Radiation of wavelength `lambda` in indent on a photocell . The fastest emitted electron has speed `v` if the wavelength is changed to `(3 lambda)/(4)` , then speed of the fastest emitted electron will be

Options

A. Smaller than `sqrt((4V)/3`
B. Greater than `sqrt((4V)/3`
C. 2V
D. Zero

Answer

B

Explanation

From Einstein's photoelectric effect `eq^(n)`
`(hc)/lamda = phi + 1/2mv^(2)`
`(4hc)/(3lamda) = phi_(0) + 1/2mv_(1)^(2)`
`implies 4/3(phi_(0)+1/2mv^(2))=phi_(0) + 1/2mv_(1)^(2)` ltbegt `implies 1/2mv_(1)^(2)=phi_(0)/3+1/2m(sqrt((4)/(3)v))^(2)implies v_(1) gtsqrt((4)/(3))`