Reflection and Refraction

Reflection

The law of reflection, ray diagrams, and images formed by plane mirrors

Reflection lesson illustration

Review

Can you name this wave phenomena?

 

 

 

 

 

 

 

Interference or beats

 

 

Show Me The Physics
YouTube Channel

 

Reflection Notes

 

B. Reflection

 

 

 

 


Reflection lesson illustration

[ Reflection ]

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1. Law of Reflection

Reflection lesson illustration

a.  θ of incidence = θ of reflection

 

 

Reflection lesson illustration

[ θin = θref ]

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showmethephysics.com

 

 

 

Use the acute angles on your protractor /p>

Reflection lesson illustration

Charles William Weick Elementary Mechanical Drawing, Theory and Practice
(New York: McGraw-Hill Book Company, 1915) 21

ETC Clipart  | Protractor

Line going through O, we will
 refer to as the baseline 

 

 

 

 

 

Reflection lesson illustration
θin = θincidence
(angle incoming normal ray
 makes with the normal)

θref = θreflect
(angle reflected light makes with the normal)



Ray Diagram  - Reflection

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Reflection lesson illustration

 

 

 

 

 

Remember ...

Reflection lesson illustration


... reflection always makes a V

 

 

 

 

What is the smallest mirror
you need to see your whole body?

Reflection lesson illustration

 

 

Reflection lesson illustration

 

1/2 your height

 

 

Click and Drag Gecko 

[ Flash ]

 

The image from a plane mirror:

 

 

a. Virtual (realistic) & Upright (Straight up and down)

 

[ Flash ]

Reflection lesson illustration

 

 

 

 

 

 

Reflection lesson illustration

 

 

b. Incident ray, normal line, and reflected rays are all in the same plane

 

Reflection lesson illustration

Source: Elroy M. Avery School Physics (New York: Sheldon and Company, 1895) 77 

Clipart ETC

 

c. The distance the object is in front of the mirror equals the distance the image is behind the mirror

 

 

2. Two Basic Kinds of Reflection

Reflection lesson illustration 


a. Regular Reflection – reflection off a polished surface (produces images)

Reflection lesson illustration

 

Regular Reflection Produces Images

Reflection lesson illustration

http://www.freeimages.co.uk/

 

b. Diffuse Reflection – reflection off an irregular surface causing light to scatter (no image)



Reflection lesson illustration

 

 

 

Reflection lesson illustration 

 

 

Which letter correctly

shows reflection?

 

 

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Ray C

 

 

 

 

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Angle of Reflection?

 

Reflection lesson illustration 

June 2009

 

 

 

 

 

 

60 degrees
(Angle from normal)

 

Dr. Carlson - Purdue University

 

 

Explore: Beyond Flat Mirrors

The law of reflection also works on curved mirrors — it just makes some interesting images.

Drag the orange object. Switch between concave and convex mirrors.

More: Lenses & Mirrors lessons

Check Your Understanding

5 quick questions — pick an answer to see if you’re right.

1. When using the law of reflection, the angles of incidence and reflection are measured from which line?

2. A light ray strikes a plane mirror making a 20° angle with the mirror's surface. What is the angle of reflection?

3. Which best describes the image formed by a plane mirror?

4. A student is 1.6 m tall. What is the shortest plane mirror she needs to see her whole body?

5. Why can't you see your reflection in a sheet of paper, even though it reflects light?

NYSSLS Regents Practice · Waves · Reflection

Designing a Periscope

A periscope uses two flat mirrors, each tilted at 45°, to let a viewer see over a wall. Light from an object strikes the top mirror and reflects down to the bottom mirror, which reflects it into the viewer’s eye.

Light strikes the top mirror at an angle of incidence of 45° (measured from the normal). What is the angle of reflection?

▶ Want a challenge? Open 6 more Regents-style questions  (harder · mixed formats)

Challenge score: 0 / 6

Determine the value

C1. A ray strikes a plane mirror making an angle of 30.° with the surface of the mirror. Determine the angle of reflection, measured as it should be.

θr = °
Multiple choice

C2. A person stands 2.0 m in front of a plane mirror. Where does her image appear?

Support or Refute · Justify

C3. A student makes the following claim.

Claim: If the angle of incidence on a plane mirror increases by 10.°, the angle between the incident ray and the reflected ray also increases by 10.°.

Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.

Draw the vector · Determine the magnitude

C4. In the periscope, light from the object travels horizontally to the right and strikes the top mirror. Choose the direction of the velocity of the light after it reflects from the top mirror, and determine its speed (in air, about the same as in a vacuum).

light
●
v = × 108 m/s
Multiple choice

C5. Why can you see your reflection in a mirror but not in a sheet of white paper, even though both reflect light?

Constructed response

C6. A student builds a periscope but tilts the top mirror at 30.° to the horizontal instead of 45°. Using the law of reflection, explain why light traveling horizontally into the periscope would no longer travel straight down the tube.

Refraction →