Scale diagrams for convex lenses (including magnification) | Starter Quiz | Oak National Academy

A lens that bends light rays towards each other so that they meet or cross is called a ___ lens.

Answer explanation

A convex lens bulges outwards so that it is wider in the middle. It makes light rays converge (come together).

A student wants to use a lens to create an image on a screen. At which position should the student place the screen to see a sharp image?

• Position A

• Position B

• Position C

• Position D

Answer explanation

For the image to be sharp (clear and not blurry), rays from one point on the object must arrive at the same place on the screen.

A student uses a lens to create an image of a car. The real car is 400 cm long. The image of the car is 8 cm long. What is the magnification of the image?

• -50

• 0.02

• 50

• 392

• 3200

Answer explanation

Magnification = image height ÷ actual height = 8 ÷ 400 = 0.02. Although the image is smaller than the object, this can still be described as a magnification.

Which of these words can be used to describe images made on screens by lenses?

• diminished

• inverted

• life-sized

• magnified

• upright

Answer explanation

Compared with the object, the image is: larger if the object is further than 2f (twice the focal length) from the lens; the same size if the object is exactly 2f from the lens; smaller if the object is closer than 2f but farther than f from the lens.

The diagrams show parallel light rays being brought to a focus by three different lenses, labelled P, Q and R. Lenses P and Q have the same curvature. Which of these statements must be true?

• Lens P refracts rays through the largest angles.

• Lens P and lens Q are made of different materials.

• Lens R has the highest power.

• Lens R has the shortest focal length.

Answer explanation

The lenses in order of increasing power are P, Q, R. Lens R refracts (bends) rays through the greatest angles, bringing them to a focus nearest the lens. Lenses P and R have the same shape but different powers, so must be made of different materials.

A student uses a lens to make a sharp (clear) image of an object on a screen. Which of these statements must be correct?

• The light rays hitting the lens are parallel or very nearly parallel.

• By moving the screen, the student can see sharp images of different sizes.

• The lens brings all rays from one point on the object to one point on the image.

• The distance between the lens and the image equals the focal length of the lens.

Answer explanation

The lens refracts parallel rays towards each other so that the rays become converging. It can do this to diverging rays as well as to parallel rays. The more diverging the rays are, the farther the focused image will be from the lens.