LIGHT: Geometric Optics

The Ray Model of Light

• Light travels in straight lines under a wide variety of circumstances

• Light travels in straight line paths called RAYS

Optical Instruments: Refractive

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th icker in th e m id d le

C O N C A V ED ive rg in g In s trum e ntth in ne r in the m id d le

T h in L en ses

CONVERGING LENS

• Causes parallel rays to converge• Produces real and virtual images.• Focal Length is positive.

Ray Tracing for Converging Lens

Ray 1: Parallel emerge through F

Ray 2: Through F emerge Parallel Ray 3: Straight through center

The Lens Equation

• 1/do + 1/di = 1/f

• m = hi/ho = - di/do – m is magnification

• ho/hi = do/di

DIVERGING LENS

• Causes parallel rays to diverge• Produces only small-virtual images.• Focal Length is negative.

Ray Tracing for Diverging Lens

• Focal length is negative for any diverging instrument.

• Image distance is negative for virtual images.

• Virtual image produced will be smaller than object.

Angular Magnification

Who invented the telescope?

Refracting Telescope

Compound MicroscopeThe eyepiece is placed such that the image formed by the objective falls at first focal point of the eyepiece. The light thus emerges as parallel rays.

Can you explain this?

Total Internal Reflection

• Red light is incident on the glass-air boundary at an angle greater than the critical angle.– although red, when compared to blue and yellow, has

the lower index of refraction.

Can you explain this?

• The pattern formed is from a converging lens.

Spherical Aberation

Chromatic Aberration

• Each color has a different focal point.

• The refractive index is different for each wavelength.

Reflection

• Law of Reflection– The angle of incidence

equals the angle of reflection

• The incident and reflected rays lie in the same plane with the normal to the surface

Diffuse vs Specular Reflection

• Diffuse Reflection– Light incident upon a

rough surface

– Law of reflection still holds; Normals not ll.

• Specular Reflection– Mirror like reflection

– All Normals are parallel

Image formation by a Plane Mirror

• Image distance equals the object distance.

• Image size equals the object size.

• Virtual image formed.

Optical Instruments: Reflective

C O N V E XD ive rg in g In s trum e nt

C O N C A V EC o n ve rg in g Ins trum e nt

S P H E R IC A L M IR R O R S

CONVEX MIRROR

• Produces only small-virtual images.

• Focal Length and Radius are negative.

• Anti-Theft, Rear-View, Safety

CONCAVE MIRROR

• Produces both Real and Virtual Images– Real images can be magnified or reduced

– Virtual images are always magnified.

Real image formed by Converging Rays

Virtual image formed by Diverging Rays

CONCAVE MIRROR

• Real Virtual– Real images can be magnified or reduced

– Virtual images are always magnified.

Equations to Apply

• f = r/2– f is focal length

– r is radius

• ho/hi = do/di – h is height

– d is distance

– o is object

– i is image

• 1/do + 1/di = 1/f

• m = hi/ho = - di/do – m is magnification