Answer :
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
[tex]\large{\boxed{\bold{E\:=\:h\:.\:f}}}[/tex]
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 :
[tex]\tt f=\dfrac{c}{\lambda}\\\\f=\dfrac{3.10^8~m/s}{4.10^{-7}m}\\\\f=\boxed{\bold{7.5.10^{14}}/s}[/tex]
