Particle Nature of Light Photon - UNSOLVED PRACTICE SET
Chapter: Dual Nature of Radiation and Matter | Topic: Particle Nature of Light Photon
PARTICLE NATURE OF LIGHT PHOTON - UNSOLVED PRACTICE SET
Topic: Particle Nature of Light Photon
Multiple Choice Questions
Q1. A photon is a quantum of:
- Electric field
- Electromagnetic radiation
- Gravitational field
- Sound energy
Q2. The energy of a photon is given by:
- E = h/ν
- E = hν
- E = hν²
- E = h/ν²
Q3. The momentum of a photon is given by:
- p = hν
- p = h/λ
- p = hλ
- p = λ/h
Q4. The rest mass of a photon is:
- Equal to its energy divided by c²
- Zero
- Equal to hν/c²
- Infinite
Q5. The number of photons emitted per second by a source of power P emitting light of frequency ν is:
- P/(hν)
- Phν
- Pν/h
- h/(Pν)
Q6. Photons do not carry:
- Energy
- Momentum
- Electric charge
- Angular momentum
Short Answer Questions
Q7. Define a photon. List three properties of photons that distinguish them from material particles.
Q8. Calculate the energy of a photon of wavelength 500 nm in joules and in eV.
Q9. Why does the concept of a photon contradict the classical wave theory of light? Explain.
Q10. A source emits light of wavelength 600 nm. Calculate the momentum of each photon.
Q11. How many photons per second are emitted by a 100 W sodium lamp assuming all energy is converted to light of wavelength 589 nm?
Q12. Why is the photon concept necessary to explain the photoelectric effect but not to explain interference?
Long Answer Questions
Q13. Describe the particle nature of light in terms of photons. Derive the expressions for the energy and momentum of a photon and discuss its properties.
Q14. Explain how the photon concept resolves the paradoxes of the photoelectric effect that could not be explained by wave theory. Discuss the dual nature of light.
Q15. Explain how the momentum of a photon is related to its wavelength. Discuss the significance of this relationship in understanding the interaction of light with matter.
Numerical & Application-based Problems
Q16. A monochromatic source of light emits photons of wavelength 400 nm. The power of the source is 10 W.
(a) Calculate the energy of each photon.
(b) Calculate the momentum of each photon.
(c) Calculate the number of photons emitted per second.
(d) If this light falls on a metal surface with work function 2.0 eV, calculate the maximum kinetic energy of the photoelectrons.
Q17. A laser pointer emits light of wavelength 650 nm with a power of 5 mW.
(a) Calculate the energy of each photon.
(b) Calculate the number of photons emitted per second.
(c) Calculate the force exerted by the laser beam when it is completely absorbed by a surface.
(d) Calculate the radiation pressure exerted on a surface of area 1 mm².
Q18. In your school's physics lab, a student investigates the properties of photons using various light sources.
(a) She uses a 60 W incandescent bulb that emits only 5% of its energy as visible light (average wavelength 550 nm). Calculate the number of visible photons emitted per second.
(b) She then compares this with a 10 W LED that converts 80% of its energy to visible light of the same average wavelength. Calculate the number of visible photons from the LED and compare it with the bulb.
(c) The student shines the LED light on a photocell with a caesium cathode (work function = 2.14 eV). Calculate the maximum kinetic energy of the emitted photoelectrons.
(d) A classmate argues that since photons have no mass, they cannot exert pressure on a surface. Explain why this is incorrect and calculate the force exerted by sunlight (intensity 1000 W/m²) on a 1 m² solar panel.
(e) Solar panels are becoming increasingly common on rooftops in India. Explain how the photon concept helps us understand the maximum efficiency of a solar cell and why it cannot exceed 100%.