1. Mirrors
Reflection of Light

2. Mirrors Word bank MIRROR
Any regular reflecting surface that can produce an image of an object standing in front of it
Common mirrors are made of flat glass painted with silver on one side.

3. Mirrors CHARACTERISTICS OF MIRROR IMAGES A) IMAGE SIZE
Images formed by mirrors can be enlarged, reduced or of the same size as the object forming the image.
Image formed by a plane mirror is of the same size as the object

4. Mirrors
IMAGE SIZE
The apparent reduction in the size of an image as an object moves farther away from the mirror can be explained by the diagram below:
object
Actual image:
same size as the object; same distance from the mirror as the object
image in the mirror as seen by the person (There’s an apparent reduction in size!)

5. Mirrors CHARACTERISTICS OF MIRROR IMAGES B) ORIENTATION
Images formed by mirrors can either be oriented upright or inverted.
Image formed by a plane mirror is always upright.

6. Mirrors CHARACTERISTICS OF MIRROR IMAGES C) NATURE
Images formed by mirrors can either be real (formed in front of the mirror) or virtual (formed at the back of the mirror).
Word bank
VIRTUAL IMAGE
Image formed by light rays that do not converge at the location of the image

7. Mirrors Word bank SPHERICAL MIRROR
Mirror formed from sections of a sphere
Also called a curved mirror
There are two types: the convex mirror and the concave mirror

8. Mirrors Word bank CONCAVE MIRROR
Mirror that curves inward or toward its center
Converges parallel rays of light to a single point called the FOCAL POINT

9. Mirrors Word bank CONVEX MIRROR
Mirror that curves outward or away from its center
Diverges parallel rays of light creating an image behind the mirror

10. Mirrors FEATURES OF THE SPHERICAL MIRROR Spherical mirror R
Principal axis C F f
C – Center of the sphere
R – Radius of curvature: Distance between C the mirror
F – Focal point: Point halfway between C and the mirror
f – Focal length: Distance between F and the mirror; Equal to ½ R

11. Mirrors RAY TRACING METHOD
Method used to describe the location, nature, size and orientation of image formed by a spherical mirror

12. Mirrors
FORMATION OF IMAGE USING
RAY-TRACING METHOD
This process requires tracing of any two rays suggested below:
1) An incident ray from the tip of the object drawn parallel to the principal axis will pass through the focal point upon reflection

13. Mirrors FORMATION OF IMAGE USING RAY-TRACING METHOD
2) An incident ray connecting the tip of the object and the focal point will be reflected parallel to the principal axis
3) An incident ray connecting the tip of the object and the center will be reflected back along the same line

14. Mirrors
The intersection of the reflected rays will form the tip of the image C F
Principal axis
Ray 3
object
Ray 2
Ray 1

15. Mirrors C F Principal axis Ray 3 object Ray 2 incident ray Ray 1
reflected ray

16. Mirrors
Ray 1
For convex mirrors, the focal point and the center are located at the back of the mirror. You have to project the reflected rays back (into the mirror) to locate the intersection.
Ray 3
Ray 2
Principal axis
object F C
incident rays
reflected rays
back projections

17. SEATWORK
An object is placed at different positions in front of a concave mirror. Describe the image formed at each position by completing the table.
Location of object
Location
of image
Nature
Orientation
Size
Between the mirror and the focal point F
At the focal point F
Between the center C and the focal point F
At the center C
Beyond the center C

18. Mirrors MIRROR EQUATION
Another way of locating the images formed by spherical mirrors is by the use of the mirror equation:
focal length, f: distance from the focal point to the mirror
object distance, do: distance from the object to the mirror
image distance, di: distance from the image to the mirror
magnification, m: the number of times the image is larger than the object
height of object, ho
height of image, hi

19. Mirrors SIGN CONVENTIONS
Focal length can be either positive or negative
Focal length is positive for concave mirrors and negative for convex mirrors
Image distance can be either positive or negative
Image distance is positive if the image is real and negative if the image is virtual
Object distance can only be positive
Magnification can be either positive or negative
Magnification is positive if the image is upright and negative if the image is inverted
If the magnitude of the magnification is:
Less than 1, image is reduced
Equal to 1, image is of the same size as the object
Greater than 1, image is enlarged

20. EXAMPLE
An object is 4.00 cm from a concave mirror with a focal length of 10.0 cm. Find the location, size, orientation and nature of the image formed.
Given:
do= 4.00 cm f = 10.0 cm
di= ? m = ?

21. = -6.67 cm (Image is located 6.67 cm from the mirror) m = -di/do
SOLUTION
di = (dof)/(do- f)
= (4.00 cm x 10.0 cm)/(4.00 cm-10.0 cm)
= cm (Image is located 6.67 cm from the mirror)
m = -di/do
= -(-6.67 cm)/(4.00 cm)
= 1.67 (Image is 1.67x larger than the object)
The image is virtual (di is negative), upright (m is positive) and enlarged (magnitude of m is greater than 1)

22. EXAMPLE 2
A girl stares at a shiny Christmas ball with a diameter of 60.0 cm. If her face is 20.0 cm from the ball, describe the location, size, orientation and nature of her image.
The ball is a convex mirror because the center is located inside the ball. Therefore, f is negative. F is half the radius (which is half the diameter).
do= 20.0 cm f = cm
di= ? m = ?

23. = (20.0 cm x -15.0 cm)/(20.0 cm-(-15.0 cm))
SOLUTION
di = (dof)/(do- f)
= (20.0 cm x cm)/(20.0 cm-(-15.0 cm))
= cm (Image is located 8.57 cm from the ball)
m = -di/do
= -(-8.57 cm)/(20.0 cm)
= 0.43 (Image size is 0.43x size of the object)
The image is virtual (di is negative), upright (m is positive) and reduced (magnitude of m is less than 1)

24. HOMEWORK
1) A shaving mirror of focal length 25.0 cm is used by your dad while he shaves 12.0 cm in front of it. How much does the mirror magnify your dad’s face?
2) A convex mirror of focal length 9.0 cm creates an image whose distance is 9.0 cm. Describe the image formed if the object’s height is 5.0 cm.