Practical No. 2

[AnnabelleBuda]

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[AnnabelleBuda]

Testing Practical No. 2 (Periscope)

Creating the periscope

A 50 cm long tube of cardboard was created by duct-taping two separate scrap pieces together (Figure 1).

Figure 1: Two pieces of carboard duct-taped together in a tube.

Holes were cut on either side of the tube facing opposite directions to fit the mirrors (Figure 2). The mirrors were inserted at a 45 degree angle to the opening with the reflective sides facing each other. They were held in place using blu-tack on each corner of the mirror and duct-tape over the back. Some adjustment was necessary to correctly position them.

Figure 2: Holes cut into the tube and mirrors inserted and held in place with blu-tack and duct-tape.

The tube was then covered in duct-tape to provide stability and prevent light from entering the tube and obscuring the image provided by the periscope.

Figure 3: Duct-tape was used to cover the whole periscope.

The periscope works well, the image seen in the mirror is clear.
Some issues to consider:

• A lighter, thinner cardboard would be better as box-cutters are unsafe for use by children.
• A neater design would use a template traces out on a large piece of cardboard. This would also be easier for flat-packing in a kit. This would also eliminate the need for duct-taping, which is difficult to handle.

After creating the periscope

• The students can draw images seen through the periscope around corners, over tables etc.
• One student can describe an image and another can draw it.
• The students can diagram how they think the light moves through the periscope to give them the images they see.

Figure 4: Periscope diagram and function.

Activities

• The teacher can set up a display around a corner or on top of a cupboard where the students cannot see and the students can use their periscopes to look at and draw these objects.

[AnnabelleBuda]

Teachers Information Sheet

This practical seeks to address aspects of the Working Scientifically and Physical World sections of the syllabus. In this experiment, students will cover the following dot points:

• classify materials as transparent, opaque or translucent, based on whether light passes through them, is absorbed, reflected or scattered
• gather evidence to support their predictions about how light travels and is reflected
• research, using secondary sources to gather information about science understandings, discoveries and/or inventions that depend on the reflection and refraction of light and how these are used to solve problems that directly affect people's lives, eg mirrors, magnifiers, spectacles and prisms
• predicting what the findings of an investigation might be

Equipment List

Demonstration

• Tennis ball
• Angled surface
• Mirror
• Laser/ torch

Periscope

• Cardboard (milk carton)
• X2 mirrors (approx 5x5 cm)
• Tape
• Duct-tape
• Scissors
• Blu-tack
• Pencils
• Protractor
• Stickers/ paint (for decoration)

Worksheets

• Teacher information sheet
• Student activity questions and instructions

Method

1. Begin by demonstrating that light can be reflected at different angles using the analogy of a ball bouncing off an angled surface.
2. Have students draw diagrams labelling materials and the path of the light. .
3. Have the students build a periscope to demonstrate how reflection can be used redirect light.
4. Have students draw a diagram of what they see through their periscope.

Making a periscope:

1. Create a cardboard prism using the template given.
2. Cut a hole big enough to fit one mirror on one side of the carton
3. Cut a hole big enough to fit one mirror on the other end on the opposite side of the carton.
4. Insert the mirrors so they sit at a 45 degree angle facing each other, with the mirrored side facing the hole. Fix them in place with blu-tack.
5. Look through one end of the periscope. You should be able to see clearly out the other end. If not, re-adjust the mirrors.
6. Pick a spot in the classroom through the periscope and draw what you see using the periscope.

Background Information:

Light is composed of waves, and these waves are the perfect size to allow us to see. It is on a spectrum that includes even longer wavelengths like heat and microwaves and even shorter wavelengths like x-rays that you cannot see. Wavelengths of the right size can be used to ‘see’ different things. For example, radiowaves are very big (in the range of metres) so we can use them to travel across long distances like the signal when you listen to the radio!

Figure 1: Diagram of electromagnetic spectrum from
https://sites.google.com/a/coe.edu/principles-of-structural-chemistry/relationship-between-light-and-matter/electromagnetic-spectrum

These waves can hit materials and bounce off, giving us reflections like what you see in a mirror. This is analogous to a ball hitting a surface and bouncing off. Alternatively, some of the energy from the light can be absorbed by a material, resulting in colours. For example, leaves are green because the pigment absorbs the blue and red wavelengths of light but not the green wavelengths, so we see the green colour. There are other ways light can interact with materials such as scattering, but that is not the focus for this practical.

When light hits a flat surface like a mirror and reflects, it collides with the surface at what is called the angle of incidence. This is the angle between the ray of light and an imaginary line perpendicular to the mirror surface called the ‘normal’ line. The angle at which the light will bounce off the material is simply a reflection of the angle of incidence. This is called the angle of reflection. So, students will learn that when a light ray hits a flat reflective surface, it doesn’t simply bounce straight back into their eyes, the angle it bounces depends on the angle of incidence. By demonstrating this effect first with a physical object like a tennis ball, the students will find it easier to grasp the concept.

The periscope uses angles of incidence and reflection inside the tube to conduct the light to your eyes, thus allowing you to see things over a wall or from an angle where the objects cannot normally be seen.

A mirror, such as those used in the periscope is an opaque material, as the light does not pass from one side to the other (you cannot see through it). Translucent means that some light, but not all passes through, so the image you see through translucent materials is not clear. Transparent means all the light passes through (eg clean glass) so the image you see through the material is clear.

Troubleshooting

• The periscope mirrors may be difficult to line up, and may require some adult help. However, you may choose to ask them why they aren’t seeing what they expected to see in the periscope.
  

[AnnabelleBuda]

Student Inquiry Sheet

1. Label the following materials as translucent, transparent and opaque:

• Wool socks
• Mirror
• Frosted glass windows
• Gum leaf
• Whiteboard

2. The angle between the flat mirror and the normal line is 90 degrees. The angle next to the angle of incidence is 35 degrees. What is the angle of reflection?

3. In a periscope, the light enters the top of the tube and hits the mirror at the top. The light then travels in a line down to the bottom mirror and is reflected out to our eyes. Find the mirror angle and the 2nd angle of reflection in the diagram. Remember the normal line is perpendicular to the mirror.

4. Predict what would happen if the mirrors were not angled correctly in the periscope.

[AnnabelleBuda]

Student Reflection Sheet

1. What did you notice about the images you saw through your telescope? Where they bigger or smaller than they appeared in real life? Why?
2. What do you think would happen to the image you see if you made the periscope longer by 10 cm? 1 m?
3. List 3 things you could do to improve the periscope design (e.g. make the image clearer, make it useful from different angles, make it sturdier etc.).
4. Write a short creative paragraph about the path that Mr Wave takes from the light source to your eye through your periscope.
5. The angle of reflection is on a flat reflective surface is:
   a. Bigger than the angle of incidence
   b. The same as the angle of incidence
   c. Not a thing
   d. The path along the normal line