Dictionary tag: O

Object

An object is a physical entity and so a thing that has mass and occupies space.

  • Objects can be described based on their properties such as size, shape, texture, and colour.
  • The perception of an object is a result of the brain’s interpretation of sensory information received from the physical entity.
  • All objects are composed of atoms or molecules, which are the building blocks of matter.
  • The properties of the atoms and molecules that make up an object determine its physical and chemical properties.
Is a rainbow an object?
About the colour of objects
  • Objects are composed of atoms, which bond together to form molecules, elements, and compounds. These different combinations of atoms give objects their unique properties and determine how they react to light.
  • Objects appear to have different colours because they absorb some wavelengths of light and reflect or transmit others. The wavelengths that are reflected determine the colour of an object seen by an observer.
  • In physics, the absorption and reflection of light are explained as follows:
      • Atoms are composed of protons, neutrons and electrons. Protons and neutrons form the nucleus and electrons orbit the nucleus.
      • The orbit, or energy level, of an electron in an atom can change when the electron gains or loses energy.
      • When an electron absorbs a photon of light, it gains energy and moves to a higher energy level so a higher orbit.
      • The difference between the initial and final energy levels of the electron is equal to the energy of the absorbed photon.
      • When an electron moves to a higher energy level it is in an unstable state and eventually returns to its original lower energy level.
      • When the electron returns to its original lower energy level, it emits a photon of light with a frequency and wavelength corresponding to the energy difference between the two levels.
      • The difference between any two energy levels of an electron is specific to the type of atom and can be thought of as being equal to a “quantum” of energy,  where a quantum is understood to mean an indivisible unit of energy.
      • Every type of atom has a unique set of energy levels, and so it emits or absorbs photons of light at specific wavelengths or colours.
    • The colour of objects perceived by an observer can be affected by the lighting conditions in which they are viewed and so by the spectral power distribution of the light source.
    • The surface texture of objects affects how light interacts with them. Smooth and polished surfaces reflect light in a regular pattern, while rough and textured surfaces scatter light and colour in many directions.
    • Transparent objects allow much of the light that strikes them to pass through. The colour seen by an observer is affected by impurities or defects in the material and by the colour of the background against which they are viewed.
    • In the case of opaque objects, the surface of the object reflects, absorbs or scatters light, which determines what is seen by the observer.
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References

An object is a material thing that can be seen and touched.

  • An object is intuitively assumed to exist and to be responsible for a unified experience, consisting of visual and other sensations and perceptions.
  • Every object, material, medium or substance that we can see is made of matter of one kind or another. The key differentiating factor is the elements and molecules they are constructed from.
  • You will have come across the elements that make up the periodic table.
  • A close look at molecules reveals that they are made up of atoms composed of electrons surrounding a nucleus of protons and electrons.
  • Light illuminates objects. In a nutshell, different elements and molecules react to light in different ways because of their atomic structure and the particular way they combine to form mixtures or compounds.
  • In the case of an opaque object, it is the molecules that form its surface that determine what happens when light strikes it. Translucent and transparent objects behave differently because light can travel through them.
  • Another factor that needs to be taken into account when light strikes an object is surface finish. A smooth and polished surface behaves differently from one that is rough, textured or covered in ripples.

Object

An object is a material thing that can be seen and touched.

  • An object is intuitively assumed to exist and to be responsible for a unified experience, consisting of visual and other sensations and perceptions.
  • Every object, material, medium or substance that we can see is made of matter of one kind or another. The key differentiating factor is the elements and molecules they are constructed from.
  • You will have come across the elements that make up the periodic table.
  • A close look at molecules reveals that they are made up of atoms composed of electrons surrounding a nucleus of protons and electrons.
  • Light illuminates objects. In a nutshell, different elements and molecules react to light in different ways because of their atomic structure and the particular way they combine to form mixtures or compounds.
  • In the case of an opaque object, it is the molecules that form its surface that determine what happens when light strikes it. Translucent and transparent objects behave differently because light can travel through them.
  • Another factor that needs to be taken into account when light strikes an object is surface finish. A smooth and polished surface behaves differently from one that is rough, textured or covered in ripples.

Observation of colour

About the observation of colour
  • The human eye is sensitive to the visible spectrum, which includes all the spectral colours ranging from approximately 400 to 700 nanometers.
  • The sensitivity of the eye to the visible spectrum enables us to perceive colours when light interacts with objects.
  • The visual perception of colour by an observer is associated with words such as red, blue, yellow, etc., which are commonly used to describe hue or dominant wavelength.
  • The colour an observer sees depends on:
    • The wavelengths of visible light present in the environment.
    • The wavelengths absorbed, transmitted, or reflected by an object or medium.
  • The perception of colour can be affected by factors such as brightness, contrast, and saturation, which are related to the amount of light present in a stimulus and its interaction with the eye and brain.
  • The observed colour of light is determined by its wavelength, not its frequency. However, as light travels from one medium to another, such as from air to glass, the colour seen by an observer may change due to refraction causing colours to disperse in different directions.

Observer

A human observer is a person who engages in observation by watching things.

Observer

A human observer is a person who engages in observation or watches something.

  • Humans observe themselves, each other and the world around them.
  • The act of observation allows us to develop our understanding of ourselves and interact with the world.
  • When an observer sees something they are engaging in visual perception.
  • An observer can take many forms:
    • A person watching an ocean sunset or the sky at night.
    • A person studying a baby’s face.
    •  A person studying something they can’t see by collecting data from an instrument or machine.
    • A person conducting an experiment in a laboratory setting.
  • In everyday life, an observer feels involved in the things they observe.
  • Observers can have biases and subjective interpretations, which may affect their observations.
  • A scientific observer is someone who avoids making unnecessary changes to the object of their observations.
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References

A human observer is a person who engages in observation by watching things.

Observer effect

The observer effect is a principle of physics and states that any interaction between a particle and a measuring device will inevitably change the state of the particle. This is because the act of measurement itself imposes a disturbance on the particle’s wave function, which is the mathematical description of its state.

  • The concept of observation refers to the act of engaging with an electron or other particle, achieved through measuring its position or momentum.
  • In the context of quantum mechanics, observation isn’t a passive undertaking, observation actively alters a particle’s state.
  • This means that any kind of interaction with an atom, or with one of its constituent particles, that provides insight into its state results in a change to that state. The act of observation is always intrusive and will always change the state of the object being observed.
  • It can be challenging to reconcile this with our daily experience, where we believe we can observe things without inducing any change in them.
  • The observer effect implies that:
    • Measuring a particle’s position compels it to assume a specific location.
    • Measuring a particle’s momentum compels it to adopt a particular measurable value.
  • The observer effect applies to all quantum systems, including atoms, molecules, and photons.
  • The observer effect is not fully understood. There are many different theories about how it works, but no one theory is universally accepted.
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References

Summary

Observer’s point of view

To understand rainbows it is important to sort out what an observer is actually looking at.

  • Rainbows only exist in the eyes of an observer.
  • Every observer sees a different rainbow produces by a unique set of raindrops that happen to be in the right place at the right time.
  • The individual raindrops that result in the appearance of a rainbow for one observer are always different from the raindrops that produce a rainbow for someone else.
  • As an observer moves, their rainbow moves with them. Seen from a car window, the rainbow appears stationary whilst the landscape rushes past.
From an observer’s point of view
  • Atmospheric rainbows appear to an observer as arcs of colour across the sky. From an aeroplane, a rainbow can appear as entire circles of colour.
  • Even from the ground, it is easy to deduce that every rainbow has a centre point around which the arcs of a rainbow are arranged.
  • The exact position in the sky where an atmospheric rainbow will appear can be anticipated by working out where its centre will be.
  • The centre of a rainbow is always on an imaginary straight line that starts at the centre of the Sun behind you, passes through the back of your head, out through your eyes and extends in a straight line into the distance.
  • The eyes of an observer are always aligned with the rainbow axis.
  • To an observer, the rainbow axis appears as a point, not a line, and that imaginary point marks the centre of where every rainbow will appear.
  • The idea that a rainbow has a centre corresponds with what an observer sees in real-life.
  • The idea of a rainbow axis or anti-solar point corresponds with a diagrammatic view showing the scene in side elevation.
Looking for rainbows
  • To work out where a rainbow might appear:
    • Turn your back on the Sun.
    • If you can see your shadow, look at the head. The axis of the rainbow runs from the Sun behind you, through your eyes and through the head of your shadow. Imagine where your eyes might be in your shadow. If a rainbow appears that point will be its centre.
    • If you can’t see your shadow, just try and imagine the line from the Sun, passing through your head and then extend it away from you till it reaches the landscape. At whatever point it touches, that will be the centre.
    • Unless you are in a plane, the centre point is always below the horizon so on the ground or in the landscape in front of you.
    • Now, with the Sun behind you spread out your arms to either side or up and down at 450 from the centre point.
    • Swing them round like the blades of a windmill. That is where your primary rainbow will appear.
Remember that:
  • Every observer has a rainbow axis and a centre-point on that axis that moves with them as they change position. It means that their rainbow moves too.
  • The centre of a secondary rainbow is always on the same axis as the primary bow and shares the same anti-solar point.
  • To see a secondary rainbow look for the primary bow first – it has red on the outside. The secondary bow will be a bit larger with violet on the outside and red on the inside.
Rainbows as discs of colour
  • Close consideration of why rainbows appear as arcs or circles can be explained by the idea that an observer is looking at superimposed, concentric discs of colour.
  • Think in terms of each observed band of colour within a rainbow forming on the edge of a separate coloured disc.
  • The area close to the circumference of each disc produces the most intense and brilliant colour.
  • The intensity of each colour drops sharply away from the circumference of its disc and towards the centre.
  • The observed colour of each disc corresponds with the band of wavelengths that produces it.
  • The fact that we see distinct bands of colour in a rainbow is often described as an artefact of human vision.
  • Each disc contributes small amounts of its own colour to the area towards the shared centre of the six concentric discs making the sky appear lighter.

Opacity

Opacity refers to the extent to which an object or surface hinders or blocks light from passing through and so obstructs light from reaching objects or space beyond.

  • Opacity can be caused by various factors, such as absorption, reflection, and scattering.
  • An entirely opaque substance reflects and absorbs all incident light, with no transmission or scattering.
  • When light strikes an interface between two media, some light is reflected, some is absorbed, and some is scattered:
    • The remaining light undergoes refraction and is transmitted through the second medium.
    • Opacity therefore measures the ability of the second medium to obstruct light.
  • An opaque object is neither transparent (allowing all light to pass through) nor translucent (allowing some light to pass through).
  • Opacity of some media varies with the wavelengths of light. For example, certain types of glass are transparent in the visual range but mostly opaque to ultraviolet light.
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References

Optic chiasm

Optic chiasm

The optic chiasm is the part of the brain where the optic nerves partially cross. It is located at the bottom of the brain immediately below the hypothalamus.

The cross-over of optic nerve fibres at the optic chiasm allows the visual cortex to receive the same hemispheric visual field from both eyes. Superimposing and processing these monocular visual signals allows the visual cortex to generate binocular and stereoscopic vision.

So, the right visual cortex receives the temporal visual field of the left eye, and the nasal visual field of the right eye, which results in the right visual cortex producing a binocular image of the left hemispheric visual field. The net result of optic nerves crossing over at the optic chiasm is for the right cerebral hemisphere to sense and process left-hemispheric vision, and for the left cerebral hemisphere to sense and process right-hemispheric vision.

 

Optic chiasm

The optic chiasm is the part of the human brain where the optic nerves partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.

  • The cross-over of optic nerve fibres at the optic chiasm allows the visual cortex to receive the same hemispheric visual field from both eyes.
  • Superimposing and processing these monocular visual signals allow the visual cortex to generate binocular and stereoscopic vision.
  • For example, the right visual cortex receives the temporal visual field of the left eye, and the nasal visual field of the right eye, which results in the right visual cortex producing a binocular image of the left hemispheric visual field. The net result of optic nerves crossing over at the optic chiasm is for the right cerebral hemisphere to sense and process left hemispheric vision, and for the left cerebral hemisphere to sense and process right hemispheric vision.
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Optic nerve

Optic nerve

The optic nerve is the cable–like grouping of nerve fibres formed from the axons of ganglion cells that transmit visual information towards the lateral geniculate nucleus.

The optic nerve contains around a million fibres and transports the continuous stream of data that arrives from rods, cones and interneurons (bipolar, amacrine cells). The optic nerve is a parallel communication cable that enables every fibre to represent distinct information about the presence of light in each region of the visual field.

Optic nerve

The optic nerve of the human eye is the cable–like grouping of nerve fibres formed from the axons of ganglion cells that transmit visual information towards the lateral geniculate nucleus.

  • The optic nerve contains around a million fibres that transport continuous stream of data which have been received from rods, cones and the intermediate neuron types, bipolar and amacrine cells.
  • The optic nerve is a parallel communication cable that enables every fibre to represent distinct information about the presence of light in each region of the visual field.
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optic radiation

The optic radiation are tracts formed from the axons of neurons located in the lateral geniculate nucleus and lead to areas within the primary visual cortex.

  • There is an optic radiation on each side of the brain. Each one carries visual information through two divisions called the upper and lower divisions to their corresponding cerebral hemisphere.
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optical density

Optical density is a measure of how much a material resists and slows the transmission of light.

  • The optical density of a material is not directly related to its physical density.
  • The higher the optical density of a material, the slower light travels through it.
  • The lower the optical density of a material, the faster light travels through it.
  • A vacuum is not a medium and has zero optical density.
  • Light travels through a vacuum at the maximum possible speed of light which is 299,792 kilometres per second.
  • Optical density and refractive index are related properties.
    • In general, materials with higher optical density tend to have higher refractive indices and vice versa.
    • The greater the difference in refractive index between two materials, the more they will bend light when they come into contact.
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optical density

Optical density is a measurement of the degree to which a refractive medium slows the transmission of light.

  • The optical density of a medium is not the same as its physical density.
  • The more optically dense a medium, the slower light travels through it.
  • The less optically dense (or rare) a material is, the faster light travels through it.
  • A vacuum has the least optical density and so light travels through it at a maximum speed of 299,792 kilometres per second.
  • Optical density accounts for the variation in refractive indices of different media.

https://en.wikipedia.org/wiki/Absorbance

Optical phenomena

Optical phenomena result from the interactions between light and matter. Optical phenomena include absorption, dispersion, diffraction, polarization, reflection, refraction, scattering and transmission.

  • Optics is the branch of physics that studies the behaviour and properties of light, including visible, ultraviolet, and infrared light.
  • Visible, ultraviolet, and infrared light, along with X-rays, microwaves, and radio waves, are all examples of electromagnetic radiation.
  • Many optical phenomena can be explained using the classical electromagnetic theory that describes light in terms of waves.
  • Geometric optics describes light as travelling in straight lines and changing direction when passing through or reflecting from surfaces. These phenomena can be analysed using ray diagrams.
  • Ray diagrams are useful when explaining the workings of everyday objects such as mirrors, lenses, telescopes, microscopes, lasers, and fibre optic devices.
  • Some optical effects such as diffraction and interference can be explained in terms of the particle-like properties of photons and with reference to the field of quantum mechanics.
  • About photons:
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Summary

Optics

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

  • Most optical phenomena can be accounted for using the classical electromagnetic description of light (wavelength, frequency and intensity) but they can also be modelled as particles called photons.
  • Optics is both a field of physics and an area of engineering. It has been used to create many useful devices, including eyeglasses, cameras, telescopes, and microscopes. Many of these devices are based on lenses, which can focus light and produce images of objects that are larger or smaller than the original.
  • New discoveries are being made in the field of optics For example, The first working fibre-optic data transmission system was demonstrated in 1965. Less than 60 years later, fibre optics are now used to send vast amounts of data through thin optical fibre around the world.
  • Contemporary specializations within the field of optics include:
    • Geometrical optics is a branch of optics that deals with the behaviour of light as a collection of rays that propagate in straight lines and are subject to reflection and refraction.
    • Physical optics is a branch of optics that describes the behaviour of light as both a wave and a particle and includes wave phenomena such as diffraction and interference that are not explained by geometrical optics.
    • Quantum mechanics is a branch of physics that describes the behaviour of light as both a wave and a particle and investigates the interactions between light and matter.
About geometrical optics
  • Geometrical optics, also known as ray optics, is one of the two main branches of optics, the other being physical optics.
  • Geometrical optics is based on the assumption that light travels as a straight line and is useful in explaining various optical phenomena, including reflection and refraction, in simple terms.
  • Geometrical optics is a useful tool in analyzing the behaviour of optical systems, including the image-forming process and the appearance of aberrations in systems containing lenses and prisms.
  • The underlying assumptions of geometrical optics include that light rays:
    • Propagate in straight-line paths when they travel in a uniform medium.
    • Bend, and in particular, refract, at the interface between two dissimilar media.
    • Follow curved paths due to the varying refractive index of the medium.
    • May be absorbed as photons and transferred to the atoms or molecules of the absorbing material, causing the absorbing material to heat up or emit radiation of its own.
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References

Orders of rainbows

Primary rainbows are sometimes referred to as first-order bows. First-order rainbows are produced when light is reflected once as it passes through the interior of each raindrop.

Secondary rainbows are second-order bows. Second-order bows are produced when light is reflected twice as it passes through the interior of each raindrop.

  • Each subsequent order of rainbows involves an additional reflection inside raindrops.
  • Higher-order bows get progressively fainter because photons escape droplets after the final reflection. As a result, insufficient light reaches an observer to trigger a visual response.
  • Each higher-order of bow gets progressively broader spreading photons more widely and reducing their brightness further.
  • Only first and second-order bows are generally visible to an observer but multi-exposure photography can be used to capture them.
  • Different orders of rainbows don’t appear in a simple sequence in the sky.
  • First, second, fifth and sixth-order bows all share the same anti-solar point.
  • Zero, third and fourth-order bows are all centred on the Sun and appear as circles of colour around it.

https://www.atoptics.co.uk/rainbows/orders.htm

Oscillation

An oscillation is a periodic motion that repeats itself in a regular cycle.

  • Oscillation is a characteristic of waves, including electromagnetic waves.
  • Examples of oscillation include the side-to-side swing of a pendulum and the up-and-down motion of a spring with a weight attached.
  • Electromagnetic waves oscillate due to the transmission of energy by their electric and magnetic fields.
  • An oscillating movement is typically around a point of equilibrium if the motion repeats itself around an equilibrium position.
  • Oscillations can occur in a wide range of physical systems, such as mechanical systems, electrical circuits, and chemical reactions.
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References

An oscillation is a periodic motion that repeats itself in a regular cycle. An oscillating movement is always around an equilibrium point or mean value. It is also known as a periodic motion.

  • The term oscillation denotes something that moves in one direction, then moving back in a repeating pattern.
  • An electromagnetic wave describes an oscillatory motion as the electric field and then the magnetic field take turns to increase to their maximum values and then drop back to zero.