Optics Unit SummaryChapter 10 Light and Reflection

10.1 Sources and Nature of LightSources of Lightwhite light: light from hot objects is made up of many different colours mixed together.

incandescence: light emitted from a material because of the high temperature of the material.

How does an incandescent light bulb work?

An incandescent light bulb has a tiny tungsten wire that gets very hot and glows brightly when electric current runs through it.

electric discharge: the process of emitting light by heating a gas, or vapour, instead of a wire with an electric current.

fluorescence: light that is emitted during exposure of the source to UV (ultra violet) light.

There are two types of light:

o luminous: objects that emit their own light (sun) o non-luminous: objects that do not emit light (flashlight that is switched off)

luminescence: the emission of light by a material or an object that has not been heated.

Types of luminescence- fluorescence- phosphorescence- chemiluminescence- bioluminescence

phosphorescence: light that is emitted due to exposure of the source to UV light, and that continues to be emitted for some time in the absence of UV light.

chemiluminescence: light that is produced by a chemical reaction without a rise in temperature.

bioluminescence: light that is emitted by biochemical reaction in a living organism.

Nature of LightLight is the only form of energy that can travel like a wave through empty space and through some materials. Light behaves like a special kind of wave, called an electromagnetic wave.

wavelength: the distance from one crest (or through) of a wave to the next crest (or through).

Electromagnetic waves are invisible and travel through a vacuum. They travel through a vacuum, such as space, at the speed of light (3.00 x 108 m/s).

electromagnetic spectrum: the entire range of electromagnetic waves in order of wavelength and/or frequency.

10.2 Properties of Light and Reflection

reflection: the change in direction of a light ray when it bounces off a surface.

medium: the substance through which light travels.

ray: a straight line with an arrowhead that shows the direction in which light waves are travelling.

incident ray: a ray of light that travels from a light source toward a surface.

angle of incidence: the angle between the incident ray and the normal in a ray diagram. (i)

normal: a line that is perpendicular to a surface where a ray of light meets the surface.

reflected ray: a ray that begins at the point where the incident ray and the normal meet.

angle of reflection: the angle between the reflected ray and the normal in a ray diagram. (r)

plane mirror: a mirror with a flat, reflective surface.

virtual image: an image formed by rays that appear to be coming, from a certain position, but are not actually coming from this position; image does not form a visible projection on a screen.

In general, an image has four characteristics:

- size (same size, larger than, or smaller than object)- attitude ( upright or inverted)- location ( closer than, father than, or the same distance as the object)- type (real image or virtual image)

Characteristics for an image formed in a plane mirror:

- it is the same size as the object- it is virtual- it is laterally inverted

- it is upright

KEY CONCEPT- Incandescence is light that is emitted from an object because the object is very hot.

- Luminescence is light that is emitted in the absence of heat. Fluorescence, phosphorescence, chemiluminescence, and bioluminescence are all forms of luminescence.

- Light is transmitted in the form of electromagnetic waves. Visible light makes up only a small part of the electromagnetic spectrum.

LAWS OF REFLECTION

1. The incident ray, the reflected ray, and the normal always lie on the same plane.2. The angle of reflection, ∠r, is equal to the angle of incidence, ∠i.∠r = ∠i

SALT

- it has the same distance as the object

10.3 Images in Concave Mirrors

concave mirror: a mirror whose reflected surface curves inward.

principal axis: on a concave mirror, the line that passes through the centre of curvature,C, of the mirror and is normal to the centre of the mirror.

focal point: the point on the principal axis through which reflected rays pass when the incident rays are parallel to and near the principal axis.

focal length: the distance between the vertex of a mirror and the focal point.

An Object between the Focal Point and the Mirror

An Object between the Focal Point and the Centre of Curvature

An Object beyond the Centre of Curvature

spherical aberration: irregularities in an image in a curved mirror that result when reflected rays from the outer parts of the mirror do not go through the focal point.

10.4 Images in Convex Mirrors

convex mirror: a mirror whose reflecting surface curves outward.

Chapter 11 Refraction