Write Einstein's photoelectric equation. Use it to explain the laws of photoelectric emission, and show how Planck's constant and the work function can be found from a graph.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Write the equation. K_max = hν − φ₀, or eV₀ = hν − φ₀.
2 · State the photon idea. Light is made of photons of energy hν; one photon is absorbed by one electron.
3 · Explain the threshold frequency. Emission needs hν ≥ φ₀, so ν₀ = φ₀/h.
4 · Explain the effect of intensity. Intensity is the number of photons per second; it changes the current, not K_max.
5 · Explain why there is no time lag. The photon's energy is given in one packet, so emission is instantaneous.
6 · Draw the V₀ against ν graph. [Straight line starting at ν₀ on the ν axis; slope h/e; dashed extension to −φ₀/e on the V₀ axis]
7 · Find h and φ₀. h = e × slope; φ₀ = hν₀, or e times the size of the intercept on the V₀ axis.
8 · Close in one line. So, Einstein's equation shows the particle nature of light.
Scoring tip: Write both forms of the equation and name every symbol; then explain each law in one line.
