Question

Define work-function.

Hint:

Think of the work function as an "exit fee" for an electron leaving a metal. A photon's energy is the "payment." If the payment is less than the fee (\(E < \phi_0\)), the electron cannot leave. If it's exactly the fee (\(E = \phi_0\)), the electron leaves with no leftover energy (zero kinetic energy).

Answer 1

Step 1: Understanding the Concept:
The work function is a key concept in the study of the photoelectric effect. It represents the binding energy of the outermost (valence) electrons to the metal. To liberate an electron, this energy barrier must be overcome.

Step 2: Detailed Explanation:
\begin{itemize} \item Symbol and Units: The work function is typically denoted by \(\phi_0\) (phi-naught) or \(W\). It is a form of energy and is commonly measured in electron-volts (eV), although the SI unit is the joule (J).
\item Material Property: It is an intrinsic property of a specific material. Different metals have different work functions. For example, alkali metals like cesium have very low work functions, making them good materials for photoelectric devices.
\item Photoelectric Effect Context: In the photoelectric effect, if a photon with energy \(E = hf\) strikes the metal, an electron is emitted only if the photon's energy is greater than or equal to the work function (\(hf \geq \phi_0\)). The minimum frequency required is called the threshold frequency (\(f_0\)), where \(\phi_0 = hf_0\).
\end{itemize}

Step 3: Final Answer:
The work-function (\(\phi_0\)) is defined as the minimum energy that must be supplied to an electron to remove it from the surface of a given metal to a point just outside the metal with zero kinetic energy.