GCSE Physics (AQA)

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Calculating Magnification

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Calculating Magnification

5:54 Types of Image
Spec 4.6.2.5
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  • Magnification of an image can be calculated using the height of the object and the image on a ray diagram.
  • A ray diagram helps determine where and how an image is formed by a lens.
  • A converging convex lens is represented by a specific symbol.
  • The principle axis and focuses are drawn to show where rays parallel to the axis will converge.
  • Light rays from the top of the object refract through the lens and converge at the top of the formed image.
  • Magnification is calculated using the formula: Magnification = Image Height / Object Height.
  • Image and object heights can be measured directly from the diagram.
  • Units for image and object height should be in distance units like centimeters or meters.
  • Magnification is a ratio and has no units.
  • Example problem: Calculate magnification using a ray diagram with a concave lens.
  • Steps to solve the example:
  • 1. Draw a ray through the center of the lens.
  • 2. Draw a ray to the lens and through the virtual focus.
  • 3. Draw the image where the rays converge.
  • 4. Measure the height of the image.
  • 5. Substitute values into the formula to calculate magnification.
  • Example calculation: Object height is 6 cm, image height is 2 cm, magnification = 2/6 = 0.33.
  • In exams, a range of acceptable answers is allowed due to measurement from a drawn diagram.

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