LIGHT CH. 18. What is Light? Light is an electromagnetic wave that travels through space requiring no medium.

LIGHT

CH. 18

What is Light?

• Light is an electromagnetic wave that travels through space requiring no medium.

What happens to light when it strikes a surface?

• Light can be reflected, transmitted, or absorbed

Distinguish between

• Opaque

• Transparent

• Translucent

•Opaque – Reflects or absorbs all of the light that strikes it. You cannot see through opaque materials.

•Transparent – Transmits most light that strikes it. As light scatters through the substance this allows you to see clearly what is on the other side.

•Translucent – scatters light as it passes through. You can usually see objects on the other side, but the details of the object are blurred.

The Color of Objects

• Opaque objects are the color of the light that is being reflected.

• Transparent and Translucent objects transmit light so the color you see is the color transmitted. Ex. If light passes through stained glass the color you see coming through the glass is the color of the stained glass.

Combining Colors

• Primary colors – three colors combine to make any other color. You have primary colors of light and pigments.

• Secondary colors – equal amounts of two primary colors.

Primary Light Colors

• Red, Blue,Green

• When combined in equal parts they produce white light.

• So the color you see is the color that is being transmitted.

Primary light colors

Primary Pigments

• Yellow, Magenta(red), Cyan(blue)

• When combined in equal amounts they produce black

• So, the color you see is the color that is being reflected.

Primary pigments

• Law of reflection – the angle of incidence, what goes in = the angle of reflection, what comes out

• Focal point – the point through all reflected light rays pass or meet

• Refraction – the bending of a wave due to a change of speed of the medium

• Convex lens – a lens that is thicker in the center than on its edges.

• Electromagnetic wave – no medium required

• Medium – a material in which a wave travels

• Reflection – the process of light striking an object and bouncing off.

• Concave lens – thicker on the edges than in the middle

• Lens – a transparent object with at least one curved side that causes light to bend.

• Focal length – the distance along the optical axis from the center of a mirror to the focal point.

• Light ray – narrow beam of light traveling in a straight line

• Opaque – material such as wood and steel

• Translucent – materials such as wax paper

• Transparent – material such as glass or clear plastic

• Primary colors of light – red, green, blue and when combined make white

• Primary colors of pigment – red, yellow blue, when combined make black

• Microscope –a combination of lenses used to magnify small objects

• Telescope – used to examine very large objects that are far away.

• Camera – uses a convex lens to form an image on a medium.

• Speed of light – 300 million m/s

Reflection and Mirrors

• There are two types of reflection from a surface.

1. Regular reflection – when parallel rays of light hit smooth surfaces

2. Diffuse reflection – when parallel rays of light hit a bumpy or uneven surface

Plane Mirror

• Plane mirrors form a virtual image – an upright image that forms where light seems to come from. A plane mirror produces a virtual image that is upright and the same size as the object.

Plane Mirrors

Concave Mirrors• Ex. Spoon

• These mirrors can form virtual and real images depending how the image falls in relation to the focal point. If the image is farther away from the mirror than the focal point the image is real and appears upside down. If the image is between the mirror and the focal point the image forms a virtual image.

Concave Mirrors

Convex Mirrors

• Can only form a real image. A mirror is curved outward and appears farther away than it actually is.

Convex Mirrors

Refraction and Lenses

• Refraction occurs due to the change of the medium’s speed.

• This creates an index of refraction – a measure of how much a ray of light bends when it enters that material/medium.

Seeing Light

• You see objects when a process occurs that involves both your eyes and your brain

• Convex lenses are used to correct nearsightedness and. Concave lenses are used to correct farsightedness.

Parts of the Eye