Answer:
1. (b) 2.5 eV
2. (c) 430000 m/s
3. (a) The maximum velocity of any ejected electrons will decrease.
Explanation:
1)
From Einstein's Photoelectric Equation:
hc/λ = K.E + ∅
∅ = hc/λ - K.E
∅ = hc/λ - eV
where,
e = charge on electron = 1.6 x 10⁻¹⁹ C
V = Stopping Potential = 0.52 volts
h = 6.625 x 10⁻³⁴ J.s
c = speed of light = 3 x 10⁸ m/s
λ = wavelength = 405 nm = 4.05 x 10⁻⁷ m
∅ = Work Function = ?
Therefore,
∅ = (6.625 x 10⁻³⁴ J.s)(3 x 10⁸ m/s)/(4.05 x 10⁻⁷ m) - (1.6 x 10⁻¹⁹ C)(0.52 volts)
∅ = 4.9 x 10⁻¹⁹ J - 0.832 x 10⁻¹⁹ J
∅ = (4.075 x 10⁻¹⁹ J)(1 eV)/(1.6 x 10⁻¹⁹ J)
∅ = 2.5 eV
therefore, correct answer is"
<u>(b) 2.5 eV</u>
2)
K.E = (1/2)mv² = eV
where,
m = mass of electron = 9.1 x 10⁻³¹ kg
v = speed = ?
therefore,
(1/2)(9.1 x 10⁻³¹ kg)v² = (1.6 x 10⁻¹⁹ C)(0.52 volts)
v = √(0.18 x 10¹² m²/s²)
v = 0.43 x 10⁶ m/s = 430000 m/s
Correct option is:
<u>(c) 430000 m/s</u>
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3.
The decrease in power at constant wavelength means decrease in voltage, that results in the decrease of kinetic energy of electrons. So, correct option is:
<u>(a) The maximum velocity of any ejected electrons will decrease.</u>
