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CBSE Class 12-science Answered

Radiation of wave length 180 nm ejects photo electrons from a plate whose work function is 2.0eV. If a uniform magnetic field of flux density 5.0 x 10raise to -5 T is applied to the plate, what should be the radius of the path followed by electrons ejected normally from the plate with maximum energy?
Asked by rutujasarangmehta | 15 Mar, 2016, 06:53: PM
answered-by-expert Expert Answer
h = 6.62 × 10-34 Js; e = 1.6 × 10-19 C; c = 3 × 108m/s; m = 9.1 × 10-31
Maximum kinetic energy of the ejected photo-electron is
begin mathsize 14px style straight E subscript max equals 1 half mv subscript max superscript 2 equals hc over straight lambda minus straight ϕ subscript 0 equals fraction numerator 6.62 cross times 10 to the power of negative 34 end exponent cross times 3 cross times 10 to the power of 8 over denominator 180 cross times 10 to the power of negative 9 end exponent end fraction minus 2 cross times 1.6 cross times 10 to the power of negative 19 end exponent equals 7.8 cross times 10 to the power of negative 19 end exponent straight J straight v subscript max equals square root of fraction numerator 2 straight E subscript max over denominator straight m end fraction end root equals square root of fraction numerator 2 cross times 7.8 cross times 10 to the power of negative 19 end exponent over denominator 9.1 cross times 10 to the power of negative 31 end exponent end fraction end root equals 1.3093 cross times 10 to the power of 6 space straight m divided by straight s end style
Radius of circular path in the magnetic field of induction B is given by
begin mathsize 14px style Bev equals mv squared over straight r straight r equals mv over eB equals fraction numerator 9.1 cross times 10 to the power of negative 31 end exponent cross times 1.3093 cross times 10 to the power of 6 over denominator 1.6 cross times 10 to the power of negative 19 end exponent cross times 5.0 cross times 10 to the power of negative 5 end exponent end fraction equals 0.149 space straight m end style
Answered by Faiza Lambe | 16 Mar, 2016, 08:27: AM

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