Do Now: A helium-neon laser has a wavelength of 650nm. Rāhina, 24 Paenga-whāwhā, 2017 A helium-neon laser has a wavelength of 650nm. Calculate the frequency of the laser light Calculate the energy of each photon of the laser light Convert this energy to units of eV (electron volts) E = hf v = fλ h = 6.63 x 10-34 Js c = 3.00 x 108 ms-1 e = 1.60 x 10-19 C

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

Which metal would make the better photocell? f Ek f0 Cu Pb Different metals have different f0’s and work functions - why? Depends on how tightly they hold onto their electrons Which metal would make the better photocell? How would you measure EK?

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 LIGHT V

Blue light with f = 7.0 x 1014Hz shines on a photoelectric cell which has a 1.63V cut-off voltage What is the energy of the blue light photons? What is the maximum kinetic energy of the emitted electrons? What is the work function of the metal What is the threshold frequency at which electrons are first emitted?

Reminders: Today: complete Activity 11B H/W Set 3 (Nuclear) is due today H/W Set 1 (Photoelectric) due Thurs 28th Mar You should also be working on the NZIP exam questions on Nuclear I gave you last week – you’ll be getting another set on photoelectric this Wed Uni trip: Monday 8th April (Week 11) Internal: Week 12