Threshold Frequency and Work Function

• What is the photoelectric effect?

  Electrons emitted from metal by light

  
• What are electrons emitted from a metal called?

  Photoelectrons

  
• What does the photoelectric effect demonstrate about light?

  Light behaves as a particle

  
• What does it mean that light is quantized?

  Light is carried in discrete packets
• What is the significance of the threshold frequency?

  Only frequencies above it emit photoelectrons
• How is the threshold frequency defined?

  Minimum frequency to remove a photoelectron
• What is the threshold wavelength?

  Longest wavelength to remove a photoelectron
• How are frequency and wavelength related?

  By the wave equation

  
• What varies from metal to metal regarding the photoelectric effect?

  Threshold frequencies and wavelengths

  
• What is the work function Φ?

  Minimum energy to release a photoelectron
• How can the work function be visualized?

  As energy between surface and top of well
• What happens when an electron absorbs a photon with energy equal to Φ?

  It can escape from the metal surface
• How do different metals affect threshold frequencies?

  They have different attractive forces

  
• Which metals have threshold frequencies in the visible light region?

  Alkali metals like sodium and potassium

  
• Which metals have threshold frequencies in the ultraviolet region?

  Transition metals like zinc and iron

  
• What is stopping potential V?

  Potential difference to stop photoelectron emission
• What happens to photoelectrons in the setup with emitter and collector plates?

  Electrons are collected at the collector plate

  
• What does the flow of electrons create in the circuit?

  Electromotive force (e.m.f.)
• What happens when the e.m.f. is increased?

  Emitter plate becomes more positive
• What does the potential difference across the tube do?

  Opposes the motion of electrons
• What is the stopping potential V at maximum kinetic energy?

  Energy needed to cross the gap
• What is the equation for maximum kinetic energy of photoelectrons?

  Ek max = eVs
• What does increasing intensity of radiation do?

  Increases number of emitted photoelectrons
• What remains constant when intensity increases?

  Stopping potential
• What affects the maximum kinetic energy of photoelectrons?

  Frequency and work function of the metal
• What happens when frequency increases while keeping intensity constant?

  Photoelectric current decreases
• Why does photoelectric current decrease with increased frequency?

  Fewer photons emitted per unit area
• What does the stopping potential indicate?

  Maximum kinetic energy of emitted electrons
• What is important about the sign of stopping voltage?

  Its sign is not important in calculations