Question

characteristic of Photoelectric effect

Answer 1

i) Effect of Intensity : Intensity of light means the energy incident per unit area per second. For a given frequency, if intensity of incident light is increased, the photoelectric current increases and with decrease of intensity, the photoelectric current decreases; but the stopping potential remains the same.
(ii) Effect of Frequency : When the intensity of incident light is kept fixed and frequency is increased, the photoelectric current remains the same; but the stopping potential increases.

If the frequency is decreased, the stopping potential decreases and at a particular frequency of incident light, the stopping potential becomes zero. This value of frequency of incident light for which the stopping potential is zero is called threshold frequency ν0If the frequency of incident light (ν) is less than the threshold frequency (ν0), no photoelectric emission takes place.

Thus, the increase of frequency increases the maximum kinetic energy of photoelectrons but leaves the photoelectric current unchanged.


(iii) Effect of Photometal : When frequency and intensity of incident light are kept fixed and photometal is changed, we observe that stopping potentials (Vs) versus frequency (v) graphs are parallel straight lines, cutting frequency axis at different points (Fig). This shows that threshold frequencies are different for different metals, the slope (Vs/ν) for all the metals is same and hence a universal constant.

(iv) Effect of Time : There is no time lag between the incidence of light and the emission of photoelectrons.

Answer 2

1....if wave front carry energy than a large no of electrons should be ejected together .
2...if the frequency is less than threshold frequentcy than electron is not emitted what ever it's intensity or amplitude.
3...there is no time gap in light and ejection of electron due to wave front