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2 marksParticulate Nature of Electromagnetic Radiation

CAPE Physics Unit 2 · May/June 2021 · Paper 2 · Question 3(b)(iii)

Electromagnetic radiation of wavelength 580 nm is incident on an uncharged surface of a metal X, in vacuo. Electrons are ejected from the metal surface and are attracted to a nearby positively charged electrode causing a photoelectric current to flow. As the potential on the nearby electrode is decreased, the photoelectric current decreases and becomes zero when the electrode potential is -0.3 V.

Calculate the maximum velocity of the photoelectrons ejected from the metal surface.

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  1. 3(a)(i)Determine log₁₀R for EACH value of x and complete Row 3 of Table 3.[2 marks]
  2. 3(a)(ii)Using the axes provided in Figure 6 on page 17, plot a graph of log₁₀R against x, ensuring that the x-axis extends to x = 3.0 mm. Draw the line of best fit…[3 marks]
  3. 3(a)(iii)Deduce the count rate at x = 2.8 mm.[3 marks]
  4. 3(a)(iv)Explain why the lower count rate values are more likely to be inaccurate.[2 marks]
  5. 3(b)(i)Describe the photoelectric effect and explain how the stopping potential is related to the kinetic energy of the ejected electrons.[4 marks]
  6. 3(b)(ii)Using the relationship between stopping potential, V_s, and maximum kinetic energy, show that v_max, the maximum speed of ejected electrons, is given by v_max…[3 marks]
  7. 3(c)(i)Describe how radiocarbon dating is used to determine the age of ancient organic materials.[4 marks]
  8. 3(c)(ii)A radioactive isotope of carbon found in a sample of 6.02 × 10^23 atoms of living wood has a decay constant of 3.84 × 10^–12 s^–1. Calculate its half-life in…[4 marks]
  9. 3(c)(iii)Calculate the rate of decay of C-14 in this sample.[3 marks]

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