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