Light: Reflection and refraction

Light

Electromagnetic radiation that can be detected by the human eye. It is a form of energy. It has a wavelength between 700nm (red) and 400nm (violet)

A self luminous object

Produces its own light e.g the Sun, stars. A non-luminous object does not produce its own light - it reflects light from its surface which makes it visible.

Reflection of light

The bouncing of light off the surface of an object

Laws of reflection (1)

The incident ray, the normal and the reflected ray all lie in the same plane.

Laws of reflection (2)

The angle of incidence equals the angle of reflection

Parallax

The apparent movement of one object relative to the other due to the motion of the observer. The object that is furthest away appears to move with the observer.

A real image

Formed by the actual intersection of light rays

Refraction

The bending of light as it passes from one optical medium to another

A virtual image

Is formed by the apparent intersection of light rays

Laws of refraction (1)

The incident ray, the normal and the refracted ray all lie in the same plane

Laws of refraction (2)

The sine of the angle of incidence is proportional to the sine angle of refraction, for a given pair of media (snells law)

Refractive index

Of a substance is the ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from air into the substance

The critical angle (C)

The angle in the denser of two media when the angle in the less dense medium is 90°

Total internal reflection

When the angle of incidence in the denser of two media exceeds the critical angle and light is reflected back into the medium

Optic fibre

A very thin strand of transparent material through which light travels by total internal reflection

The power of accommodation

Of the eye is its ability to focus on objects at different distances by changing the shape of the lens

Lens

A piece of carefully cut transparent material that allows light through it

Power of a lens

Is the reciprocal of its focal length

P=1/f

Power of two lenses in contact

Is the sum of their individual powers

Magnification of an image

The ratio of image distance to object distance

Mag = v/u