Difference between revisions of "Convex Lens"
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: A '''convex lens''' causes [[parallel]] [[Light Ray|rays]] of [[light]] to [[converge]], so it can also be called a [[Converging Lens|converging lens]]. | : A '''convex lens''' causes [[parallel]] [[Light Ray|rays]] of [[light]] to [[converge]], so it can also be called a [[Converging Lens|converging lens]]. | ||
: A '''convex''' [[lens]] is used to [[focus]] [[light]]. | : A '''convex''' [[lens]] is used to [[focus]] [[light]]. | ||
| + | : Projecting an [[image]] onto a [[screen]] using a '''convex [[lens]]''' creates a [[Real Image|real image]]. Looking through a '''convex [[lens]]''' the [[image]] seen is a [[Virtual Image|virtual image]]. | ||
===Finding the Focal Length=== | ===Finding the Focal Length=== | ||
Revision as of 12:37, 24 February 2019
Contents
Key Stage 3
Meaning
A convex lens is a shaped piece of glass that is thickest at the centre and thinnest at the edges.
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| A picture of a convex lens. | The symbol used in diagrams to represent a convex lens |
About Convex Lenses
- A convex lens causes parallel rays of light to converge, so it can also be called a converging lens.
- A convex lens is used to focus light.
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| A convex lens focuses parallel rays to a focal point. |
Key Stage 4 Higher
Meaning
A convex lens is a shaped piece of glass that is thickest at the centre and thinnest at the edges.
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| A picture of a convex lens. | The symbol used in diagrams to represent a convex lens |
About Convex Lenses
- A convex lens causes parallel rays of light to converge, so it can also be called a converging lens.
- A convex lens is used to focus light.
- Projecting an image onto a screen using a convex lens creates a real image. Looking through a convex lens the image seen is a virtual image.
Finding the Focal Length
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| A convex lens focuses parallel rays to a focal point. |
- The focal length of a convex lens is the distance between the focal point and the centre of the lens.
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| A diagram showing how to find the focal length of a convex lens. |
To find the Focal Length of a convex lens:
- Focus the image of a "distant object" onto a screen.
- Measure the distance between the lens and the screen.
- The image distance (the distance between the focussed image and the lens) is the same as the focal length for a "distant object".
- If the object distance (the distance between an object and a lens) is too small, then the focal length is not the same as the image distance.
Ray Diagrams
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| A ray diagram for a convex lens.
In this diagram: "Ray 1" is shown crossing the focal point of the lens after being refracted. "Ray 2" is shown passing through the centre of the lens. "Ray 3" is shown crossing the focal point before the lens. The diagram shows that a diminished real image is produced when the object distance is greater than the focal length of the convex lens. |
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| Comparing these two diagrams shows that the image size increases as the object distance approaches the focal length of the lens. | |
Magnification
For further details, see magnification.
The equation for the magnification of a convex lens is:
Magnification = (Image Length)/(Object Length)
\(Magnification = \frac{L_i}{L_o}\)
Where\[{L_i}\] = Length of the image.
\({L_o}\) = Length of the object.