Answer:
i) No electron is emitted. Hence, no kinetic energy or velocity of emitted electron
ii) KE = 6.85 x 10⁻¹⁹ J; v = 1.23 x 10⁶ m/s
Explanation:
Using the formula: Kinetic energy, KE = hc/λ - E₀
where h = the Plank constant 6.63 x 10⁻³⁴ J s,
c is velocity of light = 3.00 x 10⁸ m/s
λ = wavelength of incident light in nm
E₀ = work function in Joules
Note: 1 eV = 1.602×10⁻¹⁹ Joules
Also, using KE = 1/2 mv²
v = √(2KE/m)
where m is mass of electron = 9.11 x 10⁻³¹ Kg
i) KE = hc/λ - E₀
KE = (6.63 x 10⁻³⁴ Js x 3.00 x 10⁸ m/s) / 650 x 10⁻⁹ m - (2.09 x 1.602×10⁻¹⁹ J)
KE = 3.06 x 10⁻¹⁹ J - 3.35 x 10⁻¹⁹ = - 2.9 x 10⁻²⁰ J
Since KE is negative, no electron is emitted. Thus, there is no kinetic energy or velocity of electron.
ii) KE = hc/λ - E₀
KE = (6.63 x 10⁻³⁴ Js x 3.00 x 10⁸ m/s) / 195 x 10⁻⁹ m - (2.09 x 1.602×10⁻¹⁹ J)
KE = 10.2 x 10⁻¹⁹ J - 3.35 x 10⁻¹⁹
KE = 6.85 x 10⁻¹⁹ J
Velocity, v = √(2KE/m)
v = √( 2 x 6.85 x 10⁻¹⁹ J / 9.11 x 10⁻³¹ Kg)
v = 1.23 x 10⁶ m/s
