Also know as Topic:13These notes were typed in association with Physics for use with the IB Diploma Programme by Michael Dickinson

For further reading and explanation see:Physics, Tsokos (purple): Ch 6.4 Physics, Giancoli (mountain): Ch 27

OPTION BQUANTUM AND NUCLEAR PHYSICS

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• Frist off lets get a quick summary of everything. Try this link.

http://www.youtube.com/watch?v=WaZdgrwm2dw&list=PL80C5AF536A5A90DF&index=1

• So that’s were we are going.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• Things and get a little tricky so hang on and review often. • Photoelectric Effect - When light shines on a clean metal surface, electrons

are emitted from the surface.• Demohttp://www.youtube.com/watch?v=WO38qVDGgqw&list=PL80C5AF536A5A90DF• Explinationhttp://www.youtube.com/watch?v=N7BywkIretM&list=PL80C5AF536A5A90DFKey Point• The light has to have a sufficiently high frequency, called the cut off or

threshold frequency, f0.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• Cathode – negatively charged electrode, electrons flow away from this• Anode – positively charged electrode, electrons flow toward thisCommon Demo• Occurs in a vacuum tube

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• Millikan’s Experiment• Applies a variable potential difference across the electrodes. This

produces an opposing electric field to the movement of the ejected electrons. • The reverse potential, or stoppingPotential, Vs, is adjusted until the

ammeter is zero. • The stopping potential is the maxkinetic energy of the ejected electrons.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• Millikan’s Experiment• EK(max) = Eelec

• ½ mv2 = eVs

• Where m is the mass of and electrone is the charge magnitude and Vs is the stopping voltage.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• Millikan’s Experiment• Applies a variable potential difference across the electrodes. This

produces an opposing electric field to the movement of the ejected electrons. • The reverse potential, or stoppingPotential, Vs, is adjusted until the

ammeter is zero. • The stopping potential is the maxkinetic energy of the ejected electrons.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.Frequency vs. max kinetic energy graph• Increase the frequency of the light shining on the metal, there is an

increase in kinetic energy of the ejected electrons. • The intensity of the incident light is proportional to the number of

electron emitted. But also an increase in intensity didn’t changethe energy of the electrons emitted.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.Millikan’s Experiment• Why did the metal not emit electrons immediately, but did so after a

certain frequency. • The light has to have a sufficiently high frequency, called the cut off or

threshold frequency, f0.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• Einstein continued Max Planck’s work and developed the particle theory. • Planck observed that energy released from vibrating molecules were

always in packets called quanta of energy. • Einstein said that light originates from a vibrating source then light energy

could be quantized particles called photons.• Each with an energy of E = hfWhere E is energy, h is Planck’s constant, f is frequency.• With this theory everything started to fall in place.• EK(max) = hf = eVs

• Increasing the intensity of light at constant frequency means a greater quantity of electrons would be ejected, but does not increase the energy of each photon and so does not increase the max kinetic energy of the ejected electron.

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• At low frequencies the photon energy is low and electrons are not

emitted.• Work Function Φ – the minimum amount of energy of photons

incident on a surface required to cause photoelectric emission.• Φ = hf0 • From, E = hf we can say…IB Equations• hf = Φ + EK(max)

• hf = hf0 + eV

13.1.1 – Describe the photoelectric effect13.1.2 – Describe the concept of the photon, and use it to explain the photoelectric effect.13.1.3 – Describe and explain an experiment to test the Einstein model.• All this can be arranged in y = mx + b form…• eVs = hf – hf0

• y is eVs or EK(max)

• m is planck’s constnat or h• b is hf0 or Φ

IB Definition• h – planck’s constant• Is 6.63 x 10-34 Js