Photoelectric Effect – Particle Nature of Light

Modern physics fully accepts the concept of wave-particle duality in case of light and other electromagnetic radiation. The phenomena such as interference, diffraction, and polarization can only be explained when light is treated as a wave whereas the phenomena such as the photoelectric effect, line spectra, and the production and scattering of x rays demonstrate the particle nature of light. In this article, in order to show the particle nature of light, I have discussed the photoelectric effect along with the necessary equations.

The photoelectric effect is defined as a phenomenon in which the emission of electrons occurs when a beam of light strikes a metal or a cathode surface. For the emission of electrons to take place, the frequency of incident light is required to be greater than a certain minimum value. This value is known as the threshold frequency. The threshold frequency depends on the metal or material of the cathode. For most of the metals, threshold frequency is in the ultraviolet range (wavelengths between 200 nm to 300 nm). If the intensity of light (I) is increased while keeping the frequency same, more electrons are emitted per unit time. Thus, photocurrent is directly proportional to the intensity of light.

The photoelectric effect was correctly explained by the world-famous physicist, Albert Einstein, in the year 1905. It is interesting to know that Einstein was awarded the Nobel Prize in Physics 1921 for his work on photoelectric effect. Einstein figured out that a beam of light comprises of small packages of energy known as photons or quanta. The energy of a photon (E) is equal to the product of the Planck’s constant (h) and the frequency of a photon (f). Frequency (f) of photon = speed of light (c)/wavelength of photon (λ).

The energy of a photon is given by –

E = hf = hc/λ

Planck’s constant (h) = 6.6260755(40) x 10-34

Photoelectric Effect - Particle Nature of Light by adidarwinian

A photon, present in a beam of light, is absorbed by an electron present at a cathode or metal surface. The electron gets all of the photon’s energy or none at all. If the energy absorbed by the electron is greater than the work function for that particular metal or cathode surface, the electron may escape from the surface. Work function (ϕ) for a surface is defined as the minimum amount of energy required by an individual electron in order to escape from that particular surface.

Applying the law of conservation of energy, Einstein stated that the maximum kinetic energy (Kmax) for an electron emitted from a surface (a photoelectron) can be calculated by subtracting the work function (ϕ) from the energy gained from a photon (hf).

Kmax = 1/2mv2max = hf – ϕ

m = mass of electron

vmax = maximum velocity attained by an emitted electron

The maximum kinetic energy (Kmax) of a photoelectron can also be measured as eV0

Kmax = eV0

e is the magnitude of electron charge and is = 1.602 x 10-19 C

The stopping potential (V0) is the potential required to stop the emission of an electron from the surface of a cathode towards the anode.

Thus, putting Kmax = eV0 we get the equation of photoelectric effect:

eV0 = hf – ϕ

For a given cathode material, work function (ϕ) is constant. As e and h are also constant, V0 turns out to be a linear function of the frequency f. A graph of V0 as a function of frequency (f) is a straight line. The above equation of photoelectric effect also show that greater the work function of a metal or material, the higher the minimum frequency of light required to induce photoelectric effect, i.e., to cause emission of electrons (photoelectrons).


    Along the Rivers – The Gallery Forests

    Along the Rivers – The Gallery Forests

    In this research paper, I have explored the gallery forests by clarifying the concept behind the term “gallery forest”, and studying their biogeography by reviewing some important ecoregions of North America and South America. I have discussed some of the notable gallery forests found in the Americas with respect to their geography, flora, and fauna. It is hoped that this paper will serve the interests of biologists, ecologists, botanists, zoologists, arborists, forest ecologists, biogeologists, biogeographists, and all other people including professionals, students, and laymen eager to learn about the gallery forests.

    A gallery forest is a narrow stretch or strip of forest along the banks of a water body, such as a river or stream, flowing through an otherwise open country. In the above context, an open country is defined as a region that is treeless or sparsely covered with trees. A gallery forest is also known as a fringing forest or riparian forest or riverine forest. Such forests are commonly found along the water bodies flowing through the savanna (or savannah) regions. The gallery forests are known to contain different types of woody vegetation. The width of a gallery forest may vary from several miles to complete absence along the same river.
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      A Glance into the Human Brain

      A Glance into the Human Brain – Structure and Functions of the Human Brain (Human Brain’s Anatomy and Physiology) – A Voyage Into the Human Brain!

      This article describes the structure of human brain (anatomy of human brain) and functions of human brain (physiology of human brain), which is the most complex and mysterious organ of the human body. This article is expected to cater the needs of a variety of audiences including the students, teachers, healthcare professionals, and the laymen. The article has been written in an easy-to-understand language and richly annotated with definitions of difficult medical terms including etymologies.

      The human brain is the most sophisticated organ of the human body, and can aptly be called as a biological marvel. The brain and the spinal cord constitute the central nervous system (CNS). The brain plays the role of the control tower or control center of the human body, and relies on a vast network of nerves (bundles of fibers of nervous tissue carrying impulses) spread throughout the body. Nerves can be compared to the electrical wiring as they carry electrical impulses.

      Noteworthy Facts about the Human Brain!

      • The brain of human beings resembles a small cauliflower in its size and appearance.
      • Human brain is comprised of about 100 billion neurons or nerve cells.
      • The weight of an adult human brain is about 1300 g (about 3 pounds), whereas the weight of a newborn’s brain lies in the range of 350 – 400 g.
      • Although the brain of a human being accounts for only 2 % of the total body weight, it utilizes 20 % of the of the resting total body oxygen consumption.
      • Human brain contains 77 to 78 % water, 10 to 12 % lipids, 8 % proteins, 2 % soluble organic substances, 1 % carbohydrates, and 1 % inorganic salts.
      • The cerebral cortex forms 77% by volume of the human brain.
      • Cerebrum is the largest part of the human brain, whereas Cerebellum is the second largest.
      • Left side of the brain (left cerebral hemisphere) controls the right side of the body, whereas the right side of the brain (right cerebral hemisphere) controls the left side of the human body.

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        Seahorses in Traditional Chinese Medicine (TCM)

        Seahorses are magnificent fishes that exhibit the phenomenon of male pregnancy. Pregnancy in males is unique to seahorses in the entire animal kingdom, thus, making them a true biological marvel. This exclusive behavior was discussed in detail in my research article titled “Seahorse – Male Endurance – Roles Swapped!!” Here, in this new research paper / article, I shall explore the use of seahorses in Traditional Chinese Medicine (TCM).

        Seahorses are globally exploited for use as aquarium fishes, curios (articles or objects of curiosity), medicines, and even foods. Use of Seahorses in Traditional Chinese Medicine (TCM) was first mentioned in the book named “Bencao Shiyi” (Supplement to Materia Medica), written by Chen Cangqi around 720 A.D.

        Seahorses are used in the treatment of a wide range of health problems under the Traditional Chinese Medicine (TCM), which is a complementary and alternative system of medicine (CAM). You can refer to my article – “The Basis of Traditional Chinese Medicine (TCM)” to learn the fundamentals of TCM. Seahorses are employed in the treatment of sexual weakness, reduced sexual desire or drive (reduced libido; libido means sexual desire or sex drive), and are considered as broad-spectrum or general tonics. The practitioners of TCM claim that seahorses strengthen “kidneys” and improve “nerves”, which in the context of Traditional Chinese Medicine points to general morale, well-being, and vigor. “kidneys” also imply sexual function in the context of TCM. Seahorses are categorized under sweet, salty, and warm medicines. They are usually not prescribed alone but in combo-preparations (formulations containing multiple ingredients) containing matter from other animals and plants.

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