[TGO] Rectilinear Propagation of Light

Shadows

• dark image formed by intercepting light rays

point source

• a (blank) blocked by an opaque object will produce a shadow known as Umbra, Total / Absolute / Geometric Shadow.

Umbra

• Latin word which means "shade"

• it is the central uniform dark region of the shadow with sharp boarder.

Penumbra

• derived from Latin word "paene" which means "nearly"

• it is the outer annular region of the shadow with partial illumination.

Umbra
Penumbra

An extended source blocked by an opaque object will form a shadow of 2 regions:

Eclipse

a natural phenomenon which further demonstrates the Law of Rectilinear Propagation of Light.

Region of Illumination

• Allowing light coming from a point source to enter an aperture will cast an image on the second screen.

• Full Illumination of the same shape as the aperture will be formed.

Full Illumination

Partial illumination

if a beam of light coming from an extended source enters an aperture, two regions of illumination will be formed:

Full Illumination

the uniform central region of illumination

Partial illumination

the outer annular region of illumination with partial darkness.

Pinhole Camera

• A lensless device consist of a light tight box of adjustable length and dark interior.

• It was invented by Giambattista de la Porta.

• It is also known as Camera Obscura or Porta's Camera.

In Pinhole Camera

1) The image is real and inverted

2) The clarity of image in pinhole camera depends on the size of the hole

3) There is an optimum size of pinhole for maximum image sharpness

4) The size of the image depends on the length of the camera

5) There is a large depth focus

6) The illumination of the image is very low compared to that of a camera having a len

7) The image is free from distortion

Similar Triangles

• used to solve problems involving rectilinear propagation of light.

• they are pair of triangles which share a common apex, wherein one triangle is photographic enlargement of the other