Real Images (Cambridge (CIE) IGCSE Physics) : Revision Note

Draw a ray diagram to show how a converging lens can be used to form a diminished image of a real object.

Label the object, image and principal foci of the lens on your diagram.

Answer:

Step 1: Start by drawing and labelling a principal axis and the lens as a line or a very thin ellipse

Step 2: Mark and label the focal points on each side of the lens

Step 3: Draw and label the object at a distance greater than the focal length on the left side of the lens

• Tip: For a diminished image the object should be placed a distance of at least 2F away from the lens

Step 4: Draw a ray through the optical centre of the lens 

Step 5: Draw a second ray from the object to the lens which is parallel to the principal axis

Step 6: Draw the continuation of the ray passing through the focal point on the right side of the lens

Step 7: Draw and label the image at the point where the rays meet

Step 8: Check your final image and make sure everything is included to gain the marks

• For a three-mark question, examiners will be looking for:

  • One ray drawn through the optical centre of the lens

  • A second ray drawn which produces a diminished (smaller) image (which must pass through a labelled focal point)

  • Both the object and the image must be drawn and labelled correctly