Stopping Potential - UNSOLVED PRACTICE SET
Chapter: Dual Nature of Radiation and Matter | Topic: Stopping Potential
STOPPING POTENTIAL - UNSOLVED PRACTICE SET
Topic: Stopping Potential
Multiple Choice Questions
Q1. The stopping potential is defined as:
- The minimum potential required to accelerate photoelectrons
- The minimum negative potential required to stop the fastest photoelectronstion B
- The potential at which photoelectric current is maximum
- The potential difference across the photocell
Q2. The relationship between stopping potential (Vโ) and maximum kinetic energy (K_max) is:ere...
- K_max = eVโ
- K_max = e/Vโ
- K_max = Vโ/e
- K_max = Vโยฒ/e
Q3. The stopping potential depends on:
- The intensity of incident light
- The frequency of incident light
- The area of the cathode
- The distance between cathode and anode
Q4. If the frequency of incident light is doubled, the stopping potential:
- Remains the same
- Doubles
- Increases but not necessarily doubles
- Becomes half
Q5. The graph of photoelectric current versus collector plate potential shows that:
- The current increases indefinitely with potential
- The current saturates at a certain positive potential
- The current is zero at all negative potentials
- The current is independent of potential
Q6. The stopping potential for a given photosensitive surface is independent of:
- The frequency of incident light
- The intensity of incident light
- The work function of the material
- The nature of the material
Short Answer Questions
Q7. Define stopping potential. How is it related to the maximum kinetic energy of photoelectrons?
Q8. Why does the photoelectric current not increase indefinitely with increasing positive potential on the collector?
Q9. Draw a graph showing the variation of photoelectric current with collector plate potential for:
(a) Different intensities of incident light (same frequency)
(b) Different frequencies of incident light (same intensity)
Q10. Why is the stopping potential negative with respect to the emitter?
Q11. The stopping potential for a metal is 1.5 V when illuminated with light of frequency 8 ร 10ยนโด Hz. What does this tell you about the maximum kinetic energy of the photoelectrons?
Q12. Why does the stopping potential remain unchanged when the intensity of incident light is increased?
Long Answer Questions
Q13. Explain the concept of stopping potential with a diagram. Derive the relationship between stopping potential and the maximum kinetic energy of photoelectrons.
Q14. Draw and explain the graph of photoelectric current versus potential difference between the collector and emitter for:
(a) Different intensities of incident light (same frequency)
(b) Different frequencies of incident light (same intensity)
Discuss the significance of the saturation current and stopping potential in each case.
Q15. Explain how the measurement of stopping potential is used to verify Einstein's photoelectric equation. How does this experiment provide a direct method to determine Planck's constant?
Numerical & Application-based Problems
Q16. Light of wavelength 250 nm is incident on a metal surface having a work function of 3.5 eV.
(a) Calculate the energy of each incident photon.
(b) Calculate the maximum kinetic energy of the emitted photoelectrons.
(c) Calculate the stopping potential.
(d) If the intensity of the incident light is increased by a factor of 4, what will be the new stopping potential?
Q17. The stopping potential for a photosensitive surface is measured for different frequencies of incident light:
Table
Frequency (ร10ยนโด Hz) Stopping Potential (V)
8.0 0.60
9.0 1.02
10.0 1.43
11.0 1.85
(a) Plot a graph of stopping potential versus frequency.
(b) From the graph, determine the threshold frequency.
(c) Calculate the work function of the material.
(d) Using the graph, calculate Planck's constant.
Q18. In your school's physics lab, a student sets up a photoelectric experiment using a vacuum photocell with a potassium cathode (work function = 2.3 eV).
(a) She illuminates the cathode with light of wavelength 400 nm and measures a photoelectric current. She then applies a negative potential to the collector and finds that the current drops to zero at โ0.8 V. Verify this stopping potential using Einstein's photoelectric equation.
(b) The student then uses light of wavelength 500 nm and measures the stopping potential again. Predict whether the stopping potential will increase, decrease, or remain the same, and calculate its new value.
(c) The student connects a microammeter in series and measures the saturation current as 2 ฮผA. Calculate the number of photoelectrons emitted per second. If the intensity of light is doubled, what will be the new saturation current?
(d) A classmate suggests that by applying a very large positive potential, we can increase the kinetic energy of the photoelectrons beyond the value given by Einstein's equation. Explain why this is not possible.