Photoelectric Effect Observations - UNSOLVED PRACTICE SET
Chapter: Dual Nature of Radiation and Matter | Topic: Photoelectric Effect Observations
PHOTOELECTRIC EFFECT OBSERVATIONS - UNSOLVED PRACTICE SET
Topic: Photoelectric Effect Observations
Multiple Choice Questions
Q1. The photoelectric effect demonstrates:
- The wave nature of light only
- The particle nature of light
- Both wave and particle nature equally
- Neither wave nor particle nature
Q2. In the photoelectric effect experiment, photoelectrons are emitted from a metal surface when:
- Any light falls on it
- Light of sufficiently high frequency falls on it
- Intense light of any frequency falls on it
- The metal is heated to a high temperature
Q3. The photoelectric current depends on:
- The frequency of incident light only
- The intensity of incident light only
- Both the frequency and intensity of incident light
- Neither the frequency nor the intensity
Q4. For a given photosensitive material, there exists a certain minimum frequency below which no photoelectrons are emitted, no matter how intense the light is. This frequency is called:
- Resonant frequency
- Threshold frequency
- Cut-off frequency
- Both (b) and (c)
Q5. The maximum kinetic energy of photoelectrons depends on:
- The intensity of incident light
- The frequency of incident light
- The area of the metal surface
- The time for which light falls
Q6. In a typical photoelectric effect setup, the photoelectric current increases with the intensity of incident light because:
- The energy of each photon increases
- The number of photons incident per unit time increases
- The work function of the metal decreases
- The threshold frequency decreases
Short Answer Questions
Q7. List the main observations of the photoelectric effect that cannot be explained by the wave theory of light.
Q8. Why does the photoelectric effect not occur when the frequency of incident light is below the threshold frequency, even if the intensity is very high?
Q9. In a photoelectric experiment, the photoelectric current is found to be proportional to the intensity of incident light. Explain this observation.
Q10. Why is the photoelectric effect considered as evidence for the particle nature of light?
Q11. What happens to the maximum kinetic energy of photoelectrons when the intensity of incident light is increased, keeping the frequency constant?
Q12. Why does the photoelectric effect occur almost instantaneously (within 10⁻⁹ s) when light falls on the metal surface?
Long Answer Questions
Q13. Describe the experimental setup for studying the photoelectric effect. Explain how the photoelectric current, stopping potential, and maximum kinetic energy of photoelectrons are measured.
Q14. Discuss the key observations of the photoelectric effect. Explain why each observation poses a challenge to the classical wave theory of light.
Q15. Explain the effect of the following on the photoelectric emission:
(a) Increasing the intensity of incident light (frequency constant)
(b) Increasing the frequency of incident light (intensity constant)
(c) Changing the photosensitive material
Numerical & Application-based Problems
Q16. In a photoelectric experiment, the following data is obtained for a sodium surface:
Threshold wavelength = 540 nm
Wavelength of incident light = 400 nm
(a) Calculate the threshold frequency of sodium.
(b) Calculate the work function of sodium in eV.
(c) Calculate the maximum kinetic energy of the emitted photoelectrons.
(d) Calculate the maximum speed of the emitted photoelectrons.
Q17. A photosensitive surface has a work function of 2.0 eV. Light of wavelength 400 nm is incident on it.
(a) Calculate the energy of each incident photon in eV.
(b) Determine whether photoelectric emission will occur.
(c) If emission occurs, calculate the maximum kinetic energy of the photoelectrons.
(d) Calculate the stopping potential required to stop the fastest photoelectrons.
Q18. In your school's physics lab, a student performs a photoelectric effect experiment using a photocell with a potassium cathode.
(a) The student shines light of wavelength 500 nm and measures a photoelectric current. She then increases the intensity of this light while keeping the wavelength constant. Predict how the photoelectric current and the maximum kinetic energy of photoelectrons will change, and explain your reasoning.
(b) The student then uses light of wavelength 600 nm and finds no photoelectric current, even at very high intensity. Explain this observation and calculate the minimum frequency required for potassium if its work function is 2.3 eV.
(c) The student replaces the potassium cathode with a caesium cathode (work function = 2.14 eV) and uses light of wavelength 550 nm. Calculate the maximum kinetic energy of the emitted photoelectrons.
(d) A classmate argues that if we wait long enough, even low-frequency light will eventually eject electrons because energy accumulates over time. Explain why this argument is incorrect based on the observations of the photoelectric effect.