Q.16.  The following table gives the values of work function for a few photo sensitive metals.
 
S.NO   METAL WORK FUNCTION (eV)
1 Na 1.92
2 K 2.15                                                    
3   Mo   4.17

In each of these metals is exposed to radiations of wavelength 300mm, which of them will not emit photo electrons and why?

OR

By how much would the stopping potential for a given photosensitive surface go up if the frequency of the incident radiations were to be increased from 4 × 10 15   H z   t o   8 × 10 15   H z ? G i v e n   h =   6 . 4 × 10 - 34   J   - s , e = 1 . 6 × 10 - 19   C   a n d   c = 3 × 10 8   m s - 1

Dear student

Stopping potential is given by eVs=hv-WVs=hev-Wewhen v=4×1015 Hz    let Vs=V1when v=8×1015 Hz    let Vs=V2V1=hev1-We         and      V2=hev2-We V2-V1=hev2-v1 V2-V1=6.62×10-341.6×10-19×8×1015-4×1015V2-V1=16.55 V
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