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JAMB Physics 2019 Paper

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Question : 25

Total: 100

A vibrator causes water ripples to travel across the surface of a tank. The wave travels 50cm in 2s and the distance between successive crests is 5cm. Calculate the frequency of the vibrator

5Hz
6Hz
5.2Hz
25Hz

Solution:

Concept:

Wave speed is found from distance and time, then frequency is calculated using the wave equation.

Explanation:

The wave travels

50\,\text{cm}

in

2\,\text{s}

.

So, speed

v = \frac{50\,\text{cm}}{2\,\text{s}} = 25\,\text{cm/s}

.

Distance between successive crests is the wavelength:

\lambda = 5\,\text{cm}

.

Using the wave equation

v = f\lambda

:

f = \frac{v}{\lambda} = \frac{25\,\text{cm/s}}{5\,\text{cm}} = 5\,\text{Hz}

.

Answer:

5\,\text{Hz}

— Option A.

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