New
New
Year 11
Edexcel
Foundation

Converging lenses

I can use a converging lens to form an image on a screen, and describe how the image can vary depending on the object distance.

New
New
Year 11
Edexcel
Foundation

Converging lenses

I can use a converging lens to form an image on a screen, and describe how the image can vary depending on the object distance.

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Lesson details

Key learning points

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

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.

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.

Make sure to give students a converging lens so they can form a live, full-colour image of the view outside a window. This is so simple but always produces a 'wow' response. It works best on a bright day with the lights dimmed. The practical in task B may work well as a teacher demonstration.
Teacher tip

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
When a wave crosses a boundary and changes direction, this is called .
Correct Answer: refraction, refracting
Q2.
Which diagram shows the ray moving from air into glass and bending in the correct direction?
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz
Q3.
Which diagram shows the ray moving from glass into air and bending in the correct direction?
An image in a quiz
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz
Q4.
In a ray diagram, a normal line is often drawn. Which of the following statements about the normal are correct?
Correct answer: It is an imaginary line.
It is parallel to the boundary.
Correct answer: It is perpendicular to the boundary.
Its length equals the wavelength of the wave.
Correct answer: It passes through the point where the ray hits the boundary.
Q5.
Which of the following statements about the apple shown is correct?
An image in a quiz
Correct answer: 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.
Q6.
Which of the following ray diagrams is correct?
An image in a quiz
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz

6 Questions

Q1.
Images of an object that are smaller than the object's actual size are described as images.
Correct Answer: diminished, reduced
Q2.
What is the name of the point labelled X in the diagram shown?
An image in a quiz
focal length
Correct answer: principal focus
principal axis
Q3.
Which option completes the sentence? An image formed on a screen by a converging lens is always ___________.
magnified
diminished
upright
Correct answer: inverted
Q4.
Which of the following could be correct reasons why this lens cannot produce an image of this object?
An image in a quiz
The lens power is too great.
Correct answer: The object is too close to the lens.
The lens is curved too much.
Correct answer: The focal length is too long.
Q5.
Match each object distance with the correct characteristics of the image. (f = focal length of the lens)
Correct Answer:object distance > 2f,Image located between f and 2f, and is diminished.

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

Correct Answer:object distance = 2f,Image located at 2f, and is life–size.

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

Correct Answer:object distance between 2f and f, Image located further away than 2f, and is magnified.

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

Correct Answer:object distance = f,No image forms as rays leaving the lens are parallel.

No image forms as rays leaving the lens are parallel.

Correct Answer:object distance < f,No image forms as rays leaving the lens are diverging.

No image forms as rays leaving the lens are diverging.

Q6.
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?
An image in a quiz
The lens makes all of the rays meet at a single point.
Correct answer: 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

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