Paper 4 Quantum Physics Drills

Q1 Determination of the Planck Constant

A student measures the stopping potential $V_s$ for several frequencies $f$ of monochromatic light incident on the same metal surface.

| $f$/$10^{14}\mathrm{Hz}$ | 5.2 | 5.8 | 6.4 | 7.0 | 7.6 | 8.2 | |---:|---:|---:|---:|---:|---:|---:|---:| | $V_s$/V | 0.15 | 0.40 | 0.65 | 0.90 | 1.14 | 1.39 |

1. Plot a graph of $V_s$ against $f$ and draw a best-fit straight line. [5]
2. Determine the gradient in $\mathrm{V}\mathrm{H}{\mathrm{z}}^{-1}$. [2]
3. Use $e{V}_s=hf-\Phi$ to determine the Planck constant $h$. [2]
4. Use the frequency-axis intercept to determine the work function $\Phi$ in eV. [2]
5. State two experimental factors that could produce scatter in the stopping-potential readings. [2]

Q2 X-ray Spectrum Investigation

1. Explain how changing accelerating voltage affects the minimum wavelength. [2]
2. Explain how changing target material affects characteristic peaks. [2]
3. State one safety precaution for X-ray production. [1]