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Ultraviolet light of wavelength 2271Å fr...

Ultraviolet light of wavelength 2271`Å` from a 100 W mercury source irradiates a photocell made of molybdenum metal. If the stopping potential is 1.3 volt, estimate the work function of the metal. How would the photocell respond to a high intesity `( = 10^(5) W m^(-2))` red light of wavelength `6328Å` produced by He-Ne laser ?

Text Solution

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Given data `:`
`V_(0)= 1.3 ` volt
`lambda = 2271 xx 10^(-10) m`
We know that `hv = hv_(0)+(1)/(2) m_("max")^(2)`
or `hv =phi_(0) +eV_(0)`
`phi_(0) = hv-eV_(0) `or `phi_(0) = ( hc)/( lambda) - eV_(0)`
`phi_(0) + ( 6.62 xx 10^(-34) xx 3 xx 10^(8))/( 2271 xx 10^(-10)) - 1.3 xx 1.6 xx 10^(-19)` On simplification,` phi_(0) = 6.665 xx 10^(-19) J`
or `phi_(0)+ ( 6.665 xx 10^(-19) )/( 1.6 xx 10^(-19)) eV`
`= 4.166 eV`
Again,` phi_(0)= hv_(0) + (hc)/( lambda_(0)) `or `hv_(0)= ( hc)/( phi_(0))`
`= ( 6.62 xx 10^(-34) xx 3 xx 10^(8))/( 6.665 xx 10^(-19))m`
`= 2.98 xx 10^(-7) m= 2980 Å`
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