Unit 3: Topic 12 - Photoelectric Effect

Question 1

Describe the photoelectric effect

Answer 1

The photoelectric effect is a phenomenon where charged particles release from some material when hit by electromagnetic radiation. A photon will release energy equivalent to hv, where h is Planck’s constant, and v is the frequency of the photon. Einstein and experiments around the early 1900s showed that the energy of the photon decreases by some work functionΩ so that E = hv - Ω.

Question 2

Describe the diagram of the electromagnetic spectrum, and use it to rank all of the wavelengths from smallest to largest.

Answer 2

Electromagnetic Spectrum. From smallest to largest wavelength, we have gamma, x-ray, ultraviolet, visible (from violet to red), infrared, microwave, and radio wave: a way to memorize is to see that U-violet goes to violet, red to infrared

Question 3

Calculate the energy emitted by an ultraviolet particle with a wavelength of 300nm.

Answer 3

We will use the formulas c = λν and E = hv so that E = hv = hc/λ. Since h is given by Planck’s constant 6.626 * 10^-34 J Hz^-1 and c is the speed of light 3 * 10^8 m/s, then E = (6.626 * 10^-34 s J) * (3 * 10^8 m/s)/(300 * 10^-9 m). = 6.626 * 10^-19 J, which is reasonable (one proton is 1.602 * 10-^19 J). Dimensional Analysis