A Brief Look at LIGHT

Light is a form of electromagnetic radiation that is detectable by the eye… but we can’t see it!!!

The Speed of Light in air is about 300 000 000 m/s. It’s fast! depends on the material the light is travelling through. is the fastest possible speed for any object???

Diagrams with Light are referred to as ray diagrams where a ray is a single path followed by light and a beam is a ‘bundle’ of light rays.

When light strikes matter It can be affected in 3 different ways: Transmitted: light passes through a medium Ex. Windows Reflected: light bounces off an object Ex. Mirrors Absorbed: light disappears (or certain wavelengths) Green object  all wavelengths of light except green are absorbed

Classifying Objects Objects may be classified based on how well they transmit light: Transparent: transmits ALL light Opaque : transmits NO light Translucent: transmits SOME light

Electromagnetic Spectrum Light travels as an Electromagnetic wave which is made up of particles of energy called photons. Electromagnetic waves are made up of electrical energy and magnetic energy Wavelength: the distance between peaks on a wave

Electromagnetic Spectrum There are many types of electromagnetic waves. The main difference between them is their wavelength Electromagnetic Spectrum represents different types of waves arranged according to their wavelength

Electromagnetic Spectrum p.409 text

Electromagnetic Spectrum Uses

Break: Watch Eureka video http://www.animatedscience.co.uk/flv/

The Reflection of Light Regular Reflection: this is reflection of light from smooth shiny surfaces. The next slide diagram shows how light behaves during regular reflection.

Laws of Reflection Normal Incident Ray Angle of Incidence Angle of Reflection Reflected Ray 90o Mirror Point of incidence/ axis

Laws of Reflection First Law: The angle of incidence is equal to the angle of reflection Normal Incident Ray Angle of Incidence Angle of Reflection Reflected Ray Mirror

Laws of Reflection Laws of Reflection Second Law: The incident ray, reflected ray, and normal all lie on the same plane Normal Incident Ray Angle of Incidence Angle of Reflection Reflected Ray Mirror

Diffuse Reflection Many surfaces appear to be smooth, however when they are viewed under a microscope it is clear they are not. Because of the uneven surface, the light rays are scattered in many directions (diffused).

Diffuse Reflection Further examination of a irregular surface show that they too obey the laws of reflection (ie. Angle of incidence = angle of reflection).

Diffuse Reflection Most objects are made of rough surfaces (and therefore scatter light); if this did not happen, indoor lighting would not be effective. ie. Walls, floors, ceilings, etc. scatter light in all directions, making them visible.

Optical Images An image is the representation of an object formed by the interaction of light rays.

Optical Images An image is the representation of an object formed by the interaction of light rays. Characteristics: Size: same size, bigger or smaller than object Attitude: image is upright, flipped or laterally inverted Location: behind the mirror or in front of the miror the same distance as the object Type : virtual or real

Images Formed in Plane Mirrors How do I see an image of the arrow??

Images Formed in Plane Mirrors Light from the arrow hits the mirror

Images Formed in Plane Mirrors ..and is reflected into my eye

Images Formed in Plane Mirrors The image!! ..and my brain ‘sees’ the image where the light appears to have come from!

Characteristics of a PLANE MIRROR Image Size: same size as object Attitude: image is upright, and laterally inverted Location: behind the mirror the same distance from the mirror as the object Type : virtual