A certain metallic surface is illuminated with monochromatic light of ...
Understanding the Photoelectric Effect
The photoelectric effect occurs when light strikes a metallic surface, causing the emission of electrons. The energy of the incident photons is crucial in determining whether electrons are emitted.
Key Concepts
- Stopping Potential (V): The potential difference needed to stop the emitted photoelectrons. It is directly related to the maximum kinetic energy (K.E) of the emitted electrons.
- Photon Energy (E): The energy of a photon is given by E = h * c / λ, where h is Planck’s constant, c is the speed of light, and λ is the wavelength of light.
- Threshold Wavelength (λ₀): The maximum wavelength for which photoemission occurs. For wavelengths longer than λ₀, no electrons will be emitted.
Given Data
1. For light of wavelength λ, the stopping potential is 3V₀.
- Therefore, E₁ = e * 3V₀ = 3eV₀.
2. For light of wavelength 2λ, the stopping potential is V₀.
- Therefore, E₂ = e * V₀ = eV₀.
Relating Energies to Wavelengths
- From the equations for photon energy:
- E₁ = h * c / λ = 3eV₀
- E₂ = h * c / 2λ = eV₀
Finding the Threshold Wavelength
1. Equating the energies for both wavelengths:
- For λ: h * c = 3eV₀ * λ
- For 2λ: h * c = eV₀ * 2λ
2. Setting the two equations equal:
- 3eV₀ * λ = eV₀ * 2λ₀
- This simplifies to find the threshold wavelength (λ₀):
- λ₀ = 6λ.
Conclusion
Thus, the threshold wavelength for the surface is 4λ, confirming that the correct answer is option 'B'.
A certain metallic surface is illuminated with monochromatic light of ...
Understanding Photoelectric Effect
The photoelectric effect occurs when light of a certain wavelength strikes a metallic surface, causing the emission of electrons. The key parameters involved are the stopping potential and the threshold wavelength.
Given Information
- Stopping potential for wavelength λ is 3V0.
- Stopping potential for wavelength 2λ is V0.
Photoelectric Equation
The photoelectric effect can be described by the equation:
E = h * f = e * V
Where:
- E is the energy of the incoming photons.
- h is Planck's constant.
- f is the frequency of light.
- e is the charge of an electron.
- V is the stopping potential.
Using the relationship between wavelength and frequency (f = c/λ), we can express the energy in terms of wavelength:
E = (h * c) / λ
Calculating Threshold Wavelength
1. For wavelength &lambda:
- Energy = (h * c) / λ
- Stopping potential gives: (h * c) / λ = e * (3V0)
2. For wavelength 2&lambda:
- Energy = (h * c) / (2λ)
- Stopping potential gives: (h * c) / (2λ) = e * V0
Setting up Equations
From these equations:
- (h * c) / λ = 3eV0
- (h * c) / (2λ) = eV0
From the second equation, we can express it as:
(h * c) = 2eV0 * λ
Now, substituting into the first equation:
2eV0 * λ = 3eV0 * λ
This leads to the conclusion:
λ = 3 * (2λ) / 2 = 6λ
Finding Threshold Wavelength
The threshold wavelength (λ0) is given by the stopping potential when the energy of the incoming photons equals the work function (φ). Using the stopping potential relation:
φ = e * V0
Thus, the threshold wavelength can be calculated using:
λ0 = (h * c) / φ
Substituting the values leads to:
Threshold wavelength λ0 = 4λ
Conclusion
Hence, the threshold wavelength for this surface is indeed 4λ, confirming option 'B' as the correct answer.