Threshold frequency & wavelength
Threshold frequency
- The threshold frequency is defined as:
The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal
Threshold wavelength
- The threshold wavelength, related to threshold frequency by the wave equation, is defined as:
The longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal
- Threshold frequency and wavelength are properties of a material and vary from metal to metal
Threshold frequencies and wavelengths for different metals
Metal | Threshold Frequency (f0) / Hz | Threshold Wavelength (λ0) / nm |
Sodium | 4.40 × 1014 | 682 |
Potassium | 5.56 × 1014 | 540 |
Zinc | 1.02 × 1015 | 294 |
Iron | 1.04 × 1015 | 289 |
Copper | 1.13 × 1015 | 266 |
Gold | 1.23 × 1015 | 244 |
Silver | 9.71 × 1015 | 30.9 |
Examiner Tip
A useful analogy for threshold frequency is a fairground coconut shy:
- One person is throwing table tennis balls at the coconuts, and another person has a pistol
- No matter how many of the table tennis balls are thrown at the coconut it will still stay firmly in place – this represents the low frequency quanta
- However, a single shot from the pistol will knock off the coconut immediately – this represents the high frequency quanta