The speed of light in air is very close to 300 000 000 m/s. which is nearly a million times faster than the speed of sound, which is 340 m/s. 300 000 000 m/s is often written as 3 x \(10^8\) m/s.

If a light ray hits the mirror with an angle of incidence of 45°, it will be reflected with an angle of reflection of 45°.

When white light passes through a prism it can be split up into its colours. The band of colours seen is called the spectrum of white light.

The greater the change of speed of light at a boundary, the greater the refraction. Light is bent more by glass than by water because glass is denser than water and so slows it down more.

Shadows are also formed because light travels in straight lines. When an object that will not allow light to pass through it (an opaque object) is placed in front of a light, a shadow is cast on the ground or a screen behind it. The object stops the light reaching the ground and the shadow is the shape of the object.

The total shadow or umbra is the shadow's dark core. The partial shadow or penumbra is the lighter outer part of the shadow.

This is called ‘reflected metering’. While it’s a good, reliable way to get a quick reading of a scene, it is easily compromised by variances in tone and colour in different subjects. Subjects that are lighter than neutral grey – white snow, wedding dresses, etc – will appear brighter than they are, causing the camera to underexpose. Meanwhile, subjects darker than neutral grey, like a black cloth or a black cat, will reflect less light and cause the camera to overexpose.

A pinhole camera consists of a box or tube with a translucent screen at one end and a tiny hole (the pinhole) made in the other end. Light enters the box through the pinhole and an image is formed on the translucent screen. The image is upside down and smaller than the object.

In a ray diagram, the mirror is often drawn as a straight line with thick hatchings. The side with the hatchings indicates the non-reflective side.

This makes it much more difficult to get well-exposed results out of a camera that is otherwise perfectly functional. Getting a hotshoe-mounted or handheld light meter can be a more cost-effective way to keep the camera running than taking it down to the repair shop. Light meters are also handy if you’re interesting in conducting photographic experiments such as building your own pinhole camera.

An eclipse of the Sun, or Solar Eclipse, occurs when a new Moon passes directly between the Sun and the Earth, blocking out the Sun's rays and casting a shadow on regions of the Earth. As a result, daylight briefly turns to darkness.

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The angle of refraction is less than the angle of incidence. Therefore, when light travels from air into glass it bends towards the normal.

For one, it frees you to move around your scene or set and measure light in different areas. It allows you to conduct what’s called “incident metering” – meaning when you measure the amount of light falling onto your subject, rather than the amount of light bouncing off it, which is what your camera’s system is measuring when you point it at something.

Remember: Angles of incidence and refraction are always measured between the normal and the ray of light. Make sure that the normal goes through the zero of the protractor.

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A pinhole camera is another good example of the fact that light travels in straight lines. They can be useful to look at the image of a dazzling object such as the Sun which you should never look at directly. Forming an image on the screen makes watching an eclipse safe.

Notice that the ‘real’ rays, the ones leaving the object and the mirror, are shown as solid lines. The ‘virtual’ rays, the ones that appear to come from the image behind the mirror, are shown as dashed lines. Remember that each incident ray will obey the law of reflection.

A light meter is as it sounds – a device for measuring the available light in a scene so that you can set your camera’s exposure accordingly. Yes, all modern cameras have their own built-in metering systems. However, a light meter offers a number of advantages that makes it a useful tool for those who require precise exposure accuracy.

One way to remember the order: ‘Richard Of York Gave Battle In Vain’.These are the same colours seen in a rainbow. A rainbow is formed when sunlight shines through water. The tiny water droplets act as prisms, refracting each colour of the white light by a different amount, to produce the spectrum of light arched across the sky.

One particular use for a hotshoe-mounted camera light meter is if you shoot film. Many analogue photographers use second-hand vintage SLRs or large-format cameras, and often on these old cameras, the first thing to fail is the built-in light meter (if it even has one in the first place).

A non-luminous object does not give out its own light. We see it because it reflects the light from a luminous object, like the Sun or a candle, towards our eyes.

That means in one second light travels a distance of 300 000 000 m – which is about seven and half times around the world, in one second. Which is pretty fast! Not even Superman managed that. In fact, nothing can travel faster than the speed of light.

A total solar eclipse happens when the Moon casts the darkest part of its shadow, called the umbra, on Earth. The Moon appears to cover the entire disk of the Sun. However, you only see a total solar eclipse if you are in a region covered by the Moon's full shadow, its umbra. Those outside the path in the partial shadow, or penumbra, see a partial eclipse.

The diagram shows refraction of light passing into, and then out of, a glass block. The same would happen for a Perspex block or for water.

Light is a type of electromagnetic radiation that can be detected by the eye. It travels as a transverse wave. Unlike a sound waves, light waves do not need a medium to pass through, they can travel through a vacuum.

A virtual image is an image from which rays of light appear to diverge, and do not actually pass through. A virtual image cannot be formed on a screen.

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In the third example, if a light ray travelling along the normal hits a mirror, it is reflected straight back along the normal, the way it came.

A mirror reflects light. It is made by putting a thin reflecting layer behind a piece of glass. The reflecting layer is often silver nitrate, held in place by a coat of paint. Most every day mirrors are flat and are called plane mirrors.

The angle of emergence is greater than the angle of refraction. Therefore, when light travels from glass into air it bends away from the normal.

If a surface is rough, diffuse reflection happens. Instead of forming an image, the reflected light is scattered in all directions.

Light meters can be an invaluable tool for photographers and videographers alike. Whether you shoot in the studio or on location, having a reliable light meter at your disposal is a time-honoured way of making sure you get accurate exposures, time and again.

The next total solar eclipse to occur in the UK will be on 23 September 2090. It will be visible in Cornwall and much of the south coast of England and last 3 minutes and 36 seconds just minutes before sunset. Partial eclipse can be seen from parts of the UK on 10th June 2021, 25th October 2022, 8th April 2024 and the 29th March 2025.

Light meters come in two main varieties – handheld and hotshoe-mounted. In general, handheld meters are the premium option, with cutting-edge technology and extra functions like flash measurement, touchscreens and wireless triggering of compatible flash remotes. Most meters are battery powered, but there are also battery-free analogue meters available, which can be tremendously handy if you don’t fancy the idea of yet another device you need to remember to charge. Hotshoe-mounted meters tend to be simpler and more affordable.

This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles and so the reflected rays are not parallel.

When measuring the angle of incidence, i, or angle of reflection, r, it is important to place the zero line of the protractor along the normal. This will ensure that you measure the angle between the normal and the ray and not the angle between the mirror and the ray.

Compare the size of the angle of refraction, r, with the angle of incidence, i.Compare the size of the angle of emergence, e, with the angle of refraction, r.

300 000 000 m/s (or 300 million m/s) is approximately the same as 670 000 000 miles per hour (or 670 million miles per hour).

In genres like professional portrait or product photography, it is critically important to get accurate, balanced exposures. With a light meter you can ensure that your studio lights are at just the right level relative to each other, that your flash is firing at the correct intensity, and more. A light meter can be your best friend in making sure you get it all right every time.

Likewise, if light is incident along the normal when it passes from glass into air it still speeds up but its direction does not change – it passes straight through.

If light is incident along the normal when it passes from air into glass it still slows down but its direction does not change – it passes straight through.

The spectrum is produced because different colours of light travel at different speeds in glass.This means that each colour of light is refracted by a different amount when it enters the glass and when it leaves.

Here are the seven colours of the spectrum listed in order of their frequency, from the lowest frequency to the highest frequency: