = 5 \text{ cm} \). To maintain standard SI units, convert this to meters: \( 5 \text{ cm} = 0.05 \text{ m} \).


  • Multiply them to find velocity: \( v = 40 \times 0.05 \).


  • \( v = 2 \text{ ms}^{-1} \).


Why other options are incorrect:

If a student forgets to convert centimeters to meters, they might incorrectly calculate \( 40 \times 5 = 200 \text{ cm/s} \), but the options are strictly in m/s.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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