Question

If the wavelength of purple light is 400 x 10^-9 m, what is the frequency?

a) 7.5 x 10^14 /s
b) 8 X 10^14 Hz
c) 7.5 x 10^14 m
d) 8 x 10^14 m

Answer 1

The frequency : a) 7.5 x 10¹⁴ /s

Further explanation

Radiation energy is absorbed by photons

The energy in one photon can be formulated as

$\large{\boxed{\bold{E\:=\:h\:.\:f}}}$

Where

h = Planck's constant (6,626.10⁻³⁴ Js)

f = Frequency of electromagnetic waves  (/s or Hz)

f = c / λ

c = speed of light

= 3.10⁸  m/s

λ = wavelength

The wavelength(λ) of purple light is 400 x 10⁻⁹ m, so the frequency :

$\tt f=\dfrac{c}{\lambda}\\\\f=\dfrac{3.10^8~m/s}{4.10^{-7}m}\\\\f=\boxed{\bold{7.5.10^{14}}/s}$