Optics Notes

Grade 10 Optics

Light:

Form of energy which has properties of particles (photons) and waves.

Electromagnetic:

Describes light because light is made of oscillating electric and magnetic fields.

Wave:

Disturbance transferring energy from one point to another without transferring matter.

Crest:

Highest point on the wave.

Rest Position:

Level of water when there are no waves.

Amplitude:

The height of the wave from the rest position to the crest or the depth from the rest position to the trough.

Frequency:

Rate of Repetition of a wave (f - symbol, Hz; cycles per second - units)

When is more energy carried?

Larger the amplitude, the more energy carried and the higher frequency, the more energy the wave passes along.

Electromagnetic Spectrum:

Range of all types of radiation that has electric and magnetic fields and travels in waves.

Additive Colour Theory of Light:

White light is composed of different colours (wavelengths) of light, White light is made of green, blue and red, a secondary colour is made by mixing TWO primary colours together.

Subtractive Colour Theory of Light:

When light strikes an object, some wavelengths of light reflect off the objecy while others are absorbed, colour visible to us is the reflected wavelengths, black and blue absorbs while white reflects (blue reflects itself only).

Primary Subtractive Colours:

Magenta, yellow, cyan

Secondary Subtractive Colours:

Red, green, blue.

How is light represented and what does it show?

Lines called rays which show the direction that light travels.

What are Ray diagrams used for?

Show the path that light takes after it leaves its source.

What does each ray end with?

Ends with an arrow to indicate the direction of travel.

Materials are classified according to?

How they transmit, absorb or reflect light.

How do transparent materials act?

They transmit light freely and absorb and reflect very little light.

How do translusent materials act?

They transmit some light but not enough to see through the material clearly.

How do opaque objects act?

Opaque objects absorb and reflect light but do not transmit it.

Transmit:

Go through an object

Reflect:

Bounce off of an object

Absorb:

Soak up the light

What can ray diagrams explain?

The size and location of shadows and why some shadows are sharp while others have less distinct edges.

What does the size of the shadow depend on?

The size of the object blocking the light and its distance from the light source. Ex: The closer the object to the light source, the larger the shadow is.

Small light source =

sharp, well defined shadow

Large light source =

Fuzzy shadow because the object only partially blocks the light).

Umbra:

Part of the shadow where all light rays are blocked.

Penumbra:

The partially shaded outer region of the shadow that results from the light being partially blocked by an object.

Where do light rays come from?

Light sources that travel parallel to each other.

Regular Reflection:

The light rays strike a smooth surface, they reflect in the same direction (stay parallel).

Diffuse Reflection:

When light rays reflect off of an object with an uneven surface, they do not remain parallel, but are scattered in different directions.

Refraction:

The bending of light

Angles of light rays are always measured from a:

Normal line

The Laws of Reflections for Flat Surfaces:

The angle of incidence = the angle of reflection

Both the incident and reflected rays are in the same plane.

Plane mirror:

Any mirror that has a flat reflective surface.

When you look into a plane mirror, your image appears:

To be as far behind the mirror as you are in front of it.

Virtual Image:

Any image formed by rays that do not actually pass through the location of the image. Can not be projected on a screen.

Virtual rays are drawn as:

Dotted lines

Two types of curved mirrors:

Concave mirrors and complex mirrors.

Concave mirror:

Aka a converging mirror, has a surface that curves inward like the inside of a bowl nd causes parallel rays to come to a focus.

More curved vs less curved:

More curved = focus is clearer

Less curved = focus is farther

C (Centre of the curvature):

Centre of the sphere/cylinder from the mirror.

R (Radius of the curvature):

The distance from the centre of curvature to the mirror.

V (The vertex):

Geometric centre of the mirror.

PA (Principal axis):

Line drawn through the vertex perpendicular to the surface.

F (Focus):

Point where light rays parallel to the PA come together or diverge from. Can be real or virtual depending on if light focuses there or appears to.

f (focal length):

Distance from vertex to focus measured along the principal axis.

What does the focal length of a mirror depend on?

How curved the mirror is.

The greater the curvature:

The shorter the focal length.

Real:

Rays drawn in front of a mirror as solid lines.

Virtual:

Rays drawn behind a mirror and shown as dotted lines.

What image can be projected on a screen.

Real images.

Use of flashlight:

To produce a parallel beam (light to spread out/diverge).

Use of telescope:

To collect light from a distant source and focus it for viewing (far light to create an image).

Use of cosmetic mirror:

To produce an enlarged image (makes images appear larger).

Use of headlights of a car:

To produce a parallel beam of light that is directed down or straight ahead (light to spread out/diverge).