Spherical Mirrors – Learning Outcomes  Recognise and use key words relating to mirrors.  Centre of curvature  Focus / focal point, focal length  Pole  Principal axis  Use ray tracing to demonstrate reflection.  Find images in spherical mirrors using ray tracing.  Describe the images formed in spherical mirrors.  Differentiate between real and virtual images. 1

Spherical Mirrors – Learning Outcomes 2

Spherical Mirrors - Images  Unlike in a plane mirror, spherical mirrors can form both real and virtual images.  Real images are formed by the actual intersection of rays  They can be formed on a screen or found by using no parallax  Virtual images are formed by the apparent intersection of rays.  They cannot be formed on a screen, but may be found using no parallax. 3

Spherical Mirrors 4

Concave Mirror – Ray Tracing  A ray striking the pole is reflected at an equal angle with the principal axis. 5

Concave Mirror – Ray Tracing  A ray passing through the centre of curvature will be reflected back through the centre of curvature. 6

Concave Mirror – Ray Tracing  A ray incident parallel to the principal axis will reflect back through the focus 7

Concave Mirror – Ray Tracing  A ray passing through the focus will reflect parallel to the principal axis. 8

Concave Mirrors - Images  To focus an image of a distant object. 1.Use a bright distant object (e.g. a window in a dark room). 2.Face a concave mirror towards the object. 3.Hold a piece of paper or cardboard in front of the mirror, and move it back and forth to focus the image. 4.If the object was very far away, the image will form at the focus of the mirror. 9

Concave Mirrors - Images 1.An object outside the centre of curvature. Image is:  real  inverted  diminished  between C and f 10

Concave Mirrors - Images 2.An object at the centre of curvature. Image is:  real  inverted  same size  at C 11

Concave Mirrors - Images 3.An object between the centre of curvature and the focus. Image is:  real  inverted  magnified  outside C 12

Concave Mirrors - Images 4.An object at the focus. Image is:  nonexistant  at infinity 13

Concave Mirrors - Images 5.An object inside the focus. Image is:  virtual  upright  magnified  behind mirror 14

Convex Mirrors – Ray Tracing 1.A ray which strikes the pole is reflected at an equal angle to the principal axis. 15

Convex Mirrors – Ray Tracing 2.A ray heading for the centre of curvature will be reflected back along its path. 16

Convex Mirrors – Ray Tracing 3.A ray incident parallel to the principal axis is reflected back as if it came from the focus. 17

Convex Mirrors – Ray Tracing 4.A ray travelling towards the focus is reflected parallel to the principal axis. 18

Convex Mirrors - Images  An object anywhere in front of a convex mirror will yield the same result – image is virtual, diminished, upright, and behind the mirror. 19

Formula for Spherical Mirrors 20

Calculations  e.g. Rachel holds a concave mirror 30cm in front of a bulb. How far from the mirror does the image form if the focal length of the mirror is 20cm? 40cm?  e.g. An object is placed 30cm in front of a concave mirror. A real image of the object is formed 50cm from the mirror.  What is the focal length of the mirror?  If the object is 5cm high, what is the height of the image?  e.g. An image is formed in a concave mirror of focal length 20cm. The image is three times the size of the object. Where must the object be placed if the image is real? What if the image is virtual? 21

Uses of Mirrors  Concave – magnify when object inside C  Dentist mirrors  Cosmetic mirrors  Searchlights / floodlights / car headlights  Convex – wide field of view  Door mirror in a car  At concealed entrances  At ATMs and in banks 22