Fast medium

Light travels through different media such as air, glass or water at different speeds.  A fast medium is one through which it passes through more quickly than others.

  • Light travels through a vacuum at 299,792 kilometres per second.
  • Light travels through other media at lower speeds.
  • In some cases, it travels at a speed which is near the speed of light (the speed at which light travels through a vacuum) and in other cases, it travels much more slowly.
  • It is useful to know whether a medium is fast or slow to predict what will happen when light crosses the boundary between one medium and another. So:
    • If light crosses the boundary from a medium in which it travels fast into a material in which it travels more slowly, then it will bend towards the normal.
    • If light crosses the boundary from a medium in which it travels slowly into a material in which it travels more quickly, then the light ray will bend away from the normal.
  • In optics, the normal is a line drawn in a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.

Light travels through different media such as air, glass or water at different speeds.  A fast medium is one through which it passes through more quickly than others.

  • Light travels through a vacuum at 299,792 kilometres per second.
  • Light travels through other media at lower speeds.
  • In some cases, it travels at a speed which is near the speed of light (the speed at which light travels through a vacuum) and in other cases, it travels much more slowly.
  • It is useful to know whether a medium is fast or slow to predict what will happen when light crosses the boundary between one medium and another.
  • so:
  • If light crosses the boundary from a medium in which it travels fast into a material in which it travels more slowly, then it will bend towards the normal.
  • If light crosses the boundary from a medium in which it travels slowly into a material in which it travels more quickly, then the light ray will bend away from the normal.
  • In optics, the normal is a line drawn in a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.

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Fast medium

Light travels through different media such as air, glass or water at different speeds.  A fast medium is one through which it passes through more quickly than others.

  • Light travels through a vacuum at 299,792 kilometres per second.
  • Light travels through other media at lower speeds.
  • In some cases, it travels at a speed which is near the speed of light (the speed at which light travels through a vacuum) and in other cases, it travels much more slowly.
  • It is useful to know whether a medium is fast or slow to predict what will happen when light crosses the boundary between one medium and another.
  • so:
  • If light crosses the boundary from a medium in which it travels fast into a material in which it travels more slowly, then it will bend towards the normal.
  • If light crosses the boundary from a medium in which it travels slowly into a material in which it travels more quickly, then the light ray will bend away from the normal.
  • In optics, the normal is a line drawn in a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.

Fog bows, dew bows and more

There are many optical effects similar to rainbows.

  • A fog bow is a similar phenomenon to a rainbow. As its name suggests, it is associated with fog rather than rain. Because of the very small size of water droplets that cause fog, a fog bow has only very weak colours.
  • A dew bow can form where dewdrops reflect and disperse sunlight. Dew bows can sometimes be seen on fields in the early morning when the temperature drops below the dew point during the night, moisture in the air condenses, falls to the ground, and covers cobwebs.
  • A moon bow is produced by moonlight rather than sunlight but appears for the same reasons. Moon bows are often too faint to excite the colour receptors (cone cells) of a human eye but can appear in photographs taken at night with a long exposure.
  • A twinned rainbow is produced when two rain showers with different sized raindrops overlap one another. Each rainbow has red on the outside and violet on the inside. The two bows often intersect at one end.
  • A reflection rainbow is produced when strong sunlight reflects off a large lake or the ocean before striking a curtain of rain. The conditions must be ideal if the reflecting water is to act as a mirror. A reflected rainbow appears to be similar to a primary bow but has a higher arc. Don’t get confused between a reflection rainbow that appears in the sky and a rainbow reflected in water.
  • A glory is a circle of bright white light that appears around the anti-solar point.
  • A halo is a circle of bright multicoloured light caused by ice crystals that appears around the Sun or the Moon.
  • A monochrome rainbow only occurs when the Sun is on the horizon. When an observer sees a sunrise or sunset, light is travelling horizontally through the atmosphere for several hundred kilometres. In the process, atmospheric conditions cause all but the longest wavelengths to scatter so the Sun appears to be a diffuse orange/red oval. Because all other wavelengths are absent from a monochrome rainbow, the whole scene may appear to be tinged with a fire-like glow.

Force

In physics, a force is an influence that can change the motion of an object. Forces bind things together and push things apart.

  • The push-pull interactions between things are described as the interplay of forces.
  • Forces explain how anything interacts with anything else in the whole of the natural world.
  • Forces produce motion and can cause an object with mass to change velocity.
  • Changes in velocity include causing things to start moving from a state of rest, to accelerate or slow down.
  • Quarks and leptons, fundamental particles present in all forms of matter, are bound together by fundamental forces.
  • There are four fundamental forces that account for all the forms of pulling and pushing between things in the Universe.

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Fovea

The entire surface of the retina contains nerve cells, but there is a small portion with a diameter of approximately 0.25 mm at the centre of the macula called the fovea centralis where the concentration of cones is greatest.

  • This region is the optimal location for the formation of image detail.
  • The eyes constantly rotate in their sockets to focus images of objects of interest as precisely as possible at this location.

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Fovea centralis

Fovea centralis

The entire surface of the retina contains nerve cells, but there is a small portion with a diameter of approximately 0.25 mm at the centre of the macula called the fovea centralis where the concentration of cones is greatest. This region is the optimal location for the formation of image detail. The eyes constantly rotate in their sockets to focus images of objects of interest as precisely as possible at this location.

Frequency

The frequency of electromagnetic radiation (light) refers to the number of wave-cycles of an electromagnetic wave that pass a given point in a given amount of time.

  • The frequency of a wave should not be confused with the speed at which the wave travels or the distance it travels.
  • The term frequency refers to the measurement of the frequency of wave-cycles that pass a given point in a given amount of time.
  • Frequency is measured in Hertz (Hz). One Hertz is one wave-cycle per second.
  • The wavelength and frequency of light are closely related. the higher the frequency, the shorter the wavelength.
  • The amount of energy transported by a light wave increases with the frequency of oscillations and as the length of each oscillation decreases.

The frequency of electromagnetic radiation (light) refers to the number of wave-cycles of an electromagnetic wave that pass a given point in a given amount of time.

Fundamental force

In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions.

The four fundamental forces that account for all the forms of pulling and pushing between things are:

  • Gravitational force: Gravity is the phenomenon that causes things with mass or energy to gravitate towards one another. Planets, stars, galaxies, and even light are all affected by gravity. The effect of gravity on small things like human beings when in the vicinity of something big like a planet is obvious. It is the Moon’s gravity that causes ocean tides on Earth. Gravity accounts for physical objects having weight. Gravity has an infinite range, although its effects become weaker as objects get further away from one another.
  • Weak Nuclear force: In nuclear physics and particle physics, the weak nuclear force explains the interaction between subatomic particles that is responsible for the radioactive decay of atoms. The weak nuclear force doesn’t affect electromagnetic radiation.
  • Strong Nuclear force: The strong nuclear force holds matter together. It binds the sub-atomic particles, protons and neutrons, that form the nucleus of an atom. Whilst repulsive electromagnetic forces push them apart, the attractive nuclear force is strong enough to overcome them at short range. The range at work here is measured in femtometres. The nuclear force plays an essential role in storing energy that is used in nuclear power and nuclear weapons.
  • Electromagnetic force: The electromagnetic force is the force that occurs between electrically charged particles, such as electrons, and is described as either a positive or negative charge. Objects with opposite charges produce an attractive force between them, while objects with the same charge produce a repulsive force. The electromagnetic force is carried by photons in the form of electric and magnetic fields that propagate at the speed of light.
  • Whenever there is a push-pull interaction between two objects, forces are applied to each of them. When the interaction ceases, the two objects no longer experience the force and their momentum continues uninterrupted.
  • On a macro-scale wherever there is a concentration of stuff, in planets, suns or galaxies for example, that is where massive push-pulls happen.
  • Everything everywhere is in motion. Nothing in the whole Universe is stationary unless its temperature is reduced to absolute zero. But in reality nothing can be cooled to a temperature of exactly absolute zero.
  • Motion applies to everything including objects, bodies, matter, particles, radiation and space-time. We also refer to the motion of images, shapes and boundaries.
  • Motion signifies a change in the position of the elements of a physical system. But an object’s motion (its momentum) stays the same unless a force acts on it.

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