Question

A certain color of light towards the purple end of the visible spectrum has a wave length of $420nm$ in vacuum.
What is the frequency of this light? (The speed of light in a vacuum is $3.00\times {10}^{8}m/s$).

• A. $126Hz$
• B. $1.26\times {10}^{11}Hz$
• C. $7.1\times {10}^{14}Hz$
• D. $1.4\times {10}^{15}Hz$
• E. $1.4\times {10}^{6}Hz$

Answer 1

The correct option is C $7.1\times {10}^{14}Hz$

Wavelength of the light $\lambda =420$ nm $=420\times {10}^{-9}$ m

Speed of light $v=3.00\times {10}^8$ m/s

Thus frequency of the light $\nu =\frac{v}{\lambda }=\frac{3.00\times {10}^8}{420\times {10}^{-9}}=7.14\times {10}^{14}$ $Hz$