# Physics P3 1.5 Lenses.

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What does a converging lens do?
Focuses parallel rays to a point called the principal focus.
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What does a diverging lens do?
Makes parallel rays spread out as if they came from a point called the principal focus.
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When is a real image formed b a converging lens?
If the object is further away than the principal focus.
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When is a virtual image formed by a converging lens?
If the object is nearer to the lens than the principal focus.
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What are the images formed by a diverging (concave) lens?
They are always virtual.
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How can magnification be calculated?
Using the equation: magnification = image height over object height (look up).
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What happens to parallel rays of light that pass through a converging (convex) lens?
They are refracted so that they converge to a point.
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What is the point at which refracted parallel rays of light that pass through a converging (convex) lens converge called?
The principal focus (focal point).
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What is the distance from the centre of the converging (convex) lens to the principal focus called?
The focal length.
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Why is there a principal focus on either side of the converging (convex) lens?
Because light can pass through the lens in either direction.
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What happens if the object is further away from a converging (convex) lens than the principal focus?
An inverted, real image is formed.
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What does the size of the the image viewed through a converging lens depend on?
The position of the object, the nearer the object is to the lens, the larger the image.
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If the object is nearer to the converging (convex) lens than the principal focus, what image is formed?
An upright , virtual image is formed behind the object. The image is magnified - the lens acts as a magnifying glass.
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What happens to parallel rays of light that pass through a diverging (concave) lens?
They are refracted so that they diverge away from a point, this point is called the principal focus.
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What is the distance from the centre of a diverging (concave) lens to the principal focus?
The focal length.
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How is there a principal focus on either side of a diverging (concave) lens?
Because light can pass through the lens in either direction.
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What s the principal focus of a converging (convex) lens?
The point where rays of light parallel to the principal exist are brought to a focus.
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How can a converging lens be made to produce a virtual image?
By placing an object between the lens and the principal focus.
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**LOOK UP THE SYBOLS THAT CAN BE USED IN RAY DIAGRAMS TO REPRESENT LENSES**
**MAKE SURE YOU DON'T CONFUSE THE TERMS 'CONVERGING' AND 'DIVERGING'**
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**LOOK UP A DIAGRAM OF THE FOCAL LENGTH OF A CONVERGING LENS AND A DIVERGING LENS**
**
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## Other cards in this set

### Card 2

#### Front

What does a diverging lens do?

#### Back

Makes parallel rays spread out as if they came from a point called the principal focus.

### Card 3

#### Front

When is a real image formed b a converging lens?

### Card 4

#### Front

When is a virtual image formed by a converging lens?

### Card 5

#### Front

What are the images formed by a diverging (concave) lens?