(a)(i) State Einstein's equation of photoelectric effect (ii) What conservation principle does the equation represent?...
(a)(i) State Einstein's equation of photoelectric effect
(ii) What conservation principle does the equation represent?
(b) List three applications of photocells
(c) A photo emissive surface has a threshold frequency of 4.02 x 10\(^{14}\)Hz. If the surface is illuminated by light of frequency 5.0 x 10\(^{15}\)Hz, calculate the:
(i) threshold wavelength;
(ii) work function;
(iii) kinetic energy of the emitted photoelectrons. [ c = 3.0 x 10\(^{8}\) ms\(^{-1}\), h = 6.63 x 10\(^{-34}\) Js]
Explanation
(a)(i) E = W + K.E, where
E = energy of incident radiation
W = work function of metal
K.E. = Kinetic energy of ejected electrons
(ii) The equation represents the principle of conservation of energy.
(b) Applications of photocells:
1. for burglar alarm
2. for television cameras
3. automatic doors
4. automatic street lighting
5. automatic digital counters.
(c)(i) V = \(f_o\lambda_o\)
\(\lambda_o = \frac{v}{f_o} = \frac{3 \times10^8}{4.02 \times 10^{14}}\)
= 7.46 x 10\(^{-7}\)m
(ii) W = \(hf_o = 6.63 \times 10^{-34} \times 4.02 \times 10^{14}\)
= 2.67 x 10\(^{-19}\)J
(iii) K.E. = \(h (f - f_o) = 6.63 \times10^{-34} (5.0 \times 10^{15} - 4.02 \times 10^{14})\)
= 3.05 x 10\(^{-15}\)J