Module 5

1. Module 5

1.15. Page 4

Lesson 3

Module 5—Wave Theory of Light

Read

Read pages 658–659 of your textbook for more explanation and help drawing ray diagrams. Note that in the textbook, the ray through the vertex is replaced with a ray through the centre point.

The Mirror Equation

Ray diagrams are a useful tool for revealing image characteristics using the law of reflection and basic geometry. This same tool can also be used to derive a mathematical equation for finding and identifying image characteristics. The derivation of the mirror equation can be seen on pages 661–662 of your textbook.

The mirror equation relates the focal length of a curved mirror to the image and object positions.

Expressed as an equation, it is as follows:

Quantity	Symbol	SI Unit
object position relative to the vertex	do	m
image position relative to the vertex	di	m
focal length	f	m

The image and object characteristics are also described in these equations using sign conventions.

Positive distances describe real images and objects.
Negative distances describe virtual images and objects.
Converging mirrors have a real focal length that is positive.
Diverging mirrors have a virtual focal length that is negative.

Magnification is the ratio of the image height to the object height. A negative sign is used to accommodate the preceding sign conventions.

Negative height describes an inverted image or object.
Positive height describes an upright image or object.

	Quantity	Positive if	Negative if
Attitude	h	erect	inverted
Image Type	d	real	virtual
Mirror Type	f	converging (convex)	diverging (concave)

Note: If the image type is real, the mirror type must be convex.

Read

See “Example 13.2” on page 664 of the textbook for an example of how to use the mirror equation.

Module 5: Lesson 3 Assignment

Remember to submit your answers to A 1, A 2, A 3, A 4, and A 5 to your teacher as part of your Module 5: Lesson 3 Assignment.

A 1. Complete “Concept Check” questions 1 and 2 on page 662 of your textbook.

A 2. A converging mirror has a focal length of 20 cm. The object is placed 30 cm in front of the mirror. Where will the image appear?

A 3. A diverging mirror has a focal length of 0.12 m. The image is located 0.070 m from the mirror. Where is the object located?

A 4. A student places a 5.0-cm-tall object 15 cm away from a converging mirror. The image is 12 cm from the mirror. What is the height and orientation of the image?

A 5. A 1.5-cm-tall object is placed 12 cm away from a converging mirror. The image is magnified to four times its original height and is inverted. What is the mirror’s focal length?

Discuss

The Newtonian telescope is also known as the poor man’s telescope. It is a reflecting telescope that was invented by Sir Isaac Newton in 1689. It consists of a large tube open at one end with a large converging mirror at the opposite end. Light from a distant object enters the tube and is reflected from the surface of the large, concave, primary mirror. The reflected light is then incident on a small, flat, secondary mirror that redirects the light into an eyepiece for viewing. The geometric location of the secondary mirror is related to the curvature of the primary mirror.

Module 5: Lesson 3 Assignment

Remember to submit your answer to D 1 to your teacher as part of your Module 5: Lesson 3 Assignment.

D 1. Work with another student to determine where, exactly, the secondary mirror should be placed so that the telescope produces a clear image of the distant object. Use a ray diagram to answer this question, and design an experiment to determine the focal length of the large, primary mirror. Your design should include the problem, prediction, materials, procedure, and analysis required to answer the problem.

Discussion Scoring Guide

Discussion Scoring Guide

Principles involved: scientific method, lab procedures, reflection, and ray diagrams
Criteria	Level 1 (Below Standard)	Level 2 (Approaching Standard)	Level 3 (Standard)	Level 4 (Above Standard)
Knowledge
Demonstrates understanding of the situation, physics principles and technology, and their connections.	Demonstrates a vague and sometimes incorrect understanding of the physics principles involved. Obvious irrelevant or missing information.	Demonstrates a basic understanding of the physics principles involved. May exhibit minor mistakes or vague information or application to the situation.	Demonstrates a good understanding of the physics principles involved and applies them properly to the given situation. All necessary information is given.	Demonstrates a superior understanding of the physics principles involved and their application to the situation. All applications are considered in detail.
Reflection
The post shows reflection on one’s own and other students’ work. Contributes to the group discussion.	Does not make an effort to participate. Seems indifferent to discussion.	Occasionally makes meaningful reflections on the group’s efforts or discussions. Marginal effort is shown to become involved with the group or discussion.	Frequently makes meaningful reflections on the group’s efforts and presents relevant viewpoints for consideration by the group. Interacts freely with group members.	Regularly attempts to motivate the group discussion and delve deeper into concepts. Interacts freely and encourages all group members.
Content and presentation of discussion summary
The information is logically arranged in a clear and concise manner.	The information is poorly organized with many concepts implied. Irrelevant or rambling sentences make reading difficult.	The information is somewhat organized with implied concepts. Excessive words or awkward sentences are used, which hinders reading.	The information is well-organized and logically arranged. All concepts are explicitly explained. There are a few awkward but understandable sentences.	The information is well-organized and very easy to understand. Well-worded sentences make reading pleasurable.