Seeing Things

Putting Things Together

Periscopes, Hinged Mirrored & Kaleidoscopes

1) Where exactly are the images in a periscope AND how do light rays reach the Eye-Brain from the object?

Periscopes

Find the first image (Image 1) in the top mirror using equal perpendicular distances . You have to extend the mirror to locate the image.

Images can act like objects. Find the second image in the bottom mirror the same way, but this time use Image 1 as the new object.

The Eye-Brain sees the second image in the bottom mirror as usual. Rays of light appear to come straight from it.

Light rays cannot travel through the opaque bottom mirror. They must have come from the object (Image 1) and reflected off the mirror.

The light rays cannot travel through the opaque top mirror. They must have come from the real object and reflected off the top mirror.

Your TurnAttempt the Questions on

L5 Putting Things Together-Student Notes

Periscopes

Periscopes2) Where exactly are the images in a reversed

periscope AND how do light rays reach the Eye-Brain?

Find the first image (Image 1) in the top mirror using equal perpendicular distances . You have to extend the mirror to locate the image.

Images can act like objects. Find the second image in the bottom mirror the same way, but this time use Image 1 as the new object.

The Eye-Brain sees the second image in the bottom mirror as usual. Rays of light appear to come straight from it.

Light rays cannot travel through the opaque bottom mirror. They must have come from the object (Image 1) and reflected off the mirror.

The light rays cannot travel through the opaque top mirror. They must have come from the real object and reflected off the top mirror.

3) Using images as objects can explain and predict the number of images formed when mirrors are joined at angles.

Finding Images in Mirrors Hinged at 90°

Find the first image (Image 1) in the bottom mirror using equal perpendicular distances .

The top mirror forms an image (Image 2) in the bottom mirror.

The image of the top mirror (Image 2) acts like a mirror. Use Image 1 as the object to find Image 3.

The bottom mirror forms an image (Image 4) in the top mirror.

Image 5 is the Image of the Object in the top mirror using equal perpendicular distances .

Image 5 can also be used as the Object to find Image 3 in the image of the top mirror (Image 2)

4) Show the location of all images in the mirrors which intersect at 60°.

Find the first image (Image 1) in the bottom mirror using equal perpendicular distances .

The top mirror forms an image (Image A) in the bottom mirror.

Use Image 1 as the object to find Image 2.

The bottom mirror forms an image in the image of the top mirror (Image A).

Image 3 is the image of Image 2 in the image mirror.

Image 4 is the image of the object in the top mirror.

The bottom mirror forms an image (Image B) in the top mirror.

Image 5 is the image of Image 4 in the Image B mirror.

The top mirror forms an image in the Image B mirror.

5) Show the location of all images in the mirrors which intersect at 45°.

The visual pattern of all images in the mirrors is much easier to remember than the detailed explanations.

6) Show the location of all images in mirrors which intersect at 30°.

The visual pattern of all images in the mirrors is much easier to remember than the detailed explanations.

7) State a rule that predicts the number of images and the angle between the mirrors.

Angle () Between the Mirrors

Number of Images (n)

90 3

60 5

45 7

30 11

n =

7) State a rule that predicts the number of images and the angle between the mirrors.

Angle () Between the Mirrors

Number of Images (n)

90 3

60 5

45 7

30 11

€

n = 360

−1

8) How many images would be formed in the mirrors arranged at the angles in the table?

Angle () Between the Mirrors

Number of Images (n)

72

40

20

10

8) How many images would be formed in the mirrors arranged at the angles in the table?

Angle () Between the Mirrors

Number of Images (n)

72 4

40 8

20 11

10 35

€

n = 36072

−1

€

n = 36040

−1

€

n = 36020

−1

€

n = 36010

−1

A bird can’t fly on one wing (Scottish or Irish proverb. Exact origins lost to time.)

In science, theory and observation must always balance.

Use Hinged Mirrors to check this out.Or use the Applet described in the notes.

8) Show the location of all images in the parallel mirrors.

8) Show the location of all images in the parallel mirrors.

Place an object between two parallel signal mirrors and observe it through the hole in one of the signal mirrors.

9) How are the images in a common Kaleidoscope arranged?

9) How are the images in a common Kaleidoscope arranged?

If you have some Kaleidoscope mirrors (see “Making Kaleidoscope Mirrors”), check it out.

Place a card with a hole in it (or a slide with coloured filters) in front of the Kaleidoscope. Look through it toward a bright light.

The mirrors can be folded in many different ways other than the traditional equilateral triangle.

Kaleidoscope mirrors are traditionally arranged as equilateral triangles.

10)Two mirrors are joined at a 90°angle. The images are shown. How does light reflect from the object so that the Eye-Brain sees Image 5?

The Eye-Brain sees rays of light which appear to come directly from Image 5 passing through the top mirror.

The light rays cannot pass through the opaque top mirror. They must have originated from the object and reflected off the mirror.

This is similar for Image 1 when the Eye-Brain looks at Image 1.

The Eye-Brain sees rays of light which appear to come directly from Image 1 passing through the bottom mirror.

The light rays cannot pass through the opaque bottom mirror. They must have originated from the object and reflected off the mirror.

How does the light reflect from the object so that the Eye-Brain sees Image 3?

Again, rays of light appear to come straight from Image 3 to the Eye-Brain, passing through Image (4) of the bottom mirror then the top mirror.

Since the rays appear to pass through Image (4) of the bottom mirror , they must have reflected off the real bottom mirror as if they had come from Image 1.

The light rays cannot travel through the opaque bottom mirror. They must have come from the object and reflected off the bottom then top mirrors.