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Year 11 - Science

Virtual images from convex and concave lenses (including magnification)

Electromagnetic waves

Unit Summary

This unit explores reflection, refraction, and lenses using ray diagrams. It covers the electromagnetic spectrum, light as a wave, absorption, transmission, and practical uses. Emphasis is on risks, temperature balance, data presentation, and unit conversions.

Lesson Summary

You will learn to describe the formation of virtual images by convex and concave lenses and draw ray diagrams to find the position and magnification of the image.

Key Notes

  • When rays of light are brought to a focus a real image forms. A real image can be projected onto a screen.
  • Virtual images occur at points where rays appear to (but do not actually) originate from. They cannot form on a screen.
  • The size and position of a virtual image is found by drawing virtual rays to find where rays appear to originate from.
  • Upright virtual images are produced by concave lenses, and objects within a focal length of a convex lens.
  • Convex lenses fix long sight by shortening the focus. Concave lenses fix short sight by lengthening the focus.

Vocabulary To Learn

  • principal axis: The principal axis is a line through the centre of a lens, 90° to the optical axis of the lens.
  • principal focus: The principal focus for a convex lens is the point to which rays parallel to the principal axis are focused. For a concave lens it is the point from which such rays appear to be diverged.
  • real image: When rays of light are brought to a focus a real image forms. A real image can be projected onto a screen.
  • virtual image: Virtual images occur at points where rays appear to (but do not actually) originate from. They cannot form on a screen.
  • virtual ray: Virtual rays are dashed lines drawn to represent where rays of light appear to have come from.

Common Mistakes To Avoid

  • Real images always or only form on screens, or a screen is necessary to observe a real image.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key points.

When rays of light are brought to a focus a real image forms. A real image can be projected onto a screen. Virtual images occur at points where rays appear to (but do not actually) originate from. They cannot form on a screen.

2. Define this scientific word and use it in context. 'principal axis'

The principal axis is a line through the centre of a lens, 90° to the optical axis of the lens. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Real images always or only form on screens, or a screen is necessary to observe a real image. Correction: Be clear that real images can form on screens, but can also be observed without a screen. Demonstrate looking through a convex lens (e.g. a magnifying glass) at a diminished, inverted real image of a a distant object.

More Lessons In This Unit

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