Chemistry, 18.10.2019 11:30 mayaleila

What is the kinetic energy of the emitted electrons when cesium is exposed to uv rays of frequency 1.3×1015hz?

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The kinetic energy of the emitted electrons of cesium when it is exposed to UV rays of frequency $1.3\times{10^{15}}\;{\text{Hz}}$ is $\boxed{8.614\times10^{-19}\text{ J}}$ .

Further Explanation:

Photoelectric effect:

When light is made to fall on any substance, electrons are emitted from it. This is known as the photoelectric effect and the emitted electrons are called photoelectrons. The electrons are emitted because of the transference of energy from light to the electrons.

Cesium is a member of the alkali metal group so it is highly reactive and shows the photoelectric effect to the maximum extent. It can remove its electron so easily because of its atomic size. Due to the large atomic size of cesium, its outermost electrons are held very less tightly to the nucleus and therefore removed easily.

According to the Planck-Einstein equation, the energy is proportional to the frequency and is expressed as follows:

${\text{E}}={\text{hv}}$ …… (1)

Here,

${\text{E}}$ is the energy.

is the Plank’s constant.

$\nu$ is the frequency.

The frequency of UV rays $1.3\times{10^{15}}\;{\text{Hz}}$ is or $1.3\times{10^{15}}\;{{\text{s}}^{-1}}$

The value of Planck’s constant is $6.626\times{10^{-34}}\;{\text{J}}\cdot{\text{s}}$ .

Substitute these values in equation (1)

$\begin{gathered}{\text{E}}=\left({6.626\times{{10}^{-34}}\;{\text{J}}\cdot{\text{s}}}\right)\left({1.3\times{{10}^{15}}\;{{\text{s}}^{-1}}}\right)\\= 8.614\times{10^{-19}}\;{\text{J}}\\\end{gathered}$

But when electrons are ejected out from the surface of the substance, all of its energy is considered as kinetic energy.

So the kinetic energy of the electrons is ${\mathbf{8}}{\mathbf{.614\times1}}{{\mathbf{0}}^{{\mathbf{-19}}}}\;{\mathbf{J}}$

Learn more:

1. Calculate the frequency of n = 6 in the Lyman series:

2. The energy of a photon in light:

Answer details:

Grade: Senior School

Subject: Chemistry

Chapter: Structure of the atom

Keywords: kinetic energy, frequency, energy, photoelectric effect, Planck's constant, light, electrons, photoelectrons, proportional, transference, reactive, cesium.

Answer from: Quest

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since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

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