Physics·Properties of waves · NSSCO 4.2.1
The basic concepts of light
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Light is something you use every second of the day, yet it obeys one beautifully simple rule: it travels in straight lines. From that single idea we can explain rays and beams, luminous and non-luminous objects, how we see, how shadows form with their umbra and penumbra, eclipses of the Sun and Moon, the clever pinhole camera, and the astonishing speed of light.
What you'll learn in this lesson
By the end you should be able to (NSSCO Physics 4.2.1):
- Explain that light is a form of energy that travels in straight lines (rectilinear propagation)
- Describe a ray and a beam, and the three types of beam (parallel, divergent, convergent)
- Outline the difference between luminous and illuminated (non-luminous) objects, and explain how we see
- Explain how the straight-line travel of light leads to the formation of shadows, including the umbra and penumbra
- Explain eclipses of the Sun and Moon, including the terms umbra and penumbra
- Explain the formation of the image in a pinhole camera and why it is inverted
- State that light travels extremely fast (c = 3 × 10⁸ m/s in a vacuum)
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