2. 1© Manhattan Press (H.K.) Ltd. 23.1 Quantum theory

3. 2 © Manhattan Press (H.K.) Ltd. 23.1 Quantum theory (SB p. 134) Quantum theory Einstein presented - light energy consisting of packets of EM energy According to Planck, the energy emitted or absorbed by the atoms in a black surface is in the form of indivisible packets which he called quanta. Energy in each quantum (E) = hf h = Planck constant = 6.63 x 10 -34 J s

4. 3 © Manhattan Press (H.K.) Ltd. 23.1 Quantum theory (SB p. 135) Quantum theory The light quanta (or electromagnetic radiations) are known as photons. The energy of a photon also is: Energy of photon (E) = hf = hc/ Go to Example 1 Example 1

5. 4 © Manhattan Press (H.K.) Ltd. End

6. 5 © Manhattan Press (H.K.) Ltd. Q: Q: A beam of red light, wavelength 700 nm, has 3 × 10 6 photons per second. It is able to maintain an increase in temperature of 0.2 K when incident on a thermopile. How many photons per second is required to maintain the same increase in temperature when a beam of blue light of wavelength 400 nm is used?. Solution 23.1 Quantum theory (SB p. 135)

7. 6 © Manhattan Press (H.K.) Ltd. Solution: To maintain the same increase in temperature, Energy per second supplied by blue light = Energy per second supplied by red light Return to Text 23.1 Quantum theory (SB p. 135)