Question

A surface ejects electrons when hitted with green light but not. When hitted by yellow light. Will electron be ejected if the surfaces is hit by red light:
(A) Yes
(B) No
(C) Yes, if the red beam is quite intense
(D) Yes, if the red beam is continuous to fall upon the surface for a long time.

Answer 1

Hint: To answer this question, we should know about photoelectron emission. Depending on the magnitude of the shorter wave or longer wave the wavelength of a particular wave is decided. For example the blue light has a shorter wave, hence the wavelength is also less. This may help apparently to answer this question within no time.

Complete answer:
When the beam of the light falls on a surface of the metals like sodium, potassium, caesium and rubidium. Firstly the electrons absorb while exiting to a higher state. The electrons start emitting back when the electrons come back from excited state to ground state. This phenomenon of emission of electrons is known as the photoelectric emission.
The intensity of incident photons is equal to the intensity of emitted light.
The energy of photons incident on the surface depends on the frequency of the light and is expressed as,
E $\propto$ $\dfrac{1}{\lambda }$
where, E = energy
$\lambda$ = Wavelength
When the electrons emits from a material that has absorbed the electromagnetic radiation is known as photoelectric effect.
With increase in wavelength, the photoelectric effect does not occur.
The answer is option B, that is "no" as the wavelength of red light is higher when compared to yellow or blue light.
\[{{\lambda }_{red}} > {{\lambda }_{yellow}} > {{\lambda }_{green}}\]
Yellow light has lesser wavelength than red. In the question it is mentioned that the surface won't eject electrons when yellow light hits. So, red having higher wavelength won't eject back .

Thus option B is the correct answer.

Note:
We can answer this question within no time if we know the wavelength order. The trick used to remember the order is VIBGYOR. This exactly goes for concentration too. If the intensity is more also no matter as there is no relation between wavelengths. Wavelength is inversely dependent on the energy of the light and directly depends on the magnitude of wavelength.