TOPIC 5: PARTICLE NATURE OF LIGHT

What is a photon

A small packet of energy

What is wave particle duality

The idea that electrons can act as both a wave and a particle

Define wave phenomen

all the things that only waves can do

What are the 4 types of wave phenomena

Reflection,Refraction,Diffraction interference

What is planks constant

6.63x10-34

What two phenomena prove that Waves act as a particle

The photoelectric effect
Line spectra

What is planks constant theory

The idea that electromagnetic radiation is emitted is very small and the higher the frequency the higher the energy

What is the derivation for planks constant

E=∝f
E=kf
E=hf

What is work function

The minimum amount of energy required to release one electron from its ionic lattice in a metal

What is the threshold frequency

when the work function is equal to the photon energy

What is the equation for The energy of a photon

E=hf

What is the photoelectric equation

Hf=Φ +ke

What is the de broglie wavelength

λ=h/mv

define de broglie wavelength

Any particle with a momentum has an associated wavelength

Define the stopping potential

The work done against the electrons to cancel out the Kinetic energy

What is the exitation energy

The amount of energy required for an electron to escape from the surface of a metal

What is the ionisation energy

The amount of energy an electron needs to ionise and break free from its lattice

What is the photoelectric effect

Proof that light has a particle nature

Why is the wave theory for the photoelectric effect incorrect

Wave theory states that the longer the light is shone on the metal the more energy it has

Eventually low intensity light will still release enough electrons as it will build up energy

Explain the photoelectric effect

Electrons trapped in ionic lattice of metal due to positive charge

Electrons get energy from light waves in order to ionise and escape the metal

Once the electrons escape any residual energy is converted into kinetic energy as it it leaves the metal
Which need less energy to escape electrons closer to the top of the metal or the middle Top

How many experimental findings are their for the photoelectric effect?

3

How do you convert from EV to J

/ 1.6x10-19

How do you convert from J to EV

x 1.6 x10-19

What is the gradient on a photoelectric graph

Planks constant

What is the y intercept on a photoelectric graph

Work function

what is the X axis on a photoelectric graph

Frequency

what is the Y axis on a photoelectric graph

Kinetic energy

What is the point at which the Kinetic energy is 0 on the graph

The fundamental frequency

What is the equation for stopping potential

work done =kinetic energy
VQ=1/2MV^2

What can the stopping distance be used for (3)

helps to find the kinetic energy of something small as e-
Can vary frequency & see how it affects KE
find the threshold frequency and work done

What is a photo vacuum cell

A component containing a photocathode and an anode that can produce photoelectrons.

Explain how a photo vacuum cell works with a cell to generate a stopping potential

When a cell is added to produce a voltage in the opposite direction to the flow of the photoelectrons. When this voltage is high enough it can be used to stop the flow of photoelectrons. this us the stopping potential which we can use to measure the amount of photoelectrons we have in a a current.