Aj photon of waveelngth `3,310 overset @A` falls ion a photocathode and an electron of energy `3 xx 10^(-19) J` is ejected.If the waveelngth of the incident photos is changed to `5,000 overset @A`,the energy of the ejected electron is `0.972 xx 10^(-19) J`.Claulate the value of Planck's constant and threshold waveelngth of the photocathode.Given the velocity of light `= 3 xx 10^8 m s^(-1)`.