Optics

Optics: lenses, mirrors, and

electromagnetic spectrum

Physics

Properties of Light

1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect light into

our eyes4) Shadows are formed when light is blocked by

an object

Luminous and non-luminous objects

A luminous object is one that produces light.

A non-luminous object is one that reflects light.

Visible spectrum

VisibleEach color is a different size wave.

Red the longest & violet the shortest• Emitted by– The sun and other

astronomical objects– Laser pointers– Light bulbs

• Detected by– Cameras (film or digital)– Human eyes– Plants (red light)– Telescopes

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What are sun rays?• The sun emits several kinds of electromagnetic radiation:

Visible (Vis), Infrared (IR) and Ultra Violet (UV)

Each kind is distinguished by a characteristic wavelength, frequency and energy

• Higher energy radiation can damage our skin

High Energy Low Energy

Colour• White light is not a single colour; it is made

up of a mixture of the seven colours of the rainbow.

We can demonstrate this by splitting white light with a prism:

*Animation

The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection

The same !!!

Clear vs. Diffuse Reflection

• Smooth, shiny surfaces have a clear reflection:

Rough, dull surfaces have a diffuse reflection.

Diffuse reflection is when light is scattered in different directions

Refraction• The change in direction of a wave as

is crosses the boundary between two media in which the wave travels at different speeds.

Convex lenses• Refracts parallel light rays so they come

together at a single point (convergence). • Distance from center of lens to focal point

= focal length.• The thicker the middle of the lens the

shorter the focal length.

Concave lenses

• Refracts the rays so they come apart. -Known as divergence.

• Always forms a virtual image.

• Show overhead of concave lens.