light

Laws of reflection

1. Incident ray, reflected ray, and normal at the point of incidence all lie in the same plane

2. Angle of incidence (i) is equal to angle of reflection ( r)

Characteristics of image formed in plane mirror

1. Mirror and obj are equally far from the mirror

2. Mirror image is virtual

3. Mirror image and object are of same size

4. Image is laterally inverted

5. Image is upright

Steps to drawing light diagrams for plane mirror

1. Locate image

2. Draw reflected rays

3. Draw incident rays

Applications of plane mirrors

1. Vision testing

2. Blind mirror corner

3. Instrument scale

4. Periscope

Formula for minimum height of mirror to see full body

½ of height

Virtual image meaning

• image cannot be formed on screen

What is refraction

Bending of light as light passes from 1 optical medium to another

What causes refraction

• due to change in speed of light at boundary of the 2 optical medium

• Optically denser to optically less dense: light bends away frm normal

• Optically less dense to optically denser: light bends away frm normal

Laws of refraction

1. Incident rat, refracted ray and normal all lie in the same plane

2. For 2 given media, ratio of sine of angle of incidence to sine angle of refraction is a constant (sin i / sin r = constant)

Refractive index

Ratio of speed of light in air (vacuum) to speed of light in medium

n= c/v = 3.0× 10^8/v

Speed of light in air/ vacuum

3.0× 10^8

Snells law formula to calculate refractive index (air/ vacuum to medium)

n = sin i / sin r

Principle of reversibility

Light ray wil travel along the same path if its direction of travel is reversed. (Applies to reflection and refraction)

Snells law general formula (medium to medium)

n1sin i = n2sin r

Total internal reflection definition

• complete reflection of a light ray inside and optically denser medium at its boundary with an optically less dense medium

Conditions for total internal reflection (TIR)

1. Light ray travels frm an optically denser medium into and optically less dense medium

2. Angle of incidence in the optically denser medium is greater than the critical angle of the medium

Critical angle definition

Angle of incidence where the angle of refraction in the optically less dense medium is 90*

Formula for critical angle

n medium = 1/ sin c (derived frm snells law)

Relationship btw light intensity, refractive index of medium and critical angle (optical fibre)

• Decreased light intensity.

• Smaller the refractive index, critical angle increases.

• More light loss to surr due to more refraction occurring compared to optical fibre w larger refractive index

Applications of TIR

• glass prisms in binoculars

• Periscopes

• Optical fibres

Uses of optical fibres

• telecommunications

• endoscope

• laparoscope

Advantages of using optical fibres over copper wires in transmission of info

• less distortion

• More info can be transmitted per unit time

Design of optical fibres

• Outer cladding w low refractive index

• Inner core w high refractive index

Relationship btw thickness of lens and focal length

The Thicker the converging lens the shorter the focal length (compared to thinner converging lens of same material

Optical centre definition

Point on the principal axis at the midpoint btw surfaces of converging lens

Principal axis

Line that cuts through the optical centre and is perpendicular to the plane of lens

Principal focus

Point on principal axis where all rays parallel to principle axis meet when passing through converging lens

Focal plane definition

Plane perpendicular to principal axis which all parallel rays meet after passing through the lens

Focal length definition

Distance btw optical centre and focal point

U=inifnity Image Type, distance and uses

• Inverted

• Real

• Diminished

• v = f

• Object lens of telescope

U > 2f image type, distance and uses

• real

• Inverted diminished

• Diminished

• f < v < 2f

• Camera and eye

U = 2f Image type, distance and uses

• inverted

• Real

• Same size

• v = 2f

• Photocopier making same sized copy

f < u < 2f image type distance and uses

• inverted

• Real

• Magnified

• v > 2f

• Projector and photograph enlarger

u = f image type distance and uses

• upright

• Virtual

• Magnified

• Image at infinity (same side of the lens)

• To produce a parallel beam of light

u < f image type distance and uses

• upright

• Virtual

• Magnified

• Image behind object (same side of the lens)

• Magnifying glass

Magnification formula

• Size of image/ size of object

• Image distance/ object distance