SCPY152 General Physics IILecture 1 Ray Optics

Udom Robkob, Physics-MUSCJune 15, 2015

Today Topics

• Nature of light• Light rays• Law of light reflection• Law of light refraction• Image formation• Images from mirrors• Images from refractive surfaces

Nature of Light

• Visible light is electromagnetic waves, in the range of wavelength 400 – 700 nm

• Light travel in empty space at speed of co = 3x108 m/s

• In medium light speed is lower to be c, according to electromagnetic properties of the medium. The ratio co/c = n is known as refractive index of the medium

Nature of Light

Nature of Light

• 4 basic properties will be studied in the following categories:– Reflection and refraction ray optics– Interference and diffraction wave optics

Light Rays

• Defined from light path from the source• At a distance far from the source, the rays are

approximately parallel and will represented with a single ray

Light Reflection

• Determine reflection of light from smooth reflective surface;

Light Reflection

• Since abc = abd 1 = ’1 “law of light reflection”

Light Reflection

• Double reflections

Light Refraction

• Determine light refraction at smooth refractive surface

Light Refraction

• Law of light refraction

0 111 1

0 222 2

1 2

2 1

/tan sin

/tan sin

sin "Snell's law"

sin

n

ab abn

ab abn

n

Light Refraction

• Nature of refraction

Light Refraction

• Off set from thin slab

Light Refraction

• Measuring refractive index of prism, apex angle is

Light Refraction

• Criterion: min

Critical Angle

• Total internal reflection – critical angle

Water-to –air system

Brewster’s Angle

• Brewster’s angle

Image Formation

• Pinhole camera

Images from Mirrors

• Mirror specification (let light comes from the left hand side)– Plane mirror– Curved mirrors• Concave mirror• Convex mirror

Images from Mirrors

• Image of point object

Images from Mirrors

• Image magnification

Mirror image equation

Images from Mirrors

• Image magnification Focal point/length

Mirror image equation

Images from Mirrors

Images from Mirrors

Images from Mirrors

Images from Refractive Surface

• Refractive surfaces– Convex surface– Concave surface

Images from Refractive Surface

• Image of point object

Images from Refractive Surface

• Cont.

Image equation

Images from Refractive Surface

• Flat refractive surface – appearing depth

Images from Refractive Surface

• Concave refractive surface – appearing depth

Images from Refractive Surface

• Image magnification – from equivalent triangles, we have

1

2

n qy y y q RM

p R q R y p R n p

Images from Refractive Surface

• Revisited previous example – what is the image magnification of the coin.