Light and Optics (Grade 10)
A lesson where students use mylar to learn about reflection, and use lasers and fiber to learn about fiber optics.
What You Need
Activity 1: Sight and Reflection
- 1 piece of mylar
Activity 2: Lake and Fiber
- 1 longer piece of PMMA fiber
- 1 laser pointer
Activity 3: Invisible Lines
- 1 short piece of PMMA fiber (roughly 3") - identified
- 1 short piece of fluorocarbon fishing line (roughly 3") - identified
- 1 short piece of monofilament fishing line (roughly 3") - identified
- 1 clear cup of water
- 1 clear cup of vegetable oil
- Small piece of paper towel
Manual:
PowerPoint:
Safety Notes
Ensure you are familiar with Let's Talk Science's precautions with respect to safe delivery of virtual outreach to youth. These precautions can be found in the manual for this activity.
What To Do
Activity 1: Sight and Reflection
Laser on a mirror demo
- Shine a laser/light onto a mirror so it reflects onto a wall.
- Or show a prepared video of this demo.
Activity 2: Lake and Fiber
Testing out the fiber:
- Each student should have one long piece of PMMA fiber and a laser pointer.
- Try pointing the light inside one end of the fiber. It helps if you hold the laser pointer right up at the end of the fiber, so it's shining directly into it.
- Make some observations about how light behaves in the fiber - Where do you see light? Where don't you see light? Why?
Putting a bend in the fiber:
- Point your laser pointer into the fiber again.
- This time, while shining your light through the fiber, try gently bending a section of the fiber. Make some observations.
- Try putting a sharper bend in the fiber. What happens now?
Activity 3: Invisible Lines
Each student should have 1 piece of PMMA fiber, 1 small piece of monofilament fishing line, and 1 small piece of fluorocarbon fishing line, as well as 1 cup of water, 1 cup of vegetable oil and a napkin/paper towel to wipe the pieces on.
- Try putting each of the clear materials into the water and into the oil.
- Write down some observations about each combination. How well can you see the transparent material in the water/oil? Why do you think that is?
Discovery
Activity 1: Sight and Reflection
What's happening when we shine the laser on the mirror? The laser emits light. We can see the light from the laser at the mirror and at the wall because the wall and mirror are illuminated objects, but not in between because there are no objects in between that are illuminated. To see something, we need light to travel to our eyes. When there is nothing in the beam's path, non of the laser light reaches our eyes. However, if you spritz water in the path, water is an illuminated object and allows light to be reflected off it to our eyes, so we can see the pathway of red light where the water droplets are.
When we shine a light into a mirror, the light is reflected and we see an image. There is a law called the law of reflection. This law states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.
Activity 2: Lake and Fiber
Testing out the fiber: What did you observe?
Light was coming out of the other end of the fiber, but we couldn't see the light as it was travelling through the fiber. In the fiber, the light was getting reflected by the fiber every time it got to the edge, at the interface between plastic and air. We can't see it while it is in the fiber because none of the light can escape to reach our eyes.
Putting a bend in the fiber. What do you observe?
For wider, gentle bends, nothing seems to change - the light stays in the fiber. For sharper bends, some of the light starts to escape the fiber and we can see a bit of glowing near the bend. Why do you think this is happening? As we bend the fiber, we are changing the angle of incidence. When the angle of incidence becomes too small, some of the light is transmitted - it is not all reflected inside of the fiber. This is called the bending loss. In situations where we want to keep light trapped, we have to make sure we aren't putting any sharp turns in our fiber or the light will leak out.
Activity 3: Invisible Lines
What did you notice? Did all transparent materials look the same in the water or oil?
The plastic fiber looked almost invisible in the oil but was visible in the water. Fluorocarbon fishing line looked almost invisible in the water.
If the refraction of index "n" is the same, which means the light travels at the same speed, there will be no reflection and no change in the light passing through. The close the index of refraction is between 2 materials, the less light will be affected as it's passing through.
What's Happening?
Activity 1: Sight and Reflection
What's happening when we shine the laser on the mirror? The laser emits light. We can see the light from the laser at the mirror and at the wall because the wall and mirror are illuminated objects, but not in between because there are no objects in between that are illuminated. To see something, we need light to travel to our eyes. When there is nothing in the beam's path, non of the laser light reaches our eyes. However, if you spritz water in the path, water is an illuminated object and allows light to be reflected off it to our eyes, so we can see the pathway of red light where the water droplets are.
When we shine a light into a mirror, the light is reflected and we see an image. There is a law called the law of reflection. This law states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.
Activity 2: Lake and Fiber
Testing out the fiber: What did you observe?
Light was coming out of the other end of the fiber, but we couldn't see the light as it was travelling through the fiber. In the fiber, the light was getting reflected by the fiber every time it got to the edge, at the interface between plastic and air. We can't see it while it is in the fiber because none of the light can escape to reach our eyes.
Putting a bend in the fiber. What do you observe?
For wider, gentle bends, nothing seems to change - the light stays in the fiber. For sharper bends, some of the light starts to escape the fiber and we can see a bit of glowing near the bend. Why do you think this is happening? As we bend the fiber, we are changing the angle of incidence. When the angle of incidence becomes too small, some of the light is transmitted - it is not all reflected inside of the fiber. This is called the bending loss. In situations where we want to keep light trapped, we have to make sure we aren't putting any sharp turns in our fiber or the light will leak out.
Activity 3: Invisible Lines
What did you notice? Did all transparent materials look the same in the water or oil?
The plastic fiber looked almost invisible in the oil but was visible in the water. Fluorocarbon fishing line looked almost invisible in the water.
If the refraction of index "n" is the same, which means the light travels at the same speed, there will be no reflection and no change in the light passing through. The close the index of refraction is between 2 materials, the less light will be affected as it's passing through.