In a photoelectric experiment a parallel beam of monochromatic light w...
Given data:
- Power of incident light (P) = 200 W
- Work function of the cathode (ϕ) = 6.25 eV
- Threshold frequency (ν₀) = ?
- Efficiency of photoelectron emission (η) = 100%
- Potential difference between cathode and anode (V) = 500 V
- Force experienced by the anode due to electron impact (F) = n × 10⁻⁴ N
- Mass of the electron (mₑ) = 9 × 10⁻³¹ kg
- 1.0 eV = 1.6 × 10⁻¹⁹ J
Calculating the threshold frequency:
The work function (ϕ) represents the minimum energy required to remove an electron from the cathode. This energy is given by the equation:
ϕ = hν₀
Where h is the Planck's constant (6.63 × 10⁻³⁴ J·s) and ν₀ is the threshold frequency.
To convert the work function from electron volts (eV) to joules (J), we use the conversion factor:
1.0 eV = 1.6 × 10⁻¹⁹ J
Therefore, ϕ = 6.25 eV × (1.6 × 10⁻¹⁹ J/eV) = 1 × 10⁻¹⁸ J
Using the equation ϕ = hν₀, we can solve for ν₀:
ν₀ = ϕ / h = (1 × 10⁻¹⁸ J) / (6.63 × 10⁻³⁴ J·s) = 1.51 × 10¹⁵ Hz
Calculating the energy of incident photons:
The power (P) of the incident light is given by the equation:
P = nhν
Where n is the number of photons incident per second, h is the Planck's constant, and ν is the frequency of the incident light.
Rearranging the equation, we get:
n = P / (hν)
Substituting the given values, we have:
n = 200 W / (6.63 × 10⁻³⁴ J·s × 1.51 × 10¹⁵ Hz) ≈ 1.85 × 10²⁰ photons/s
Calculating the force experienced by the anode:
The force (F) experienced by the anode due to the impact of electrons can be calculated using the equation:
F = nqE
Where n is the number of electrons incident per second, q is the charge of an electron, and E is the electric field strength.
Since all emitted electrons are incident normally on the anode and absorbed, the number of electrons incident per second is equal to the number of photons incident per second, which is n = 1.85 × 10²⁰ electrons/s.
The charge of an electron (q) is -1.6 × 10⁻¹⁹ C.
Substituting the given values, we have:
n × 10⁻⁴ N = (1.85 × 10²⁰ electrons/s) × (-1.6 × 10⁻
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