# Optics - For what distance must we focus our eyes to see this image

An object is placed 1m in front of a plane mirror. An observer stands 3m behind the object. For what distance must the observer focus his eyes in order to see the image of the object?

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Mentallic
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5 metres? Was that all there is to the question?

Yeah that is all the question was. How did you figure that out?

tiny-tim
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An object is placed 1m in front of a plane mirror. An observer stands 3m behind the object. For what distance must the observer focus his eyes in order to see the image of the object?
Hi Kathi!

Hint: for a plane mirror, where is the image in relation to the object?

Do you mean that it is in an angle? I am not quite sure of the answer you are looking for

tiny-tim
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Do you mean that it is in an angle? I am not quite sure of the answer you are looking for
Mirrors are like lenses … every object has an image.

For a plane mirror, where is the image of an object?

The image is located in front of the mirror. Isn't the image distance equal to the object distance. Thus it would be 3m

Ok so now that I am thinking about, is the image behind the mirror or in front. I am starting to think it is behind?

tiny-tim
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Ok so now that I am thinking about, is the image behind the mirror or in front. I am starting to think it is behind?
Yup, the image is definitely behind the mirror!

(It's a virtual image: the rays of light "from" it don't actually get anywhere near it, do they? )

Sooo … how far away from the observer is the image of that object she's standing behind?​

The object is 1m away and the person is 3m away so it would be 3m +1m + the 1m behind the mirror so it would be 5m.

tiny-tim