SEM & TEM, Periscope & Pyrometer, Perimeter & Altimeter, Pelage & Plumage

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  • SEM involves shooting an electron beam at a specimen and observing the reactions on the specimen surface. When the electron hits a molecule on the surface, its energy is absorbed by the molecule, which in turn emits a lower amount of energy.

  • This energy can be in the form of a secondary, less energetic electron, a photon of light, or x-rays. Differentiation between these emissions is used to produce image contrast.

  • However, in order to produce a coherent image, the sample must often be prepared with a conductive coating or by embedding a resin for many biological samples.


  • TEM acts much like a typical bright field microscope in the sense that it sends electrons through a specimen. As it propagates through the specimen, some of the electrons are scattered and some are transmitted.

  • The transmitted electrons is passed through an objective lens and then projected onto a scintillating material which can then be recorded photographically.

  • This requires samples to be prepared in very thin slices in order to allow transmission of the electrons through transparent sections.


  • A SEM (scanning electron microscope) images using the electrons reflected from a specimen. A TEM (transmission electron microscope) images using the electrons that pass through it.

  • The image from an SEM thus looks somewhat like a normal photo (we’re used to imaging using the light reflected from objects). However, a TEM image takes a bit more interpretation as we’re not used to seeing images of light that’s passed through things - think of silhouettes or slide projectors.

Periscope & Pyrometer

Periscope: Instrument used by submarines to see above the surface of the sea.

Pyrometer: Instrument used for measuring high temperatures.

Cell & Battery

Cell: A cell is a DC voltage source in which chemical energy is converted into electricity.

Battery: It is a device which produces electricity through the use of acid and other chemicals. It is assembly of many cells.

Perimeter & Altimeter


A perimeter is a path that surrounds an area. The word comes from the Greek Peri (around) and meter (measure). The term may be used either for the path or its length - it can be thought of as the length of the outline of a shape. The perimeter of a circular area is called circumference.


An altimeter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.

Pelage & Plumage


It is a growth of hair/fur/wool covering the skin of animals.


Plumages are feathers covering the body of birds.

Smog & Smoke

Smog Smog is formed by the interaction of pollutants present in the air in presence of sun light (photochemical smog), it usually restricts visibility and is hazardous to health.

Smoke: Smoke is the thin fine particles usually result from the combustion.

Radiotherapy & Chemotherapy

  • Â Radiation targets only the cancer cells. However, chemotherapy is administered through the blood and therefore, affects both cancerous and non-cancerous cells

  • Though they can be used for any sort of cancer, radiation mainly targets solid tumours like those of the cervix, spine and skin.

  • Chemotherapy treats cancers through medicines, while radiation deals with cancer cells through rays

  • Radiation results in additional side effects like internal inflammation, especially in the stomach and the intestine.

Springtides & Neap Tides


  • Spring Tides When the moon is full or new, the gravitational pull of the moon and sun are combined.

  • At these times, the high tides are very high and the low tides are very low. This is known as a spring high tide.

  • Spring tides are especially strong tides (they do not have anything to do with the season spring).

  • They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides.

  • Spring tides occur during the full moon and the new moon.

Neap Tides

  • Neap Tides During the moon’s quarter phases the sun and moon work at right angles, causing the bulges to cancel each other.

  • The result is a smaller difference between high and low tides and is known as a neap tide.

  • Neap tides are especially weak tides.

  • They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth).

  • Neap tides occur during quarter moon.

Vertebrates & Invertebrates

  • Vertebrates have a backbone with a spinal cord, whereas invertebrates do not.

  • The diversity is exceptionally high among the invertebrates compared to vertebrates.

  • Vertebrates are always bilaterally symmetrical, while invertebrates could show either bilateral or radial symmetry.

  • Vertebrates are usually large-bodied and move fast compared to invertebrates.

  • Vertebrates have a closed blood system, a well-developed brain, either gills or lungs for respiration, and a complex and sophisticated nervous system, whereas those are primitive in invertebrates. Therefore, it concerns that vertebrates have many specializations to extract the best out of the environment compared to invertebrates.

Fluorescent & Neon Light

  • A neon light is the sort of light you see used in advertising signs. These signs are made of long, narrow glass tubes, and these tubes are often bent into all sorts of shapes. The tube of a neon light can spell out a word, for example. These tubes emit light in different colours.

  • A fluorescent light, on the other hand, is most often a long, straight tube that produces white light. You see fluorescent lights in offices, stores and some home fixtures.

  • The idea behind a neon light is simple. Inside the glass tube there is a gas like neon, argon or krypton at low pressure. At both ends of the tube there are metal electrodes. When you apply a high voltage to the electrodes, the neon gas ionizes, and electrons flow through the gas. These electrons excite the neon atoms and cause them to emit light that we can see. Neon emits red light when energized in this way. Other gases emit other colours.

  • A fluorescent light works on a similar idea but it has an extra step. Inside a fluorescent light is low-pressure mercury vapour. When ionized, mercury vapour emits ultraviolet light. Human eyes are not sensitive to ultraviolet light (although human skin is -- see How Sunburns and Sun Tans Work!). Therefore, the inside of a fluorescent light is coated with a phosphor. A phosphor is a substance that can accept energy in one form (for example, energy from a high-speed electron as in a TV tube -- see How Television Works) and emit the energy in the form of visible light. In a fluorescent lamp, the phosphor accepts the energy of ultraviolet photons and emits visible photons.

  • The light we see from a fluorescent tube is the light given off by the phosphor that coats the inside of the tube (the phosphor fluoresces when energized, hence the name). The light of a neon tube is the colored light that the neon atoms give off directly.

  • Telemeter: A telemeter is a device used to remotely measure a quantity. Telemeters are generally the physical devices used in telemetry. Electronic devices are widely used in telemetry and can be wireless or hard-wired, analogue or digital. Other technologies are possible, however, such as mechanical, hydraulic and optical.

  • Multimeter: A multimeter or a multi-tester, also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. Multimeters may use analogue or digital circuits—analogue Multimeters (AMM) and digital Multimeters (often abbreviated DMM or DVOM.)

  • Analog instruments are usually based on a micro-ammeter whose pointer moves over a scale calibrated for all the different measurements that can be made; digital instruments usually display digits, but may display a bar of a length proportional to the quantity being measured.

  • A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.

Periscope and Microscope


  • A periscope is an instrument for observation from a concealed position. In its simplest form it consists of a tube with mirrors at each end set parallel to each other at a 45-degree angle. This form of periscope, with the addition of two simple lenses, served for observation purposes in the trenches during World War I. Military personnel also use periscopes in some gun turrets and in armoured vehicles.

  • More complex periscopes, using prisms instead of mirrors, and providing magnification, operate on submarines. The overall design of the classical submarine periscope is very simple: two telescopes pointed into each other. If the two telescopes have different individual magnification, the difference between them causes an overall magnification or reduction.


  • A microscope (from the Greek: μικρός, micros, “small” and σκοπεῖν, spoken, “to look” or “see”) is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy. Microscopic means invisible to the eye unless aided by a microscope.

  • There are many types of microscopes, the most common and first to be invented is the optical microscope which uses light to image the sample. Other major types of microscopes are the electron microscope (both the transmission electron microscope and the scanning electron microscope) and the various types of scanning probe microscope.

Nucleon and Photon


  • A nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles. Now they are known to be composite particles, each made of three quarks bound together by the so-called strong interaction.

  • The interaction between two or more nucleons is called inter-nucleon interactions or nuclear force, which is also ultimately caused by the strong interaction. (Before the discovery of quarks, the term “strong interaction” referred to just inter-nucleon interactions.)


  • A photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the photon has no rest mass; this allows for interactions at long distances.

  • Like all elementary particles, photons are currently best explained by quantum mechanics and will exhibit wave–particle duality, exhibiting properties of both waves and particles.

  • For example, a single photon may be refracted by a lens or exhibit wave interference with itself, but also act as a particle giving a definite result when quantitative momentum (quantized angular momentum) is measured.