# Y8 Light Revision

• Light Y8 Revision
• Travelling light
• Shadows are actually patches where light has been blocked by an object.
• Light travels in straight lines and is a lot faster than sound.
• It does not need anything to move through and cannot move through anything opaque.
• Translucent things do let light through but they scramble it so you don't see through clearly.
• Light is 'transmitted' when it goes through something transparent, is absorbed or reflected when going onto  something opaque and is absorbed best by black surfaces.
• Reflection
• You see an image in a mirror as the rays of light seem to come from the thing inside the mirror. In a plane mirror the object is the same size and distance from the mirror
• Specular reflection is where light hits a smooth surface (like a mirror or polished metal) and is bounced back evenly so we see a clear image.
• The law of reflection is that the angle of incidence (the angle the light came in at) is the same as the angle of reflection (the angle the light left the surface at). The normal is a metaphorical line drawn at 90 degrees to the surface the light bounced off at.
• Diffuse reflection is where light hits a rough surface and comes off at a lot of different angles meaning you do not see an image.
• Refraction
• When lights hits a new medium, the speed and direction changes
• Happens at the interface between two things
• When light enters a new medium it bends towards the normal. When it comes out it bends away
• Convex lens bends light inwards toward its focal point
• Concave lens bend lights away
• Colour
• White light is a mixture of red blue and green
• The visible spectrum is from purple to red and outside of it are : UV light and infared
• When white light hits a prism is splits into a spectrum of 7 colours (what we know as the rainbow)
• We see objects as coloured because they only reflect some of the spectrum
• Filters only transmit one colour and block the rest
• Red is lowest frequency in transverse waves and that frequency rises until violet (highest)
• Cameras and Eyes
• A camera consists of a lens, a sensor, a shutter and an aperture
• An eye consists of rod cells, cone cells, optic nerve, iris, a lens, a pupil and a cornea
• A lens focuses light
• A sensor converts light to electric signals. The optic nerve does the same in an eye and carried the impulses to the brain
• The aperture lets light into the camera. In an eye, the pupil does this job
• The shutter opens to let light in. In the eye, the iris lets light in
• The rod cells detect faint light and the cone cells detect primary colours
• The cornea is transparent to help focus light coming into the eye