The method and the results are on the photoelectric effect lab. Do the analysis yourself first, then check the answers below.
Quick answer: Light is absorbed and emitted in photons, each carrying energy E = hf. These answers go with the AP Physics 2 lab on photoelectric effect: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Here are the photoelectric effect lab answers for AP Physics 2: graph, calculations, uncertainties and conclusion. First do the lab yourself, then compare, and go back to the lesson if needed.
Model answers use the sample table above. Your readings will differ a little, so focus on the method: reciprocal wavelength, gradient, conversion to h and an honest comparison with the accepted value.
Level: AP Physics 2 (algebra-based) · Curriculum: AP P2 Unit 15
h = gradient × e / c = 1.23 × 10⁻⁶ × 1.60 × 10⁻¹⁹ / 3.00 × 10⁸ = 6.56 × 10⁻³⁴ J·s.
Question 5 Percentage difference
(6.63 − 6.56) / 6.63 × 100 = 1.1 %, which is within the experimental uncertainty.
Question 6 Meaning of the intercept
The theory predicts zero intercept. The line gives V = 1.91 − 1.23 × 1.575 = −0.03 V, which is very close to zero.
Question 7 Predict a violet LED
1/0.405 = 2.469 µm⁻¹, so V = 1.23 × 2.469 = 3.04 V. Uncertainty: judging when the LED first glows depends on the observer and the room light, so the voltage is uncertain by about ±0.03 V; a photodiode would be better.
