Light of wavelength 2475 Å is incident on barium . Photo electrons emitted describe a circle of radius 100 cm by a magnetic field of flux density `1/sqrt17xx10^(-5)` tesla. Find the work function of the barium . (Given `e/m=1.7xx10^11`)

Options

A. `1.8eV`
B. `2.1 eV`
C. `4.5 eV`
D. `3.3 eV`

Answer

C

Explanation

r (Radius) = `(sqrt(2mk))/(qB)`
`implies k = (q^2B^2r^2)/(2m) =(e/m)(eB^2r^2)/2`
`implies k =1/2 xx1.7 xx10^(11) xx1.6 xx10^(-19) xx[1/sqrt(17)xx10^(-5)]^(2)xx(1)^2`
`= 8 xx10^(-20) J = 0.5 eV`
`k_("max") = E-phi_0`
`impliesphi_0=((12375)/(2475))eV-0.5 eV = 4.5 eV`