Jugnix
← Back to the simulation

Jugnix · free physics worksheets

Convex & Concave Lenses Worksheet

Class 10 Science · about 40 minutes · open the simulation at jugnix.com/simulations/lenses

NameClassDate

By the end you will: find the image for every position of the object, use the lens formula and power, and draw ray diagrams.

A. Explore with the simulation

  1. Choose Convex lens with a focal length of 15 cm. Use the “Put the object…” buttons and fill in the table.

    ObjectPosition of imageSize of imageNature of image
    Beyond 2F
    At 2F
    2F–F
    At F
    Inside F

  2. Set the object distance to 30 cm. Write down v and m from the readouts. Check v with the lens formula 1/v − 1/u = 1/f.

  3. Change the focal length to 20 cm. What is the power of the lens? Write the formula you used.

  4. Switch to Concave lens and move the object everywhere. What kind of image do you always get?

B. Calculate (then check in the simulation)

  1. An object is 20 cm in front of a convex lens of focal length 15 cm. Find the image distance, the magnification and the nature of the image.

  2. An object is 30 cm in front of a concave lens of focal length 15 cm. Find v and m.

  3. Where must the object be for a convex lens to work as (a) a camera, (b) a projector, (c) a magnifying glass?

C. Draw it

  1. Draw two rays from the tip of the object, then mark the image. Describe it.

    Blank ray diagram: a convex lens with F₁, 2F₁, F₂ and 2F₂ marked and an object between F₁ and 2F₁, for students to draw the rays and the image.

Answer key (for teachers and parents)

  1. Beyond 2F₁: between F₂ and 2F₂, diminished, real and inverted · At 2F₁: at 2F₂, same size, real and inverted · Between F₁ and 2F₁: beyond 2F₂, enlarged, real and inverted · At F₁: at infinity, highly enlarged, real and inverted · Between F₁ and O: same side as the object, enlarged, virtual and erect.
  2. v = +30 cm, m = −1. Check: 1/v = 1/f + 1/u = 1/15 − 1/30 = 1/30, so v = 30 cm.
  3. P = 100 ÷ f (in cm) = 100 ÷ 20 = +5 D.
  4. Always virtual, erect and diminished, between F₁ and the optical centre, on the same side as the object.
  5. u = −20 cm, f = +15 cm. 1/v = 1/15 − 1/20 = 1/60, so v = +60 cm. m = v ÷ u = 60 ÷ (−20) = −3: real, inverted, three times bigger.
  6. u = −30 cm, f = −15 cm. 1/v = −1/15 − 1/30 = −1/10, so v = −10 cm. m = v ÷ u = (−10) ÷ (−30) = +0.33: virtual, erect, one third the size.
  7. (a) Beyond 2F₁. (b) Between F₁ and 2F₁. (c) Between F₁ and the optical centre O.
  8. A ray parallel to the axis bends through F₂; a ray through O goes straight on. They meet beyond 2F₂, below the axis: a real, inverted, enlarged image. See the solved diagram on the Lenses simulation page.

Free to print and share for teaching. Made with the interactive simulation at jugnix.com/simulations/lenses.