An object is 10 cm from the mirror, its height is 1 cm and the focal length is 5 cm. What is the distance from the image to the mirror?

Question

roadjester · Answer

$$\frac 1 f=\frac 1 p+\frac 1 q$$

anonymous · Answer

What do p and q stand for?

roadjester · Answer

It's the mirror equation.

roadjester · Answer

Actually, that won't help in this particular problem since what you were given was a ratio.

roadjester · Answer

$\LARGE \dfrac {h'}{h}= \dfrac {q}{p}$

roadjester · Answer

Let me just draw an image to go with that.

anonymous · Answer

I believe that formula is the one I was trying to use, although the one in my book is a little different. $$\frac{H _{o} }{ H _{i}} = \frac{ S _{o} }{ -S {i} }$$

roadjester · Answer

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roadjester · Answer

hmm, most likely; the symbols in different books will be different

anonymous · Answer

Yeah that's what I was assuming. I just couldn't find all the components, I was only able to determine that Ho = 1cm and So = 10cm

roadjester · Answer

You seem like you know what you're doing. so where are you having trouble?

roadjester · Answer

don't forget you are also given the focal length

anonymous · Answer

Yeah I just realized I may be able to use that with the first equation. I do mostly know what I'm doing, I just get stuck on little stuff.

roadjester · Answer

Ok so the first equation i wrote, f is focal length
p is the distance from the mirror, and q is the reflection's distance from the mirror

roadjester · Answer

so what you need to do first is find q

roadjester · Answer

after you find q, you can then use that ratio

roadjester · Answer

make enough sense?

anonymous · Answer

Yeah I have the equation $$\frac{ 1 }{ f } = \frac{ 1 }{ So } + \frac{ 1 }{ si }$$
And Si is what I need.

anonymous · Answer

I think I've got it, thanks for your help.

roadjester · Answer

just make sure that the signs are correct and to check your units

roadjester · Answer

some books are evil and give you a height in cm and a length in m or something
and you're like "what did I do wrong???"

roadjester · Answer

=)

anonymous · Answer

Ughh I know, thankfully everything was in cm here.

roadjester · Answer

cool. good luck!

roadjester · Answer

Optics is usually easier in E&M

roadjester · Answer

Until you get to interference and diffraction anyways.