Please help! I dont understand.

Question

What is the wavelength (in nm) of a photon if the energy is 7.61 × 10⁻¹⁹ J? (h = 6.626 × 10⁻³⁴ J • s)

Answer 1

For these problems, you need to memorize/learn a few equations.

E = energy (usually in joules)

h = Planks constant = 6.626x10^-34 Js

c = speed of light = 3x10⁸ m/s

λ = wavelength (usually in meters)

ν = frequency (in Hz = sec^-1)

E = hν

c= λν

E = hc/λ

In this problem, we are given E (energy) and asked to find wavelength (λ)

Use E = hc/λ

7.61x10^-19 J = (6.626x10^-34 Js)(3x10⁸ m/s) / λ

Solving for λ (wavelength), we have ...

λ = (6.626x10^-34 Js)(3x10⁸ m/s) / 7.61x10^-19 J

λ = 2.61x10-7 m (note the units are in meters)

To convert this to nanometers (nm), we do the following conversion:

2.61x10^-7 m x 1x10⁹ nm / m = 261 nm