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Year 8

Focusing light

I can explain how light from an object can be focused by a converging lens to form an image.

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New
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Year 8

Focusing light

I can explain how light from an object can be focused by a converging lens to form an image.

Download all resources
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Share activities with pupils
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Lesson details

Key learning points

  1. Some of the light from objects can pass through a lens and become focused to form an image on a screen.
  2. Some light from every point on an object passes through every part of a lens.
  3. A convex lens refracts light rays so they travel more towards each other. A point where rays meet is called a focus.
  4. All the rays from one point on the object are focused to the same point, forming the corresponding part of the image.
  5. The shape of a converging lens refracts (bends) light more at the edges than near to the centre.

Keywords

  • Lens - a piece of glass or other transparent material shaped to refract light towards or away from a focus

  • Image - a representation of an object

  • Focus - (1) a point where many rays of light from an object meet (2) the process of refracting light rays so they meet

  • Refraction - when light changes direction when it enters a new medium

  • Focal length - the distance from the centre of a lens to where the lens focuses a distant object

Common misconception

Each point of light on an image comes from just one ray of light from a corresponding point on an object.

Show how multiple rays of light from each point of an object pass through a lens and are focused at a single point in the image. Show how covering half of a lens does not cause half of the image to disappear.

Turning lights off and closing one or two blinds is usually sufficient to allow convex lenses to be used to form images of the view from a window on a piece of white paper attached to the opposite wall. The images will be moving and in full colour, inverted and smaller than the object (diminished).
Teacher tip

Equipment

convex lenses (magnifying glasses will do), plain A4 paper

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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Starter quiz

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6 Questions

Q1.
The diagram shows light changing direction as it passes from one medium to another. This effect is called .
An image in a quiz
Correct Answer: refraction, refracting
Q2.
Which of the following statements are correct?
Correct answer: Each point on a luminous object emits light in all directions.
Each point on a luminous object emits light in one direction.
Correct answer: Each point on a non-luminous object reflects light in all directions.
Each point on a non-luminous object reflects light in one direction.
Q3.
A pupil holds up a screen to face the full Moon at night. Which of the following explains why an image of the Moon does not appear on the screen?
No light from the Moon hits the screen.
The light rays hitting the screen are virtual.
Correct answer: Light from every part of the Moon hits every part of the screen.
Each point on the screen is hit by light from only one point on the Moon.
Q4.
A light ray passes from air into a glass block, but it is not refracted. Which of the following statements can explain this?
Transmission and refraction cannot happen together.
Correct answer: The ray meets the glass along the normal to the block’s surface.
The ray meets the glass at 90° to the normal to the block’s surface.
Refraction does not happen when light passes from air into a solid.
Q5.
Light crosses a boundary from one material into another. Which of the following statements is correct?
Correct answer: The greater the angle between a ray and the normal, the more it is refracted.
The smaller the angle between a ray and the normal, the more it is refracted.
The angle between a ray and the normal doesn't affect how much it is refracted.
Q6.
Which of the following diagrams correctly shows light refracting through a rectangular block?
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

Exit quiz

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6 Questions

Q1.
Which of the following statements about images made on a screen by a convex (converging) lens is correct?
A larger lens produces a larger image.
The image can be rotated by turning the lens.
The image is always the same size as the object.
Correct answer: The image is always inverted compared with the object.
Q2.
A pupil wants to use a lens to make an image of a bright object appear on a screen. Where should the pupil put the screen to see a clear image?
at the focal distance from the lens
closer to the lens than the focal distance
further from the lens than the focal distance
Correct answer: It depends on the distance between the lens and the object.
Q3.
The more powerful a lens is, the shorter its focal length. Which of the following changes would make a lens more powerful?
Correct answer: making the lens wider (more curved)
making the lens thinner (less curved)
making the lens from a material that refracts light less
Correct answer: making the lens from a material that refracts light more
Q4.
The diagram shows a lens focusing light from a tree. Three of the rays are shown. At which of the labelled distances is an image formed?
An image in a quiz
A
B
C
Correct answer: D
E
Q5.
Which of the following happen when a lens forms an image of an object?
All rays from one point on the object pass through the same part of the lens.
Correct answer: All rays from one point on the object arrive at the same point in the image.
Correct answer: Rays from all points on the object pass through each part of the lens.
Rays from all points on the object arrive at the same point in the image.
Q6.
The image shows a convex lens. Which of the following statements about the lens is correct?
An image in a quiz
All parts of the lens refract light equally.
The thickest part of the lens refracts light most strongly.
Correct answer: The thinnest parts of the lens refract light most strongly.

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