Question

3. What is photoelectric effect? Explain details threshold frequency, and stopping potentials? Sketch the diagram and necessary formula? Problem-3: What is the threshold wavelength of electron generated by 200 V?

Answer 1

Photoelectric Effect: The ejection of electrons from a material by the action of light is called the photoelectric effect. The emitted electrons are called photoelectrons.

Most metallic surfaces show photoelectric effect with ultraviolet light.

Stopping Potential: Stopping potential is defined as the potential required to stop any electron from reaching other side.

In other words, stopping potential is that potential at which photoelectric current becomes zero.

Threshold Frequency: There exists a minimum frequency at which the stopping potential becomes zero. This means that no electrons are emitted if frequency of incident light is below that minimum frequency. This minimum frequency is known as threshold frequency.

This graph shows the relation between stopping potential and frequency. Threshold frequency is also marked.

Photoelectric Effect: The ejection of electrons from a material by the action of light is called the photoelectric effect. The emitted electrons are called photo electrons. Most metallic surfaces show photoelectric effect with ultraviolet light. Stopping Potential: Stopping potential is defined as the potential required to stop any electron from reaching other side. In other words, stopping potential is that potential at which photoelectric current becomes zero. Threshold Frequency: There exists a minimum frequency at which the stopping potential becomes zero. This means that no electrons are emitted if frequency of incident light is below that minimum frequency. This minimum frequency is known as threshold frequency. This graph shows the relation between stopping potential and frequency. Threshold frequency is also marked. This shows that stopping potential linearly increases with frequency. * Stopping potential can be calculated using formula, e V_0 = 1/2 mv^2_max where e is electron charge, V????? ?o is stopping potential and v_max is the maximum velocity

This shows that stopping potential linearly increases with frequency.

* Stopping potential can be calculated using formula,  $eV_{o} = \frac{1}{2}mv_{max}^{2}$ where e is electron charge, V_{​​​​​​o} is stopping potential and v_max is the maximum velocity of ejected electron.

* Threshold frequency depends on the metal used in photocathode.

Threshold Wavelength: Threshold wavelength of electron can be calculated using the formula $\lambda = \frac{h}{\sqrt{2meV}}$ where h is Planck's constant, m is mass of electron, e is electron charge and V is the potential.

$\lambda = \frac{6.63 * 10^{-34}}{\sqrt{2*9.1*10^{-31}*1.6*10^{-19}*200}} = 0.868 * 10^{-10} m$