1.Photons are elementary particles, which means they cannot be divided into smaller particles.
2.They have zero rest mass, meaning that they always travel at the speed of light in a vacuum.
3. Photons have both wave-like and particle-like properties. They behave like waves when they interact with matter, and like particles when they are detected.
4.The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength, as given by the equation E = hf, where E is the energy, h is Planck's constant, and f is the frequency.
5.The momentum of a photon is given by p = h/λ, where p is the momentum, h is Planck's constant, and λ is the wavelength.
6.Photons are electrically neutral, which means they do not have an electric charge.
7.Photons always travel at the speed of light, regardless of their energy or wavelength.
8.Photons can be created and destroyed, but the total number of photons in a closed system is always conserved.
Milikan's photoelectric experiment was set up to verify the Einstein photoelectric effect equation and to determine the value of Plank's constant. The experimental set-up consists of a glass tube with a rotating wheel coated with alkali metals acting as cathode and a cup-shaped anode connected through a variable battery and electrometers. A knife is used to remove metal oxide from the cathode, and light is allowed to fall on the cathode through a window. The emitted photoelectrons move towards the anode, resulting in a photocurrent in the electrometer 'E.'
As the negative potential at the anode increases, the photocurrent decreases, and a particular value of negative potential is called stopping potential, denoted by Vs. Milikan's experiment involves observing the stopping potential for different frequencies of light. By plotting Vs versus f, if the equation is a straight line of the form y = mx + c, where slope m = h/e and intercept c = -hf0/e, then Einstein's photoelectric equation is verified.
The slope of the graph is given by m = b/a, where b is the change in stopping potential and a is the change in frequency. From equation (ii), h = (b/a) * e. Thus, the value of Plank's constant can be determined knowing the values of a, b, and e. The value of Plank's constant was found to be 6.62 * 10^-34J/s.
The photoelectric effect is the phenomenon in which electrons are emitted from a material surface when light falls on it. This effect is explained by the quantum theory of radiation proposed by Albert Einstein. The energy of light is quantized into particles called photons. When a photon of light falls on a metal surface, it can eject an electron from the metal if the energy of the photon is greater than the work function of the metal.
The work function of a metal is defined as the minimum amount of energy required to remove an electron from the metal surface. If the energy of the photon is less than the work function of the metal, no electron will be ejected. The maximum kinetic energy of the emitted electrons is given by the difference between the energy of the photon and the work function of the metal.
The photoelectric effect has several practical applications. For example, it is used in photoelectric cells to convert light energy into electrical energy. These cells are used in various electronic devices such as calculators, digital clocks, and solar panels. Photoelectric effect is also used in the measurement of small amounts of light intensity, as in the case of photomultipliers used in particle physics experiments.
The photoelectric effect has a significant impact on our understanding of the nature of light and matter. It provided the first experimental evidence for the particle-like nature of light, which was initially proposed by Albert Einstein. This effect also played a crucial role in the development of the concept of wave-particle duality, which suggests that all matter and energy have both wave-like and particle-like properties.
The photoelectric effect has also been used to study the electronic properties of solids. By measuring the kinetic energy and direction of the emitted electrons, it is possible to determine the momentum and energy of the electrons in the solid. This information can be used to study the electronic structure and properties of solids, such as their conductivity and optical properties.
In conclusion, the photoelectric effect is an important phenomenon in physics that has contributed significantly to our understanding of the nature of light and matter. Its practical applications in various fields of science and technology make it a crucial topic of study for students and researchers alike.
To determine the value of Plank's constant and verify the photoelectric effect equation, Milikan conducted an experiment known as Milikan's photoelectric experiment. The experimental setup consisted of a glass tube with a rotating wheel at the center, where alkali metals were coated. These metals acted as a cathode, and a cup-shaped anode was present. The electrodes were connected through a variable battery and electrometers. A knife was used to remove any metal oxide that might have formed on the cathode. A window was provided for the light to pass through the tube.
In the experiment, light was allowed to fall on the cathode, and photoelectrons were emitted and moved towards the anode due to the potential difference between them. This movement was observed as photon current in the electrometer E. The negative potential was then increased at the anode, which caused a decrease in the photocurrent. The potential difference at which the photocurrent became zero was called the stopping potential, denoted by Vs.
Using Einstein's photoelectric equation, we can write E = θ + K.E.max, where E is the energy of the photon, θ is the threshold energy, and K.E.max is the maximum kinetic energy of the emitted photoelectron.
Therefore, hf = hfo + eVs, where f is the frequency of the light, h is Planck's constant, e is the electronic charge, and f0 is the threshold frequency.
We can rewrite this equation as Vs = (h/e)f - (h/e)f0, which is a straight line of the form y = mx + c, where the slope m is h/e, and the intercept c is -(hf0)/e. By plotting Vs versus f and verifying that the plot is a straight line, we can confirm Einstein's photoelectric effect equation.
The slope of the experimental result from the graph gives the value of h/e. Therefore, we can calculate Planck's constant by knowing the values of a, b, and e in the expression h = (b/a) * e. Milikan's experiment determined the value of Planck's constant to be 6.626 x 10^-34 J s.
By aswin aryal