First slide

Photo Electric Effect

Question

In a photo electric experiment when light of intensity I and wavelength $λ$ is used, saturated current is found to be 10 mA. In the same experimental set up, when light of intensity I and wavelength $λ / 2$ is used, saturation current is found to be i. Then

Easy

A

$i = 10 m A$
B

$i > 10 m A$
C

$i < 10 m A$
D

with the given informations it is not possible to find the relation between i and 10 mA.

Solution

If numbers of photons passing through unit cross sectional area in unit time is n, then intensity $I = h ν . n = h c n / λ$
when wavelength is halved, $I = h c n^{1} / (λ / 2) = \frac{2 h c n^{1}}{λ}$
$∴ n^{1} = \frac{n}{2}$ . So number of photo electrons ejected in unit time is reduced and hence $i < 10 m A$ .

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