Physics: Light Behavior (Waves)

Law of Reflection

The angle of reflection is equal to angle of incidence.

Law of Reflection

The incident ray, reflected ray and normal at points of incidence all lie on the same plane.

Normal Ray/ Line

is the imaginary that is perpendicular to the plane.

Total Internal Reflection

When the incident angle is greater than critical angle, light is totally reflected.

Critical Angle

angle of incidence in denser medium for which angle of refraction is 90 degrees.

Characteristics of Image formed frome Plan Mirror

• Image are virtual (cannot be located with a screen)

Plane Mirror Image

• Image is same size as object

Plane Mirror Image

• Image is same distance inside the mirror

Plane Mirror Image

• Image is upright

Plane Mirror Image

• Image is laterally inverted

Law of Refraction

The sine of the angle of incidence over the sine of angle of reflection is a constant.

sin i/ sin r = constant = refractive index (n)

• Also known as Snell’s Law

Law of Refraction

The incident ray, reflected ray and normal at the points of incidence all lie on the same plane.

Real Images

produced at a point to which light rays converge.

Virtual Images

produced at a point from which light rays appear to diverge.

Examples of real images:

• image produced on the retina

• image produced in a camera

• image produced on the screen at the cinema

Examples of virtual images

• image produced in a mirror

• image produced by a convex lens acting as a magnifying glass

• image produced by a concave lens

Features of real images formed by lenses

• can be formed on a screen

• are produced by the conv

Features of virtual images formed by lenses

• cannot be formed on a screen

• are produced due to the divergence of rays

• are located on the same side of the lens as the object

• are erect

When light enters a second medium perpendicular to its interface:

• it does not deviate - the angles of incidence and refraction are both zero.

• its speed is greater in the less optically dense medium.

When light enters a more optically dense medium other than perpendicularly:

• it refracts towards the normal, that is the angle between the ray and the normal decreases

• its speed decreases

Absolute Refractive Index

n = vacuum (c)/ medium (v)

Refractive Index is unitless

• Absoulute Refractive Index > 1

• Relative Refractive Index =< 1 or > 1, never = 1

Optical Density

measured by refractive index of a medium.

Refractive Index = Optical Density

Relative refractive index

compares two media’s light speeds.

Light Speed in vacuum

• is 3×10³ m/s

Refractive Index in Greater Medium

• is