Question

What is the energy of a photon of light having a wavelength of 4.5 x 10-7 meters? (Planck’s constant is 6.626 x 10-34 joule seconds; the speed of light is 2.998 x 108 m/s)
2.9817 x 10-40 joules



4.4143 x 10-19 joules



6.6745 x 10-26 joules second



9.9456 x 10-49 joules



19.864 x 10-26 joules/second

Answer 1

The answer is 4.4143 x 10-19 joules

The energy (E) is: E = h * f
h - Planck's constant
f - the frequency

The frequency (f) is: f = c/∧
c - the speed of light
∧ - the wavelength

Hence:
E = h * f = h * c / ∧

We know:
h = 6.626 x 10⁻³⁴ Js
c = 2.998 x 10⁸ m/s
∧ = 4.5 x 10⁻⁷ m

E = 6.626 x 10⁻³⁴ Js * 2.998 x 10⁸ m/s / 4.5 x 10⁻⁷ m 
E = 4.4143 x 10⁻³⁴ ⁺ ⁸ ⁻ ⁽⁻⁷⁾ J 
E = 4.4143 x 10⁻¹⁹ J