Unit 2 - Optics

Chapter 5 Optical systems make use of mirrors and lenses.

5.1 The Ray Model of Light


5.2 Concave Mirrors page 185

A mirror that is curved inward is called a concave mirror. Since the concave mirrors have a curved surface, it reflects light in a unique way. Parallel rays bounce off the mirror and meet at a point called the focal point. This action is called converging. Depending on how far the image is from the focal point, an image is formed. For example, if you are staring at a spoon, if you look at it further away, your body becomes smaller but upside down. When it comes closer, your body remains upside down but much larger. When the distance between the spoon and your body is between the focal point, you become larger than you actually are and upright. Concave mirrors are used in many ways. If a light is shining at the focal point of the mirror, all the light rays bounce off the mirror and are reflected parallel to each other. This makes a very strong beam of light. Used do car lights, and flash lights use this mirror. High-performance telescopes also use the concave mirror so that it can focus on small details. Large telescopes use concave mirrors so the mirror gets light and it concentrates on light effectively.
Questions
Answers
1. What is a concave mirror?
It is a mirror that curves inward.


2. What do you call the point where parallel light rays bounce off the curved surface of a concave mirror and then meet at a single point?
The point is called a focal point.


3. Describe the meaning of converging in the optical term?
Converging is light rays that are coming together at a focal point.
external image 3-2.jpg external image concave_mirror.jpg
Questions
Answers
4. What does the image formed by a concave mirror depend on?
IT depends on how far the object is from the focal point of the mirror.


5. True or False? If a distant object is reflected in a concave mirror, its image is big and upside down.
False.


6. As the object approaches the focal point, what happens to its image?
The image is inverted but gets bigger.
external image hsc_as3.gif
Questions
Answers
7. List at least two uses of concave mirror and explain.
Two uses for a concave mirror is for car lights and flashlights. The light is placed at the focal point, then the light rays bounce off the mirror and reflects parallel to each other. The focussed beam of light is intense.


8. Why does the largest telescopes all use concave mirrors? Explain.
The largest telescope uses concave mirrors because it collects the light, which makes the mirror concentrate on light.


9. Why are shaving and make-up mirrors concave mirrors? Explain.
Shaving and make-up mirrors use concave mirrors because the picture is enlarges the person's face,so it is easier to see small details.