| English | Threshold frequency |
|---|---|
| Bahasa Melayu | Frekuensi ambang |
| 中文 | 极限频率 |
Definition
The minimum frequency of light needed to cause the emission of electrons from a particular metal surface.
In exam terms
The threshold frequency is the minimum frequency of light needed to cause the emission of electrons from a particular metal surface. Its symbol is f₀ and it is measured in hertz (Hz).
Below it, no electrons are emitted no matter how bright the light.
It links to the work function by f₀ = W / h, where W is the work function and h is Planck's constant. A correct exam line: f₀ = W / h = (3.3 × 10⁻¹⁹ J) ÷ (6.63 × 10⁻³⁴ J s) = 5.0 × 10¹⁴ Hz. At exactly f₀, an electron is just freed with zero kinetic energy.
Do not confuse it with…
Do not confuse the threshold frequency with the work function. The threshold frequency is a frequency (in Hz); the work function is an energy (in J).
They are linked by W = hf₀, so a metal with a larger work function has a higher threshold frequency.
In Paper 2 this is asked as define the threshold frequency, or determine it from the intercept of an energy–frequency graph. When defining, always include 'minimum frequency' and 'for a particular metal', a metal with a different work function has a different f₀, and always give the unit as Hz.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)