IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry

fwks_phoenix

Q. Violet light lambda=400oA of intensity 4 watt/m-sqaure falls normally on a surface of area 10cmx20cm.Find
the energy received by the surface per second.
the answer is 0.08J
can u tell y the formula
E=1Acostheta is used to get the answer ?? shouldn't theta b 90 then, so wouldn't the expression bcum zero ?

i spotted a line in my material : "electrons are emitted only if the frequency is greater than the threshold frequency"
won't electrons b emitted when the frequency is equal to threshold frequency (they have to b emitted..is the statement wrong?)???

can u tell me y, in the concept of stopping potential, when the polarity of the battery is reversed, the electrons are retarded ???
and
1. why is the stopped potential dependent on the metal?
2. why doesn't it depend on the intensity of light?
3. why does it depend on the frequency of light ?

finally one more question :-
A small plate of a metal(work function=1.17eV) is placed at a distance of 2m from a monchromatic light source of wavelength 4.8x10 power -7 and power 1.0 watt. the light falls normally on the plate.Find the number of photons striking the metal plate per square metre per second.

-ananya.

varshavallig

hi

for ur question about threshold frequency, yes if the frequency is greater than the threshold frequency only e will b emitted bcoz

h

- h

= 1/2mv²=K.E (

=threshold frequency)

if the given frequency is equal to the threshold frequency then the L.H.S of the eqn will become 0 i.e K.E will b 0. thus if the energy of the e is 0 it will not b emitted.thus

>

is the condition for the emission of e. (e=electron)

hope this helps u

if yes then plz rate me.

!!!!!!!!!

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