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JAMB Physics 2015 Paper

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Question : 41

Total: 66

A radioactive source emits X–rays of very short wavelength (10 -13m ). what is the frequency of these rays?

2 × 10¹⁸HZ
3 × 10 ¹⁹HZ
3 × 10²¹HZ
3 × 10^-19HZ

Solution:

Concept:

Electromagnetic waves travel at the speed of light, so frequency is found using

c = f\lambda

.

Explanation:

Given wavelength,

\lambda = 10^{-13}\,\text{m}

.

Speed of X-rays,

c = 3 \times 10^{8}\,\text{m/s}

.

Frequency,

f = \frac{c}{\lambda}

.

Substitute the values:

f = \frac{3 \times 10^{8}}{10^{-13}}

.

Using the law of indices,

f = 3 \times 10^{8} \times 10^{13}

.

Therefore,

f = 3 \times 10^{21}\,\text{Hz}

.

Answer:

The frequency of the X-rays is

3 \times 10^{21}\,\text{Hz}

.

Correct option: C.

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