Physics · Dual Nature Of Radiation And Matter · NEET
Metals conduct because they have free electrons that move around inside. But if one electron tries to leave the surface, the metal is left slightly positive, so it pulls the electron straight back. This attractive pull acts like an invisible wall at the surface. An electron can escape only if it is given extra energy to overcome this pull.
The work function is the minimum energy needed to pull one electron out of the metal surface. It is written as phi-zero and measured in eV (electron volt). 1 eV = 1.6 x 10^-19 J. A larger work function means the metal holds its electrons more tightly, so more energy is needed to free them.
No. Ionisation energy is the energy to remove an electron from a single free atom in the gas state. Work function is the energy to remove an electron from the surface of a solid metal, where many atoms and free electrons act together. They are related ideas but different quantities, and for the same element they are usually not equal.
No. The work function is a fixed property of the metal itself (and its surface condition). Shining brighter or different-coloured light does not change phi-zero. The light only supplies energy; whether an electron escapes depends on comparing that supplied energy with the fixed work function.
The work function is the 'cost' paid just to get out of the metal. Any energy given to the electron above the work function becomes its kinetic energy after it escapes. So supplied energy = work function + kinetic energy. If the supplied energy only equals the work function, the electron just barely escapes with almost zero speed.
The work functions of Caesium (Cs), Potassium (K) and Sodium (Na) are 2.14 eV, 2.30 eV and 2.75 eV respectively. If incident electromagnetic radiation has an energy of 2.20 eV, which of these photosensitive surfaces emit electrons?
The work function of a photosensitive material is 4.0 eV. The longest wavelength of light that can cause photoemission from the substance is (approximately):
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Electron emission is the process of freeing electrons from the surface of a metal by giving them enough energy to escape the metal's attractive pull.
Work function is usually measured in electron volt (eV). It can also be written in joule, where 1 eV = 1.6 x 10^-19 J.
The work function is written as phi-zero. A larger phi-zero means electrons are held more tightly inside the metal.
No. Heating a metal supplies energy to the electrons so some can escape (thermionic emission), but it does not change the metal's work function value itself.
Alkali metals like caesium, potassium and sodium have low work functions, which is why they emit electrons easily even with visible or ultraviolet light. Caesium has the lowest among these three.
