Work Function

Definition of Work Function

Work function is defined as the minimum amount of energy required by an electron to escape from a metal surface.

Concept of Work Function in Classical Physics

The concept of work function is not to hard to understand. The concept can be explained by either classical physics or quantum mechanism. As per classical physics, when an electron tries to escape from metal surface, it leaves a positive image behind in the metal surface. Due attraction of this positive image negative electron turns back to metal surface hence cannot leave the metal crystal permanently. But to overcome this attraction force an electron requires sufficient energy supplied from outside normally from external light source.

The minimum energy requires to escape an electron form a metal surface is called work function.

Concept of Work Function in Quantum Physics

Work function can also be explained and defined by quantum physics. For that, we first have to know some basic features.
  1. Sir Albert Einstein said that light is in the form of a beam of a huge number of discrete energy packets called photons. The energy contains in each photon is hλ. Where, h is Planck Constant and λ is the frequency of light.
  2. Now when the light strikes on a metal surface electrons on the surface of the metal get energy from the light and get emitted from the surface. This is classically termed as photoemission.
  3. As the energy of photon Eph = hλ. The energy of each photon depends upon the frequency of light. As the frequency is everything upon which energy of photon rather light depends, it is found that there will be no photoemission from a metal surface below a certain frequency of light. For minimum photoemission frequency of incident light is required.
  4. If the frequency of light is higher than that above mention minimum rate for photoemission, then the extra energy of photon will be converted to Kinetic energy of the emitted electron. Hence, how fast the electron will be emitted from the surface of the metal depends upon the frequency of incident light. Not on the intensity (Brightness of the light).
  5. But when an intensity of incident light increases without changing its frequency. Obviously, number of photons strike on the metal surface hence more emitted electrons will be produced, but Kinetic energy of each electron will be unchanged as the frequency of incident light is fixed.
  6. Hence after a certain minimum frequency the electrons start emitted from a metal surface. Above this frequency, the Kinetic energy of the emitted electron is directly proportional to incident light frequency. But below this minimum frequency, there will be no Kinetic energy in the electrons.

Graphical Representation of Work Function

Now, If we graphically represent the above points we will get the graph below, work function Here, the vertical axis represents the energy of an electron and horizontal axis represents the frequency.

After frequency fo Hz, the Kinetic energy of electrons start increasing proportionally with frequency. Below, frequency fo or below energy hfo [ h is Planck Constant ] there will be no kinetic energy i.e. no emission of an electron. This amount of energy i.e. hfo is known and defined as work function λ.

Closely Related Articles Op-amp | Working Principle of Op-ampAmplifier Gain | Decibel or dB GainIntegrated Circuits | Types of ICRegulated Power SupplyLaser | Types and Components of LaserMobility of Charge CarrierWhat are Photo Electrons? Electron volt or eVEnergy Quanta | Development of Quantum Physics Schottky EffectHeisenberg Uncertainty PrincipleSchrodinger Wave Equation and Wave FunctionCyclotron Basic Construction and Working PrincipleSinusoidal Wave SignalCommon Emitter AmplifierRC Coupled AmplifierDifferential AmplifierWave Particle Duality PrincipleSpace ChargeInverting AmplifierMore Related Articles Vacuum Diode History Working Principle and Types of Vacuum DiodePN Junction Diode and its CharacteristicsDiode | Working and Types of DiodeDiode CharacteristicsHalf Wave Diode RectifierFull Wave Diode RectifierDiode Bridge RectifierWhat is Zener Diode?Application of Zener DiodeLED or Light Emitting DiodePIN Photodiode | Avalanche PhotodiodeTunnel Diode and its ApplicationsGUNN DiodeVaractor DiodeLaser DiodeSchottky DiodePower DiodesDiode ResistanceDiode Current EquationIdeal DiodeReverse Recovery Time of DiodeDiode TestingMOSFET | Working Principle of p-channel n-channel MOSFETMOSFET CircuitsMOS Capacitor | MOS Capacitance C V CurveApplications of MOSFETMOSFET as a SwitchMOSFET CharacteristicsPower MOSFETHalf Wave RectifiersFull Wave RectifiersBridge RectifiersClamping CircuitTheory of SemiconductorIntrinsic SemiconductorExtrinsic SemiconductorsEnergy Bands of SiliconDonor and Acceptor Impurities in Semiconductor Conductivity of SemiconductorCurrent Density in Metal and Semiconductor Intrinsic Silicon and Extrinsic SiliconP Type SemiconductorN Type SemiconductorP N Junction Theory Behind P N JunctionForward and Reverse Bias of P N JunctionZener BreakdownAvalanche BreakdownHall Effect Applications of Hall EffectGallium Arsenide SemiconductorSilicon SemiconductorTypes of TransistorsBipolar Junction Transistor or BJTBiasing of Bipolar Junction Transistor or BJTTransistor BiasingTransistor CharacteristicsCurrent Components in a TransistorTransistor Manufacturing TechniquesApplications of Bipolar Junction Transistor or BJT | History of BJTTransistor as a SwitchTransistor as an AmplifierJFET or Junction Field Effect Transistorn-channel JFET and p-channel JFETApplications of Field Effect TransistorDIAC Construction Operation and Applications of DIACTRIAC Construction Operation and Applications of TRIACPhototransistorNew Articles Ring CounterDischarging a CapacitorCharging a CapacitorElectric PotentialParity GeneratorElectric Flux