Question

This is an apparatus for studying the photoelectric effect. The work function of the material beinginvestigated is 3.810–19J. Light of a wavelength 350 nm is incident on the material. What is the lowestvoltage needed between the cathode (C) and the anode (A) to stop any electrons ejected from the cathodefrom reaching the anode?

Answer 1

Answer:

1.175 V

Explanation:

We are given that

Work function of the material=$w_0=3.8\times 10^{-19}$ J

Wavelength of light=$350 nm=350\times 10^{-9}$m

$1nm=10^{-9} m$

Energy of photon=Work function+Kinetic energy of electron

$\frac{hc}{\lambda}=w_0+e\delta V$

Where

$\lambda$=Wavelength of light

$c=3\times 10^8 m/s$=Speed of light

$w_0=$Work function

$\delta V$=Small voltage

$h=6.63\times 10^{-34} J-s$=Plank's constant

$e=1.6\times 10^{-19} C$

Substitute the values then we get

$\frac{6.63\times 10^{-34}\times 3\times 10^8}{350\times 10^{-9}}=3.8\times 10^{-19}+1.6\times 10^{-19}\delta V$

$5.68\times 10^{-19}-3.8\times 10^{-19}=1.6\times 10^{-19}\delta V$

$1.88\times 10^{-19}=1.6\times 10^{-19}\delta V$

$\delat V=\frac{1.88\times 10^{-19}}{1.6\times 10^{-19}}$

$\delta V=1.175 V$

Hence, the lowest voltage needed between the cathode and the anode to stop any electrons ejected from the cathode from reaching the anode=1.175 V