In a photoelectric effect experiment, electrons are ejected from a titanium surface (work function, 3 ev) following irradiation with uv light. the energy of the incident uv light is 7.2 x 10-19 j.
(a) calculate the wavelength of the ejected electrons.
(b) calculate the wavelength of the incident uv light.
(c) would an iron surface (ф-4.7 ev require a longer or shorter wavelength of light to eject electrons with the same wavelength calculated in part (a)? briefly explain.

Explanation:

According to the Einstein law, it is known that

where,   h = energy of light

            = work function

            = kinetic energy of electron

It is given that the value of is . And,

               1 eV =

Here,   for titanium is 4.33 eV

          = J  

          = J

(a)   First of all, kinetic energy will be calculated as follows.

                         = J

                         = J

It is known that mass of electrons is equal to .

Therefore,

and,    

                       =

                mv =

Now, the relation between wavelength and mv is as follows.

                   =

Therefore, the wavelength of the ejected electrons is .

(b)   It is known that relation between energy and wavelength is as follows.

               E =

                     =

                    =

Hence, the wavelength of the ejected electrons is .

(c)   For iron surface,

                                       = J

                                       = J

Here, the value of is more than the value of UV light source. Hence, we need a shorter wavelength light as we know that,

Therefore, lesser will be the wavelength higher will be the energy.