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NEET · Physics · Atomic Physics
The work function of caesium (Cs) metal is 2 eV. When monochromatic...
The work function of caesium (Cs) metal is 2 eV. When monochromatic radiation beam of intensity (60 ) and frequency (6 10^{14} ), is falling normally on Cs plate of (6.6 \mathrm{~cm}^2) in a photocell then
(a) Energy of a photoelectron may be (8 10^{-20} )
(b) Stopping potential is 0.48 V
(c) Saturation current is 16 A
Correct choices are
Options
- AOnly b
- BOnly b & c
- COnly a & b
- Da, b, & c
Correct answer
D. a, b, & c
Step-by-step solution
Given data:
- Work function of Caesium ((\phi)=2 \mathrm{eV}=)
(2 \times 1.6 \times 10^{-19} \mathrm{ J}=3.2 \times 10^{-19} \mathrm{ J})
- Frequency of radiation ((f)=6 \times 10^{14}) Hz
- Area of the plate =
(6.6, \mathrm{ cm}^2=6.6 \times 10^{-4}, \mathrm{ m}^2)
- Intensity of radiation =
(60, \mathrm{ kW} / \mathrm{m}^2=60 \times 10^3, \mathrm{ W} / \mathrm{m}^2)
Step 1: Energy of incident photons
The energy of each photon is given by:
(E=6.626 \times 10^{-34} \times 6 \times 10^{14}=3.97 €)
Step 2: Maximum kinetic energy of ejected electrons
The maximum kinetic energy of the ejected electrons is given by the photoelectric equation:
(K_{\max }=E_{\text{photon }}-\phi)
(K_\max = 3.9756 \times 10^{-19})
- 3.2 (\times 10^{-19}=7.756 \times 10^{-20}, \text{J})
This value is very close to (8 \times 10^{-20}, \mathrm{ J}), so Statement (a) is approximately correct.
Step 3: Stopping potential
The stopping potential is given by:
(e V_0=K_{\max })
The stopping potential is given by:
()
This is very close to 0.48 V, so
Statement (b) is correct.
Step 4: Saturation current
To find the saturation current, we first calculate the total power incident on the plate:
()
Conclusion:
The correct choices are (4) (\mathrm{a}, \mathrm{b}, \& \mathrm{c}).