When a surface is irradiated with light of wavelength `4950 A`, a photoncurrent appears which vanishes if a retarding potential greater than 0.6 V is applied across the photo tube. When a different source of light is used, it is found that the critical retarding potential is changed to 1.1 V. Find the work function of the emitting surface and the wavelength of the second source. If the photoelectrons (after emission from the surface) are subjected to a magnetic field of 10 T, what chages will be observed in the above two retarding potentials?

Explanation

We know that
`hf_1=phi+(1)/(2)mv_1^(2)` and `(1)/(2)mv_1^2=eV_1`
`phi=hf_1-eV_1=(hc)/(lamda_1)-eV=((6.6xx10^(-34))xx(3xx10^(8)))/(4950xx10^(-10))-(1.6xx10^(-19))(0.6)`
`=3.04xx10^(-19)V`,`hf_2=phi+eV_2`
`(hc)/(lamda_2)=3.04xx10^(-19)+(1.6xx10^(-19))xx1.1=4.8xx10^(-19)`
`implieslamda_2=((6.6xx10^(34))xx(3xx10^(8)))/(4.8xx10^(-19))=4125A`