Question

A light wave has a wavelength of 1.5E-7m. The speed of light is 3E8m/s. Planck's constant is 6.6E-34 m²kg/s.

c=wavelength*frequency
Energy-=h*frequency
a. What is it's frequency?
b. What is it's energy?

Answer 1

The Energy is 1.35 x 10^-18 kgm^2/s^2 (or Joules) for the photon with wavelength 1.5x10^-7 m.

Step-by-step explanation:

We are given the two relationships needed to answer the questions:

• Energy = (Planck's Constant)*(Frequency), and
• Speed of Light (3.0x10^8 m/s) = Wavelength*Frequency

Lets determine the light wave's frequency first, since that is what is requested in the equation for energy.

Speed of Light = Wavelength*Frequency

3.0x10^8 m/s = (1.5x10^-7 m)*Frequency

Frequency = (3.0x10^8 m/s)/(1.5x10^-7 m)

Frequency = 2.0x10^15/s (Hz)

Now we can calculate energy:

Energy = (Planck's Constant)*(Frequency)

Energy = (6.6x10^-34 m^2kg/s)*(2.0x10^15/s)

Energy = 1.35 x 10^-18 kgm^2/s^2

The unit "kg*m^2/s^2" is known as a Joule

So we can also say that the energy is 1.35 x 10^-10 Joules