Physics Chapter on Alpha Scattering

General Instructions

• This document contains 12 questions. All questions are compulsory.
• The document is divided into three sections: A, B, and C.
• Section A comprises questions 1-3, each worth 2 marks.
• Section B has questions 4-11, each worth 3 marks.
• Question 12 is a case study question, worth 5 marks.
• There are internal choices in some questions.
• Students can use log tables, but calculators are not permitted.
• Important constants are included: c = 3 x 10⁸ m/s, h = 6.63 x 10⁻³⁴ Js, e = 1.6 x 10⁻¹⁹ C, μ₀ = 4π x 10⁻⁷ Tm A⁻¹, ε₀ = 8.854 x 10⁻¹² C² N⁻¹ m⁻², (4πε₀)⁻¹ = 9 x 10⁹ N m² C⁻². Also, masses of electron, neutron, and proton are provided.
• The time allotted for reading the paper before writing answers is 15 minutes.

Section A

• Question 1:

  • (a) requires a graph showing the variation of the number of scattered alpha particles with scattering angle in a Geiger-Marsden experiment, and two conclusions to be drawn from this graph.
  • (b) requires plotting graphs to show the variation of photoelectric current with collector plate potential, given varying frequencies and intensities of incident radiation (graphs for the same intensity but different frequencies and the same frequency but different intensities).

• Question 2: Explain the difference between intrinsic and extrinsic semiconductors. Explain why an extrinsic semiconductor is electrically neutral despite having unequal electron and hole densities.

• Question 3: Draw and label energy band diagrams for n-type and p-type semiconductors at a temperature greater than absolute zero, showing donor and acceptor energy levels. Provide the significance of these levels.

Section B

• Question 4:
• (a) Calculate the distance of the first minimum and the second maximum in a diffraction pattern created by a parallel beam of light of wavelength 600 nm incident on a slit of width 0.2 mm. The observation is made on a screen 1 meter away.
• (b) Two lenses with different refractive indices and curvatures are in contact. Calculate the ratio of their powers and the nature of the combined lens.

Section C

• Question 12: The principle of superposition is used to understand the interference of light waves. Given a set of waves (y₁=a sin ωt, y₂=a sin 2ωt, y₃=a sin (2ωt+φ), y₄=a sin(4ωt+π/2)), determine which pairs of waves will lead to interference.