LIGHT

Question 1

How fast can light travel

Answer 1

Light travels 300,000 km per second in space taking almost 10 minutes to reach earth. Light consists of particles called photons that travel as a wave.

Question 2

What are the sources of light

Answer 2

The sources of light can be luminous objects and substances that emit light on their own. A type of source is incandescent which is an object or substance that emits light because they are hot. eg) lightbulbs, flames,sun.
Non-incandescent is a substance or object that emits light without getting hot. eg) LED lights, some deep sea fish, glow-worms.
Living things that emit light without heat are referred to as bioluminescent.

Question 3

How can we see objects?

Answer 3

most things that you see are non-luminous( they do not emit their own light) however we are able to see these objects because light from luminous objects is reflected from them. Eg) the moon is not a luminous object, its surface simply reflects light from the sun.

Question 4

Seeing light

Answer 4

light can be seen when looking at a luminous object or when looking at an object that reflects light into your eyes. Light is not normally visible between its source and any surface that it strikes. You can only see a beam of light if there are particles in the air to scatter light back to your eye.

Question 5

When light meets a substance it can be…

Answer 5

Reflected- when light bounces of the object.
Absorbed- when light is taken into the object.
Transmitted- when light passes through the object.

Question 6

Types of objects

Answer 6

Transparent- Materials like glass that allows light to pass through.
Opaque- Objects that absorb or reflect all light striking through.
Translucent- only allows some light to pass through the object, unable to see through clearly.

Question 7

The electromagnetic spectrum

Answer 7

Visible light is just one part of a ‘family’ of forms of energy known as electromagnetic radiation emitted by the Sun and other stars.
Along with visible light the electromagnetic spectrum consists of radio waves microwaves, infra-red radiation ultraviolet radiation x-rays and gamma rays. All types of electromagnetic radiation can be produced artificially here on Earth.

Question 8

Visible light spectrum

Answer 8

In 1666, the English scientist Isaac Newton passed a narrow beam of light through a glass triangular prism. Newton classified the colours of the spectrum as red, orange, yellow, green, blue, indigo & violet.
The splitting of white light into the colours that make up white light is called dispersion.

Question 9

Dispersion of white light

Answer 9

Each colour from the original beam of light has its own particular wavelength & each wavelength is slowed differently by the glass.
The amount of refraction increases as the wavelength of light decreases.
Shorter wavelengths of light (violet & blue) are slowed more and consequently experience more bending than longer wavelengths (orange & red).

Question 10

Light waves

Answer 10

Light travel via waves known as transverse waves. This is when the waves of energy move up and down and travel through space. Radio waves have larger wavelengths and can pass through a brick wall and that is why you can tune into a radio inside your home.

Question 11

Rainbows

Answer 11

rainbows are formed because rain droplets act as prisms. The droplets disperse white light into the seven colours of the spectrum.
The sun behind you shines on the rain droplets causing the rainbow.

Question 12

Rays

Answer 12

Light is especially important to us because of its ability to form images.
The reflection of light allows you to see images in mirrors. When you take a photo, the image is created when light is bent by a lens. Light travels in straight lines.
The lines that are used to show the path of light are called rays. A beam of light is a stream of light rays.

Question 13

Reflection

Answer 13

When you look in a mirror you see an image of yourself.
If the mirror is a plane or flat mirror, the image will be very much like the real you.
If the mirror is curved, the image might be quite strange.
Reflection depends on how smooth a surface is

Question 14

Law or reflection

Answer 14

Whenever light is reflected (angle of reflection)from a smooth, flat surface, it bounces away from the surface at the same angle from which it came (angle of incidence).

Question 15

Law of reflection rule

Answer 15

Angle of Incidence = Angle of Reflection

Question 16

Reflection of light from a mirror

Answer 16

The normal: a dotted, imaginary line drawn at 90° (perpendicular) to the mirror.
Incident ray: incoming light.
Reflected ray: light leaving the mirror.
Angle of incidence: angle between the incident ray and the normal.
Angle of reflection: angle between the reflected ray and normal.

Question 17

Plane mirrors

Answer 17

When we look in a plane (flat) mirror:

1. The image is not real-it is a virtual image (it cannot be captured on paper or a screen).  
2. The image is the same distance behind the mirror as the real person in front of the mirror.
3. The image is the same size as the original, but it is laterally inverted (reversed sideways).

Question 18

Mirror images

Answer 18

When looking at a mirror we know that the object is NOT behind the mirror. This is termed virtual image

Question 19

Spherical mirrors

Answer 19

Spherical mirrors are mirrors having curved surfaces that are painted on one of the sides.

Spherical mirrors in which inward surfaces are painted are known as convex mirrors.

Spherical mirrors in which outward surfaces are painted are considered concave mirrors.

Question 20

Convex mirrors

Answer 20

The convex mirror allows the observer to see a larger field of view.
They are used to see traffic around a corner, for car mirrors and in shops to see people in the aisles

Question 21

Concave mirrors

Answer 21

The concave mirrors allows the observer to see close up .They can also concentrate light for uses such as a light house, telescope or heating water.

Question 22

What is refraction

Answer 22

Refraction is the bending of light as it passes, at an angle, from one transparent material into another.
The light bends because it changes speed.
Light travels at different speeds through different substances.
The differences in its speed result in different amounts of bending, or refraction, as light passes from one substance into another.
The more dense the material the more the light bends towards the middle of the object.

Question 23

What are the functions of each structure of the eye?

Answer 23

Pupil- allows light into the eye.
Iris- Controls the size of the pupil.
Lens- Focuses light onto the retina
Retina- Detects light using cells called photoreceptors
Optic nerve- Receives signals from the retina and sends them to the brain.
Sclera- Protects the eye and helps maintain its shape.
Choroid- Contains blood vessels, which brings nutrients to the eye.
Cornea- Protects the front of the eye.
Vitreous humor- Helps the eye maintain its shape
Aqueous humor- Brings nutrients to the cornea and lens, which lack blood vessels.

Question 24

What are the types of photoreceptors?

Answer 24

Photoreceptors are located on the back of the eye. The two types are rods and cones. Rods respond slowly and operate in dim light, and cannot recognise colour. There are more rods in the eye than cones. Cones are responsible for colour vision and can recognise red blue and green light.

Question 25

What are the problems with the eyes?

Answer 25

Myopia, Hyperopia and presbyopia

Question 26

What is Myopia

Answer 26

Can focus on near objects, but not distant objects.
The eyeball is too long and the lens focuses the image in front of the retina.
The light rays need to be spread out (diverged) to refocus image on retina.
Glasses with concave lenses are used.

Question 27

What is Hyperopia

Answer 27

Can see distant objects, but close objects are blurry.
The eyeball is too short and the lens is focusing the image behind the retina.
The light rays need to be drawn in closer together (converged) to refocus image on retina.
Glasses with convex lenses are used.

Question 28

What is Presbyopia

Answer 28

Presbyopia, is an age-related eye condition that is found in older people. This condition causes the lens in the eye to harden, so that light is focused behind the retina, rather than in front.

Question 29

Convex lenses

Answer 29

Convex lenses are thicker at the centre than at the edges.
They cause light rays to converge (or come together).
The focus or focal point is the point where the rays cross or meet.
The focal length is the distance from the focus to the middle of the lens.

Question 30

Concave lenses

Answer 30

Concave lenses are thinner in the centre than at the edges.
Concave lenses cause light rays to diverge.
The focus or focal point is on the other side of the lens.