Photoelectricity, X-rays & LASER (2020_07_05 05_21_37 UTC).pptx

Photoelectricity, X-rays & LASER

1. Photo electricity Presentation by: Mr. Pawar B N X- rays LASER

2. Photo electricity Photo (Light Energy) Electricity (Electrical Energy) Light energy is converted into electrical energy

3. Photoelectric Effect When light of suitable frequency is incident on metal surface, electrons are emitted from the surface. This effect is called as Photoelectric effect . Electrons thus emitted are called Photo electrons. And current so produced is known as Photoelectric current.

4. Photoelectric Effect

5. Planck’s Hypothesis Point 1 Energy is always absorbed or emitted in discrete packets. Point 2 Each energy packet is called ‘Photon’ or quanta. Point 3 Energy of each photon is E = hf . Energy is proportional to frequency . Point 4 In absorption atom gains energy In emission atom loses energy (Photon)

6. Photon Light is made up of Photons!

7. Photon Light is made up of PHOTONS

8. 1 2 3 4 5 6 Electrically neutral Do not ionize Travels with speed of light Energy E = hf Massless Non-magnetic in nature Properties of Photon

9. Threshold Frequency (f ) Threshold Wave Length ( λ ) Work Function (W ) Stopping Potential

10. 1 2 3 4 5 6 Instantaneous process Electrons emits only if f > f f different for different materials W different for different materials K.E. MAX depends on frequency PE current increases with intensity of light Characteristic’s of Photoelectric effect

11. hf W mv 2   Einstein’s Photoelectric equation hf = W + mv 2  

12. Photoelectric cell - Construction

13. Photoelectric cell - Construction

14. Types of Photo electric cell Photo emissive cell Photo conductive cell Photo voltaic cell LOGO

15. Photoelectric cell - Working Incident light (E = hf) Here, A = anode C = cathode μA = micro ammeter B = Battery K = Key Rh = Rheostat

16. Light Dependent Resistor (LDR) 1 2 3 General purpose photoconductive cell Resistance decreases as light intensity increases Materials used: Cds and CdSe

17. 1 2 3 4 5 6 Automatic traffic signals Automatic switch on- off street lights Burglar Alarms Exposure meters in camera Reproduction of sound Lux meter- to measure light intensity Applications of Photoelectric cell

18. Variation of K.E. with frequency K.E. of ejected photo electrons increases with increase in frequency of light

19. Photoelectric effect - Animation

20. Photo electricity Presentation by: Mr. Pawar B N X- rays LASER