Geometrical Optics in Physics for Engineering Students

Geometric Optics

1. Geometric Optics

2. •Uses wave model of light to explain
properties such as reflection and refraction
•Assumptions of geometric optics
- light travels in straight lines
- ray: path taken by light

3. Pinhole Camera
•Simplest version of a camera consisting of
a box with a small opening
•Light ray passing from the top of an object
go through the hole and hit the back of the
box
•Light ray passing from the bottom of the
object go through the hole and hit the back

5. Image Characteristics
•Real Image – can be formed on a screen;
not virtual
•Image smaller than object
•Image is inverted
•If photographic film placed on the back of
the box, picture is permanent

6. Equation
h
i = d
i
h
o d
o
h
i - height of image
d
i – distance of image
h
o – height of object
d
o – distance of object

7. Magnification (M)
M = h
i
h
o
If M > 1, image is enlarged
If M < 1, image is reduced

8. Example

9. Reflection
•When light rays hit an opaque (not
transparent) surface, they are reflected
•Law of Reflection
angle of incidence =
angle of reflection
i = r

10. normal
ir

11. Diffuse Reflection
•When light reflected from uneven surfaces
reflect in many directions (no image can
form)

12. Images
•When parallel rays of light are reflected
parallel, an image can form
•Image formed is virtual (not real) and
appears at the same distance behind the
mirror as the object is in front (d
i = d
o)
•Image formed is the same height as the
object (h
i = h
o)

13. Brains Role
•Light ray from the object hits the mirror
and reflects to the eye
•Brain assumes that light travels in a
straight line so we believe the reflected
light originated somewhere behind the
mirror

16. Image Characteristics
•Virtual
•Same size
•Erect
•Laterally inverted