AnnabelleBuda
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6 years ago 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
- Begin by demonstrating that light can be reflected at different angles using the analogy of a ball bouncing off an angled surface.
- Have students draw diagrams labelling materials and the path of the light. .
- Have the students build a periscope to demonstrate how reflection can be used redirect light.
- Have students draw a diagram of what they see through their periscope.
Making a periscope:
- Create a cardboard prism using the template given.
- Cut a hole big enough to fit one mirror on one side of the carton
- Cut a hole big enough to fit one mirror on the other end on the opposite side of the carton.
- 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.
- Look through one end of the periscope. You should be able to see clearly out the other end. If not, re-adjust the mirrors.
- 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.
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).
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.
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.
The periscope works well, the image seen in the mirror is clear.
Some issues to consider:
After creating the periscope
Activities