Physics Ch12. - Light waves

Refraction

The bending of a wave and change in speed as it passes from one medium to another

Total internal refraction

It occurs when the angle of incidence is large enough that the angle of refraction becomes greater than 90^o causing the ray to reflect instead inside the material, this happens when going from a more dense to less dense material.

critical angle

when the angle of incidence is large enough that the angle of refraction is equal to 90^o so light travels along the boundary

refractive index

how much light is refracted in a certain medium

what happens to light when it enters a prism at an angle

line bends toward the normal and changes it speed ( slows down ), because the prism is denser than air

2 properties that all waves have (light )

• transfer of energy

• can be reflected

• can be refracted

• have a wavelength/ frequency

• all tranverse waves

state the colour of the rainbow that refracts the most and why

violet, has a shorter wavelength and therefore higher refractive index meaning it bends towards the normal more and travels at a slower speed

what side of electromagnetic wave spectrum has shorter wavelengths and higher frequency and therefore travels slower

gamma rays

speed of light

3 × 10⁸

Practical - measure refractive index of glass

• Place the rectangular box in the centre of a plain piece of paper and draw round it

• remove the glass block

• mark a point in the middle of one of the long sides. This will be the target

• draw the normal passing through the target

• measure your first angle of incidence using a protractor and draw the incidence ray using a ruler

• using the laser board direct a beam along the drawn ray

• replace the glass block

• mark several points along the exit beam

• remove the block and draw the exit ray, then draw the ray within the block by joining the rays ( include arrows )

• measure the angle of refraction and write down result table

• repeat the experiment for a variety of angles of incidence

• use calculator and equation… to find n

what are some uses of prisms

• quality optical equipment - better quality then mirrors

• small prism to reflect light in, Hi-Viz jackets and bicycle reflectors

optic fibre

• total internal reflection is used to reflect light along optic fibres which can be used for communications, endoscopes and decorative lamps

• light travelling down an optic fibre reflects every time it touches the edge of the fibre.