Question

Different wavelengths of electromagnetic radiation were directed onto tow different metal samples (see picture). Scientists then recorded if any particles were ejected and if so what type of particles as well as the speed of the particle. What patterns do you see in the results that were collected? Exp Wavelength of Light Directed al Sample Intensity Where Particles Elected Elected Particle speed of Elected Particle 4.9x104 5.4x107m 3.3x10m Medium Hich 3.510 2.0 m N/A N/A 3.3 100m High Low Medium High 28 2 3.510 Electromagnetic Radiation N/A N/A Elected 2.0 m 6.11012m 2.7 109 5.5x10m High N/A N/A Wavelength of Light Directed at Sample Where Particles Ejected No Elected Particle Particle N/A Yes NO N/A 5.4*10' m 3.410 m 3.9x109 m 2.4x10 m 3.9x10m 2.6*10'm 3.4 101 m Medium High Medium High Low Low Low Speed of Ejected Particle N/A 1.1 10° N/A 4.1 10° N/A 1.1X105 1.1*10' Yes No N/A Yes

Answer 1

In the above mentioned results, it is observed that every metal requires a minimum threshold energy equal to or above which electrons can be ejected from the surface of the metal.

The relation between wavelength and energy is shown below:

$E=\dfrac{hc}{\lambda}$

Therefore, at low values of wavelength energy increases. Higher is the energy, easier is it for the electrons to be ejected and the speed of electrons further increases.

For example, in case of Potassium if the wavelength was 2 m the energy is very less and is insufficient for the ejection of electrons. On decreasing the wavelength, energy increases and ejection of electron is possible.

Similarly, in case of iron if the wavelength was $3.9\times 10^{3} \; \rm{m}$ , then ejection of electron was not possible as energy was extremely low.

Whereas on decreasing the wavelength the energy increased and ejection of electron was possible.

Also, the intensity of light has no effect on the ejection of electron. This concludes that the speed of electron with the electron is ejected is solely dependent on the energy.

This effect is also known as the PHOTOELECTRIC EFFECT.