also know as topic:13 these notes were typed in association with physics for use with the ib diploma...

Also know as Topic:13

These 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 effect

13.1.2 – 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 effect

13.1.2 – 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.

• Demo

http://www.youtube.com/watch?v=WO38qVDGgqw&list=PL80C5AF536A5A90DF

• Explination

http://www.youtube.com/watch?v=N7BywkIretM&list=PL80C5AF536A5A90DF

Key Point

• The light has to have a sufficiently high frequency, called the cut off or threshold frequency, f0.

13.1.1 – Describe the photoelectric effect

13.1.2 – 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 this

Common Demo

• Occurs in a vacuum tube

13.1.1 – Describe the photoelectric effect

13.1.2 – 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 stopping

Potential, Vs, is adjusted until the

ammeter is zero.

• The stopping potential is the max

kinetic energy of the ejected

electrons.

13.1.1 – Describe the photoelectric effect

13.1.2 – 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 electron

e is the charge magnitude and

Vs is the stopping voltage.

13.1.1 – Describe the photoelectric effect

13.1.2 – 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 stopping

Potential, Vs, is adjusted until the

ammeter is zero.

• The stopping potential is the max

kinetic energy of the ejected

electrons.

13.1.1 – Describe the photoelectric effect

13.1.2 – 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 change

the energy of the electrons emitted.

13.1.1 – Describe the photoelectric effect

13.1.2 – 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 effect

13.1.2 – 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 = hf

Where 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 effect

13.1.2 – 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 effect

13.1.2 – 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