Unit C: Light and Optical Systems

Key Ideas     Unit Checklist

Pre-assessment: What do you know?


Figure C.P.1 – Nuclear reactions in the sun produce light energy.

Figure C.P.2 – Burning fuel produces light.


Figure C.P.3 – Electricity produces bright lights in our modern world.
Light is an energy form that living things need to survive on Earth. Photosynthesizing organisms like plants use light energy to make their own food. Higher up on food chains, living things eat photosynthesizing organisms to stay alive.

Light enables us to see. The human eye is a complex structure that detects light and images. Different animals have different eye structures that are specially adapted to help them survive.

Light travels from one place to another. Light’s movement changes when it interacts with different substances. Humans have taken advantage of light’s unique characteristics to build many useful technologies in areas such as communications and medicine.

What is light and how does it behave? How does light enable animals to see?

To learn more about how humans can create new technologies with light, we must understand the properties of light and how we can apply this knowledge to useful tasks.


Figure C.P.4 – Modern communication technologies depend on light.

Figure C.P.5 – Light energy meets many human needs.

Pre-assessment Questions & Hints

Step 1: The Questions


This short pre-assessment is to find out what you might already know about the topic of light and optics. Below are four questions. Think about them! If you need a hint, click on the question.

Optional: If you would like a place to write your answers, download this document .
Think about how light interacts with the human eye.
Think about what happens when light travels through eyeglass lenses.
Think about objects you use everyday that involve light.

Step 2: The Answers

 Click each of the suggested answers below – how do they compare to your thoughts and answers?
Light travels through the air and other objects in straight lines. Light bends when it travels from the air into a different substance. Light does not travel through some objects, but reflects off their surfaces.
Light travels into the human eye. The eye’s lens focuses light into an image at the back of the eye. Receptors at the back of the eye send messages about the image to the brain.
Eyeglasses contain curved glass lenses. The lenses in eyeglasses bend, or refract light, to form a clear image in the eye.
Many modern technologies rely on light. One example of a technology that relies on light is fiber optic cables that carry telephone and internet signals. Another technology that uses light is microscopes that magnify tiny organisms.

Step 3: Check In With Your Teacher

The start of a new unit is a great time to touch base with your teacher! Here are just a few reasons to consider contacting your teacher:

  1. Perhaps you found this pre-assessment quiz very easy because you have studied this material before, such as at another school. If so, it's important to tell your teacher.

  2. It's very good for your teacher to know you are starting a new unit; it will give them a good idea of your progress. It doesn't have to be a long message, just a "I'm starting Unit C; just thought you might want to know!"

  3. Your teacher may have special tips and suggestions for the unit you are starting.

  4. Just to say hi – your teacher always enjoys hearing from you!

To contact your teacher, post in the Course Questions Forum, send your teacher an email, or call on the phone if you like. Whatever way you choose, it's always a good idea to get in touch with your teacher – make sure you do it frequently.