Ch 15.1 - RefractionCh 15.1 - Refraction

Definition: RefractionDefinition: Refraction

Change in speed of light as it moves from one medium to another.

Can cause bending of the light at the interface between media.

Index of RefractionIndex of Refraction

• The ratio of the speed of light in a vacuum to its speed in a given transparent medium

Index of RefractionIndex of Refraction

speed of light in vacuum

speed of light in medium

n = c/v

n =

Snell’s LawSnell’s Law

n1

n2

1

angle of incidence

2

angle of refraction

n1sin 1 = n2sin 2

nn11 < n < n22

n1

n2

1

2

light bends toward normal

nn11 > n > n22

n1n2

1

2

light bends away from normal

HomeworkHomework

• P567 #1-3 (Snell’s Law)

• P567 #1-3 (Section Review)

15.3 – Optical Phenomena15.3 – Optical Phenomena

DispersionDispersion

The separation of white light into colors due to different refractive indices for different wavelengths.

DispersionDispersionDue to different indices of refraction for different wavelengths of light.

Useful DefinitionsUseful Definitions

• Total Internal Reflection – the complete reflection of light at the boundary of two transparent media

• Critical Angle – the minimum angle of incidence for which total internal reflection occurs

Critical Angle of IncidenceCritical Angle of Incidence

n1

n2

c

Light would refract 90o so it reflects instead, undergoing total internal reflection.

r

n1 > n2

Calculating Critical AngleCalculating Critical Angle

n1sin(1) = n2sin(2)

n1sin(1) = n2sin(90o)

n2 = n1sin(c)

Total Internal ReflectionTotal Internal Reflection

n1

n2

i r

Occurs only when angle of incidence > critical angle

HomeworkHomework

• P582 #1-4, p585 #1-3

15.2 – Thin lenses15.2 – Thin lenses

Lens typesLens types

• Converging – can produce real or virtual images

• Diverging – can produce only virtual images

Ray diagramsRay diagrams

• Same rays as we drew for mirrors

• Rays will always go through the mirror (not reflected) but will be somehow bent (refracted)

Useful DefinitionsUseful Definitions

• Lens – a transparent object that refracts light rays, causing them to converge or diverge to create an image.

• **Big difference with mirrors**– Real is on the right side of the lens. Why?

• + side of mirror is ride side

• - side of mirror is left side

Converging lens #1Converging lens #1

C F

Real, Inverted, Reduced Image

F2F 2F

Converging lens #2Converging lens #2

C F

Real, Inverted, True (Same size) Image

F2F 2F

Converging lens #3Converging lens #3

C F

Real, Inverted, Enlarged Image

F2F

Converging lens #4Converging lens #4

C F

Virtual, Upright, Enlarged Image

F

For converging lensesFor converging lenses

• f is positive• p is positive• q is positive for real images and negative for

virtual images• M is negative for real images and positive for

virtual images • hi is negative for real images and positive for

virtual images

Diverging lensDiverging lens

C F

Virtual, Upright, Reduced Image

F

For diverging lensesFor diverging lenses• f is negative• p is positive• q is negative• M is positive and < 1• hi is positive and < ho

HomeworkHomework

• P576 #1-4