# 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.

## Presentation on theme: "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."— Presentation 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 B QUANTUM 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=PL80C5AF53 6A5A90DF&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=PL80C5AF5 36A5A90DF Explination http://www.youtube.com/watch?v=N7BywkIretM&list=PL80C5AF536 A5A90DF Key Point The light has to have a sufficiently high frequency, called the cut off or threshold frequency, f 0.

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, V s, 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 E K(max) = E elec ½ mv 2 = eV s Where m is the mass of and electron e is the charge magnitude and V s 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, V s, 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, f 0.

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. E K(max) = hf = eV s 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 = hf 0 From, E = hf we can say… IB Equations hf = Φ + E K(max) hf = hf 0 + 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… eV s = hf – hf 0 y is eV s or E K(max) m is planck’s constnat or h b is hf 0 or Φ IB Definition h – planck’s constant Is 6.63 x 10 -34 Js

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