What is meant by the dual nature of radiation? Define work function and describe the ways in which electrons can be emitted from a metal surface.

1. 1 · Dual nature in one line. Light behaves as a wave in interference and diffraction, and as particles (photons) in the photoelectric effect.
2. 2 · Define work function. The minimum energy for an electron to escape the metal surface; it depends on the metal and its surface; unit eV.
3. 3 · Define the electron volt. 1 eV = 1.6 × 10⁻¹⁹ J.
4. 4 · List the ways.
   • Thermionic emission: by heat
   • Field emission: by a very strong electric field
   • Photoelectric emission: by light of suitable frequency
5. 5 · Real life. Solar panels and phone light sensors use the particle nature of light.
6. 6 · Close in one line. So, both the wave and the particle pictures are needed to describe light.

Scoring tip: Always give the unit of work function (eV) and the conversion 1 eV = 1.6 × 10⁻¹⁹ J.