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A student performs an experiment on phot...


A student performs an experiment on photoelectric effect,using two materials A and B.A plot `V_("stop")vs` v is given in figure.
(i)Which material A or B has a higher work function?
(ii)Given the electric charge of an electron`=1.6xx10^(-19)`C,find the value of the h obtained from the experiment for both A and B.Comment on whether it is consistent with Einstein's theory:

Text Solution

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(i)Work function ,`phi_(0)=hf_(0)`
(where `f_(0)`=threshold frequency)
`therefore phi_(0)propf_(0)` ……..(1)
From the figure ,
`f_(0)A=5xx10^(14)`Hz
`f_(0)B=10xx10^(14)Hz`
`impliesf_(0)Bgtf_(0)A`
`implies` From relation(1),
`phi_(0)Bgtphi_(0)A`
(ii)We know that slope of graph of |`V_(0)|tof`
Gives us value of `((h)/(e))`.Hence
Slope of graph for A,
`tantheta_(1)=(PQ)/(QR)`
`therefore (h)/(e)=(2)/(5xx10^(14))=0.4xx10^(-14)`
`therefore h=0.4xx10^(-14)xxe`
`therefore h=0.4xx10^(-14)xx1.6xx10^(-19)`
`therefore h=6.4xx10^(-34)Js` .......(2)
Slope of graph for B,
`tantheta_(2)=(ST)/(QT)`
`therefore (h)/(e)=(2.5)/(5xx10^(14))=0.5xx10^(14)`
`therefore h=0.5xx10^(-14)xxe`
`=0.5xx10^(-14)xx1.6xx10^(19)`
`h=8xx10^(-34)Js` ..........(3)
Thus ,here value of h are obtained different from the graphs for A and B.Hence ,above experimental observations are not consistent with Einstein.s theory.
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