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Ask iit jee aieee pet cbse icse state board experts Expert Question: photoelectric problem 2
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crack_iit (7)

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please help whether to do these kind of questions by analysing graphs or other way:
i am getting confused
the freq and intensity of a light source are both doubled.
(1)saturation photocurrent remains almost same
(2)max k.e. of photoelectrons is doubled
a.both true
b.1 true 2 false
c.1 false 2 true
d.both false
please reply soon!!
 
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jatinroxx (355)

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I would rather like doing such questions by equations.
Graph is also a good idea, but i dont find myself very comfortable with them.
As the intensity is doubled, the saturation photoelectric current will increase for sure.
Hence i is false
For the frequency,
Let v represent frequency,
KE1 max = hv - hvo
If v is doubled
KE2 max = 2hv - hvo = 2(hv - hvo) + hvo = 2KE1 + hvo
Hence the KE max becomes greater than twice the initial KE with doubling the frequency.
Hence ii is also false
Hence the answer is d

HOPE U GOT IT...
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crack_iit (7)

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but frnd!! ans here given in hcv2 pg no.364 is b...
but thanks for replying!!
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crack_iit (7)

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any more answers please!!!
make it quick
have to go..
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chimanshu_007 (11609)

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nooooooooooo
saturation current (cut off current or stopping potential all means same) and photoelectric current dont mean the same thing....stopping potential is that min -ive potential given to anode in a photocell fr wich the photoelectric current becomes zero , denoted by Vs , it doesnt depend on intensity of light.......

and abt K.E
 
let E1 and E2 be the K.E corr. to frequencies @ and 2@ . if Wo be the work func.
so
 
h@ = E1 + Wo
 
2h@ = E2 + Wo
 
dividing
 
2 = E2 + Wo / E1 + Wo
 
E2 = 2E1 + Wo
 
 
it means KE will be more than doubled , if freq. is doubled
 
 
ans will be b

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jus_look (81)

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ya...i agree with chimanshu...gud xplanation!!
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iitkgp_bipin (6498)

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Good work Himanshu.

Saturation current and photo-current are two different things. Dont confuse them. While the 2nd statement can easily be proved false by algebric relations. Also these can be proved by graphs.

Bipin Kumar Dubey
Chemical Dept.
IIT Kharagpur

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dream_iit (238)

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how it can be solved by graphs?????

neways good work...

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