1. Do Now: A helium-neon laser has a wavelength of 650nm. 1)Calculate the frequency of the laser light 2)Calculate the energy of each photon of the laser light 3)Convert this energy to units of eV (electron volts) Tūrei, 26 Kohi-tātea 2016 E = hf v = fλ h = 6.63 x 10 -34 Js c = 3.00 x 10 8 ms -1 e = 1.60 x 10 -19 C

2. Today’s Kaupapa (Learning Outcomes): 1)Explain and calculate the work function and cut-off voltage for the photoelectric effect

3. Watch: Photoelectric effect - work function and stopping potential - 5min 22sec

4. Board notes

5. The power supply provides an opposing voltage to the p.e. cell The power supply provides an opposing voltage to the p.e. cell The variable voltage is adjusted until the current in the circuit is zero The variable voltage is adjusted until the current in the circuit is zero LIGHT V

6. Which metal would make the better photocell? Different metals have different f 0 ’s and work functions - why? Depends on how tightly they hold onto their electrons f EkEk f0f0 f0f0 Cu Pb How would you measure E K ?

7. Blue light with f = 7.0 x 10 14 Hz shines on a photoelectric cell which has a 1.63V cut-off voltage 1)What is the energy of the blue light photons? 2)What is the maximum kinetic energy of the emitted electrons? 3)What is the work function of the metal 4)What is the threshold frequency at which electrons are first emitted?