Form 5 Physics Bab 7: Quantum Physics
Instructions
Answer all structured questions. Show clear working for numerical problems. Take h = 6.63 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m s⁻¹, e = 1.6 × 10⁻¹⁹ C, and m_e = 9.1 × 10⁻³¹ kg where applicable.
10 questions · 29 marks total
1. True or False: According to de Broglie's hypothesis, a moving tennis ball has a shorter wavelength than a moving electron travelling at the same speed.
True / False · 1m2. Fill in the blank: The minimum frequency of light required to emit photoelectrons from a metal surface is called the ________ frequency.
Fill in the Blank · 1m3. True or False: Increasing the intensity of incident light above the threshold frequency increases the maximum kinetic energy of the emitted photoelectrons.
True / False · 1m4. An electron in an electron microscope is accelerated through a potential difference of 500 V. (a) Calculate the kinetic energy gained by the electron in Joules. (b) Calculate the velocity of the electron. (c) Calculate the de Broglie wavelength of the accelerated electron.
Short Answer · 5m5. A sodium metal surface has a work function (Φ) of 3.65 × 10⁻¹⁹ J. (a) Define work function. (b) Calculate the threshold frequency (f₀) of sodium. (c) Calculate the threshold wavelength (λ₀) of sodium.
Short Answer · 4m6. The diagram of a photocell circuit shows light shining on a curved metal cathode. (a) State how the photoelectric current changes when the light source is moved closer to the photocell. (b) Explain your answer in (a) based on photon theory.
Short Answer · 3m7. Monochromatic light of wavelength 450 nm shines on a Caesium metal surface with a work function of 3.43 × 10⁻¹⁹ J. (a) Calculate the energy of an incoming light photon in Joules. (b) Calculate the maximum kinetic energy (K_max) of the emitted photoelectrons. (c) Calculate the maximum velocity (v_max) of the emitted photoelectrons.
Short Answer · 5m8. In a photoelectric experiment, a stopping potential of 1.25 V is required to drop the photocurrent to zero when light of frequency 7.5 × 10¹⁴ Hz illuminates a cathode. (a) Calculate the maximum kinetic energy of the photoelectrons in Joules. (b) Determine the work function (Φ) of the metal cathode material in Joules.
Short Answer · 4m9. Explain how the photoelectric effect is applied in an automatic dusk-to-dawn street lighting control system. (a) Describe the state of the photocell sensor during daylight. (b) Explain how the system triggers the street light when night falls.
Short Answer · 4m10. Which of the following physical phenomena provides direct evidence for the particle nature of light waves?
Multiple Choice · 1m