Converging lenses | Physics | Quizalize & Oak National Academy

Starter quiz

When a wave crosses a boundary and changes direction, this is called ______.

'refraction' ✓
Which diagram shows the ray moving from air into glass and bending in the correct direction?
Which diagram shows the ray moving from glass into air and bending in the correct direction?
In a ray diagram, a normal line is often drawn. Which of the following statements about the normal are correct?

It is an imaginary line. ✓

It is parallel to the boundary.

It is perpendicular to the boundary. ✓

Its length equals the wavelength of the wave.

It passes through the point where the ray hits the boundary. ✓
Which of the following statements about the apple shown is correct?

The apple reflects light. ✓

The apple refracts light.

Light coming from a point on the apple always travels in a single direction.

Light travelling from the apple in one direction all comes from one point.
Which of the following ray diagrams is correct?

Exit quiz

Images of an object that are smaller than the object's actual size are described as ______ images.

'diminished' ✓
What is the name of the point labelled X in the diagram shown?

focal length

principal focus ✓

principal axis
Which option completes the sentence? An image formed on a screen by a converging lens is always ___________.

magnified

diminished

upright

inverted ✓
Which of the following could be correct reasons why this lens cannot produce an image of this object?

The lens power is too great.

The object is too close to the lens. ✓

The lens is curved too much.

The focal length is too long. ✓
Match each object distance with the correct characteristics of the image. (f = focal length of the lens)

object distance > 2f

⇔

Image located between f and 2f, and is diminished. ✓

object distance = 2f

⇔

Image located at 2f, and is life–size. ✓

object distance between 2f and f

⇔

Image located further away than 2f, and is magnified. ✓

object distance = f

⇔

No image forms as rays leaving the lens are parallel. ✓

object distance < f

⇔

No image forms as rays leaving the lens are diverging. ✓
The diagram shows many rays of light travelling from 4 points on an object passing through a lens. Given that object distance > focal length, which of the following statements are correct?

The lens makes all of the rays meet at a single point.

All the rays from a single point on the object meet at a single point. ✓

The image will appear at the focal length of the lens.

At this object distance, an image of the tree cannot be formed on a scree

Worksheet

Loading worksheet ...

Presentation

Loading presentation ...

Video

Lesson Details

Key learning points

Converging lenses can produce an inverted image on a screen by refracting light.
Rays parallel to the principal axis are refracted to the principal focus of a converging lens (at the focal length).
The image distance and size (magnification) depend on the power of the lens and the object distance.
As the object distance decreases, the image distance and size both increase, until the object reaches the focal length.
If the object is too close to the lens, the rays leaving the lens are parallel/diverging, images can't form on a screen.

Common misconception

Pupils often think there is only one ray of light for each point of light on the image.

Many rays of light pass through the lens from each point on the object, but all the rays from a single point arrive at a single point at the image distance. The rays from each point on the object arrive at corresponding points at the same distance.

Keywords

Diminished - Diminished means smaller than an object’s real size. It is the opposite of magnified.
Converging - Light rays are converging if they are coming together to a point where they will meet.
Principal focus - Rays of light incident on a converging lens parallel to the principal axis are focused to a point called the principal focus.
Focal length - The focal length is the distance from the centre of the lens to the principal focus.
Lens power - The greater the power of a lens, the greater the angles through which light is refracted and the shorter the focal length.