Light Waves

We see objects because they emit or reflect light Cataract is an eye problem when one of the eyes become cloudy so the people are unable to see It is possible to remove this damaged part of the eye and replace it with a clear plastic that will again allow light to enter the eye.

There are many sources of light like the Sun, the stars, fires, light bulb… Objects that emit their own light are called luminous objects When the emitted light enters our eye we see the objects Objects that don’t emit light are called non-luminous objects We see those objects because of the light they reflects

Reflection in a Plane Mirror Plane mirror Normal Incident rayReflected ray Angle of incidence Angle of reflection Light waves are transverse waves and like all waves can be reflected, refracted and diffracted

Reflection in a Plane Mirror Plane mirror Normal Incident rayReflected ray Angle of incidence Angle of reflectio n The angle of incidence is equal to the angle of reflection Laws of reflection :

angle of incidence (i) = angle of reflection (r) reflected rayincident ray i r normal plane mirror point of incidence The incident ray, the reflected ray and the normal all lie in the same plane (i.e. the two rays and the normal can all be drawn on a single sheet of flat paper).

Mirrors are used to change the direction of la ray of light

A periscope is used to see over or around objects

When you look into plane mirror you see images of the room that appear to be behind the mirror. This images are created by rays of light from objects inside the room striking the mirror and being reflected into your eyes Because rays of light normally travel in straight lines your brain interprets the rays as having come from I Images through which rays of light don’t actually pass are called virtual images. Images created with rays of light actually passing through them are called real images like on a cinema screen

Where is the image in a Plane Mirror?

The image in the mirror looks the same as the object, but it is laterally inverted (back to front).

Where is the image in a Plane Mirror? The image in the mirror looks the same as the object, but it is laterally inverted (back to front). The image formed is upright, but it is a virtual image (doesn’t really exist).

Where is the image in a Plane Mirror? The image in the mirror looks the same as the object, but it is laterally inverted (back to front). The image formed is upright, but it is a virtual image (doesn’t really exist). Dotted lines show the construction of the virtual image)

Where is the image in a Plane Mirror? Normal view from the front.

Where is the image in a Plane Mirror? Normal view from the front. Same view as seen in the rear view mirror of a car.

Where is the image in a Plane Mirror? Normal view from the front. Same view as seen in the rear view mirror of a car. The word AMBULANCE is laterally inverted so that it reads correctly when seen in a driving mirror.

Properties of an image in a plane mirror The image is far behind the mirror as the object is in front The image is the same size as the object the image is virtual it cannot be produced on a screen The image is laterally inverted that is the left side and the right side of the image appear to be interchanged

Refraction Refraction is the bending of light when it travels from one medium to another. A ‘medium’ is a material such as glass, or air, or water through which light can travel

Refraction Glass block Air Light passing through a glass block at right angles to the surface will not be refracted. The rays will pass straight through.

Refraction Glass block Normal line Air

Refraction Glass block Normal line Incident light ray Air Angle of incidence

Refraction Glass block Normal line Incident light ray Air Angle of incidence Angle of refraction Refracted light ray

Refraction Glass block Normal line Incident light ray Air Angle of incidence Angle of refraction Refracted light ray When passing from a less dense medium (air) to a more dense medium (glass) light bends towards the normal.

Refraction Glass block Normal line Incident light ray Air Angle of incidence Angle of refraction Refracted light ray

Refraction Glass block Normal line Incident light ray Air Angle of incidence Angle of refraction Refracted light ray The ray emerges from the block parallel to its original direction.

Refraction Glass block Normal line Air So why is light refracted?

Refraction Glass block Normal line Air So why is light refracted? Light is made up of many tiny waves

Refraction Glass block Air So why is light refracted? Light is made up of many tiny waves When light beams pass from air into glass one side is slowed before the other. This causes the light beam to ‘bend’

Connecting the learning. What happens as a ray of light enters a glass block? It bends towards the normal. Why? Because the speed of light changes

Real and Apparent Depth

What is the ‘refractive index’?

The refractive index of a medium (glass, water) is defined as the speed of light in a vacuum divided by the speed of light in the medium.

What is the ‘refractive index’? The refractive index of a medium (glass, water) is defined as the speed of light in a vacuum divided by the speed of light in the medium. Refractive index = Speed of light in a vacuum Speed of light in medium Medium Refractive index Vacuum Air Water Glass Diamond Perspex1.4900