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Question

Statement 1: It was surprising for the scientist to observe that photocurrent depends on the frequency of the light.

Statement 2: According to the wave model , Energy of the light falling on the plate depends only on the amplitude of Light and not on frequency , so they assumed that changing frequency shouldn't change anything.


A

Statement 1 is true but statement 2 is not the correct reason for it

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B

statement 1 is true and statement 2 is the correct reason for it.

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C

Statement 1 and 2 both are false.

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D
Statement 1 is true but statement 2 is false.
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Solution

The correct option is B

statement 1 is true and statement 2 is the correct reason for it.


According to the classical theory of light , the only way for the photo current to increase is if the number of photo electrons emitted increases.

That we know can only happen if the rate at which energy is falling on the plate has increased.

One way of doing that was to keep the emitted plate closer to the source thereby increasing the intensity (energy per unit area per unit time)of light falling on the plate.

Other way is by changing the source and using one that radiates more energy or has higher power.

Basically these are the two ways of varying intensity of light falling.

The energy density of an E.M wave is given by

u(r,t)=12{ε0[E(r,t)]2+1μ0[B(r,t)]2}.

Here E and B are the amplitudes of electric and magnetic field. The energy radiated depends only on the amplitude of the fields and not on the frequency of the source. So thereby they had no reason to predict that by varying frequency or the colour of light, the energy falling on the plate will change anyhow.

That's why the surprise.


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