Question

A student performs a photoelectric effect experiment in which light of various frequencies is incident on a photosensitive metal plate. This plate, a second metal plate, and a power supply are connected in a circuit, which also contains two meters, M₁ and M₂, as shown above.

The student shines light of a specific wavelength λ onto the plate. The voltage on the power supply is then adjusted until there is no more current in the circuit, and this voltage is recorded as the stopping potential V_s.

The student then repeats the experiment several more times with different wavelengths of light. The data, along with other values calculated from it, are recorded in the table below.

(a) Indicate which meter is used as an ammeter and which meter is used as a voltmeter by checking the appropriate spaces below.

                           M₁                 M₂

Ammeter            .........            ............

Voltmeter            .........            ............

(b) Use the data above to plot a graph of Kmax versus f on the axes below, and sketch a best-fit line through the data. 

(c) Use the best-fit line you sketched in part (b) to calculate an experimental value for Planck’s constant.

(d) If the student had used a different metal with a larger work function, how would the graph you sketched in part (b) be different? Explain your reasoning.

Answer 1

(a) Based on the series and parallel configuration. M₁ = voltmeter M₂ = ammeter

(b)

(c) From K = hf – φ (y=mx + b) … h is found with the slope using the 1st and 3rd points since they are on the line. h = 4.3 x 10^–15 eV-s

(d) The slope of the graph must be the same since its Planck’s constant. A larger work function will required a larger threshold frequency and thus shift the graph to the right. Additionally, the y intercept is the work function and to increase the y intercept, the graph would likewise have to be shifted to the right.