Copy of 03 - Laser Reflection - Gizmo PDF

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The image you see is called a virtual image because no actual light rays are focused there. The dotted lines represent locations from which light appears to be coming to an observer located left of the lens. An observer would perceive a magnified virtual image of the candle. This is what happens whe...

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Student Exploration: Laser Reflection Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: angle of incidence, angle of reflection, laser, law of reflection, plane mirror, reflection Prior Knowledge Questions (Do these BEFORE using the Gizmo.) READ THIS and answer the Prior Knowledge Questions 1-5 1. Define the following: a) Light Ray:

A light ray is a line (straight or curved) that is perpendicular to the light's wavefronts; its tangent is collinear with the wave vector

b) Geometric Optics:

model of optics that describes light propagation in terms of rays

c) Incident light:

light that falls on a subject

2. Compare the three types of objects and what happens to light when it hits it: d) Transparent:

Light passes through

e) Translucent:

Allow some light to pass through

f) Opaque:

No light passes

3. Is each object translucent, transparent or opaque a textbook

Opaque

frosted glass

Translucent

clean air

Transparent

a clean sheet of glass

Transparent

sunglasses

Translucent

a rock

Opaque

apple juice

Transparent

a single sheet of thin tissue paper

Translucent

Imagine you shine a flashlight directly at a mirror, as shown below. 4. Click the image, click Edit Draw an arrow showing the direction you think the beam of light will most likely reflect off the mirror. Double click image

5. Click the image, click Edit Suppose you tilt the mirror. Draw an arrow showing the direction the beam will most likely reflect off the mirror now.

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Gizmo Warm-up Flashlights produce wide beams of light that have various wavelengths. A laser, on the other hand, is a narrow beam of light with only one wavelength. All the waves in a laser beam are parallel to one another. As a result, lasers are ideal for studying reflection, or how waves bounce off a surface. Using the Laser Reflection Gizmo, you can adjust the position of a laser beam and mirror to study how light behaves when it is reflected. 1. Drag the Angle slider back and forth. Describe what happens to the reflected laser beam: The laser bar is reflected at an alternate point. At the point when the point slider is moved to one side, the laser shaft is reflected at a negative angle, when the slider is moved to the right the laser is reflected to a positive point

2. Drag the laser up and down. Describe what happens to the reflected laser beam: The point where the laser is reflected moved

Activity A: Reflection from a plane mirror

Get the Gizmo ready: ● Set the Laser location to 0 cm. ● Set the Angle to 25 degrees. ● Make sure Plane mirror is selected.

Introduction: A plane mirror is a perfectly flat, smooth surface. In this activity, you will study how plane mirrors reflect light. Question: How does the angle of a mirror determine the angle of the reflected light? 1. Observe: Turn on Show normal. The normal is the dotted line perpendicular to the mirror. The angle of incidence (θi) is the angle between the incoming laser beam and the normal. The angle of reflection (θr) is the angle between the reflected laser beam and the normal. Move the Angle slider back and forth. What do you notice about the sizes of θi and θr? θi and θr grew and shrunk, but always stayed the same size as each other 2. Measure: Set the Angle to 40 degrees and turn on the Show protractor. Each marking on the protractor represents 10 degrees.

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What do θi and θr equal?

θi =

θr =

40°

40°

3. Make a rule: What is the relationship between θi and θr? They are equal Turn on Show angles and move the Angle slider back and forth. Was your rule correct? Yes, it was correct The law of reflection states that the angle of incidence is equal to the angle of reflection. 4. Gather data: Use the Gizmo to complete the table below. Mirror angle

Angle of incidence (θi)

Angle of reflection (θr)

0°

0°

0°

25°

25°

25°

50°

50°

50°

5. Make a rule: How is the mirror angle related to the angles of incidence and reflection? The mirror angle is the same as the angles of incidence and reflection.

Activity B: Reflection from non-planar mirrors

Get the Gizmo ready: ● Turn off Show normal and Show protractor. ● Set the mirror Angle to 50°.

Question: How can you use the angle of refraction to determine the shape of a non-planar mirror’s surface? 1. Observe: Turn on Insert beam splitter. How do the seven incoming beams compare with one another? How do the reflected beams compare with one another? The incoming beams and reflected beams are both the same width apart from each other 2. Observe: From the dropdown menu at lower right, select Mirror 1. Unlike the plane mirror, mirror 1 is not flat. A. Describe how the laser beams changed:

They are now different widths apart and reflect at different angles

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B. Why do you think this happened?

Because the mirror’s surface isn’t flat

3. Solve: Turn off Insert beam splitter. Set the mirror’s Angle to 0 degrees and the Laser location to 35 cm. Check that Show angles are on. A. What are the angle of incidence and angle of reflection (θi and θr)? They are both at 3.5°

B. What does this tell you about the surface of the mirror in this location? That the mirror is angled down

C. Move the Laser location to 14 cm. How did the orientation of the beam change? It changed by reflecting upwards

D. What does this tell you about the surface of the mirror in this location? That the mirror is angled up

4. Summarize: What does it mean if the reflected beam is above the incident beam? What does it mean if the reflected beam is below the incident beam? If the reflected beam is above the incident beam, the surface it’s reflecting off of is angled upwards. If the reflected beam is below the incident beam, it means the surface it’s reflecting off of is angled downwards.

5. Collect data: You will now use the laser to map the surfaces of mirrors 1, 2, and 3. In the rows of the table, record each mirror’s angle at all the listed locations. If the beam is deflected downward, the angle is negative. Otherwise the angle is positive. Double-click to open in Google Draw

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Height

Mirror 1 Angle

Mirror 2 Angle

Mirror 3 Angle

35 cm

-3.5

3.8

0

30 cm

-5

2.5

5

25 cm

-3.5

3.8

0

20 cm

0

2.5

-5

15 cm

3.5

1.3

0

10 cm

5

0

5

5 cm

2.5

-1.3

0

0 cm

0

-2.5

-5

-5 cm

-3.5

-3.8

0

-10 cm

-5

-5

5

-15 cm

-3.5

-3.8

0

-20 cm

0

-2.5

-5

-25 cm

-3.5

-1.3

0

-30 cm

-5

-2.5

5

-35 cm

-3.5

-3.8

0

Mirror 1

Mirror 2

Mirror 3

6. Analyze: Does the law of reflection hold true for mirrors that aren’t flat? Use the Gizmo to explore this question, and describe your findings. Yes, it still applies to mirrors that aren’t flat. The laser hits a small point in the mirror, so even if the mirror is curved, the place where the laser beam reflects is flat 7. There are actually two laws of reflection. READ THIS and state the Second Law of Reflection: The incident ray, the reflected ray, and the normal all lie in the same plane.

8. What is the difference between specular reflection and diffuse reflection? Provide some examples of both: Specular reflection is reflection of light off a smooth surface, diffuse reflection is reflection of light off an irregular or dull surface. Some examples of specular reflection are bodies of water, mirrors or glass. Some examples of diffuse reflection are bicycle reflectors and disco balls.

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9. a) If you were painting the walls in your classroom, would you want the walls to exhibit specular or diffuse reflection? Explain. b) Given your choice, should you use gloss or matte paint? Diffuse reflection so that light reflects in all parts of the classroom, and is not too blinding. Matte paint would be a better choice.

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