Can someone please help me with this physics chart? I'm kind of confused on how to do it.

Question

savannah_noelle · Answer

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matt101 · Answer

Check out these charts to help you understand. Think of where the object is in relation to the focal point that's given (compare the object distance to the focal point). All you need to do is check off what best describes the image in each case! http://en.wikipedia.org/wiki/Curved_mirror#Image http://en.wikipedia.org/wiki/Curved_mirror#Image_2

savannah_noelle · Answer

@matt101 thank you! But do you know how to solve it?

matt101 · Answer

I'll walk you through the first one. In general, for concave mirrors, there are a few rules that are good to know when you're drawing your light rays and trying to figure out where your image is:

1) A light ray from the object traveling PARALLEL to the normal will be reflected by the mirror through the FOCAL POINT.

2) A light ray from the object traveling through the FOCAL POINT will be reflected by the mirror PARALLEL to the normal.

3) A light ray traveling through the CENTRE OF CURVATURE will be reflected BACK through the centre of curvature.

The wikipedia page I linked have all light rays drawn according to these rules. Now, keep in mind the image is at the location where the reflected rays intersect.

For your first trial, they say the object is 30 cm from the mirror. This means the object is not only past the focal point (10 cm), but it's also past the centre of curvature (double the focal distance, 20 cm). If you draw you light rays according to the rules above, you'll find they intersect to form an image with these characteristics:

- The image distance is given by the mirror equation, 1/d(o) + 1/d(i) = 1/f. If you plug in the object distance, d(o), and the focal distance, you find that the image distance, d(i), is 15 cm away from the mirror

- You'll also see from your drawing that the size of the image is smaller than your object

- You'll also see from your drawing that the orientation of the image is inverted (upside-down) compared to your object

- Finally, you'll notice from your drawing that the image is located on the same side of the mirror as your object, meaning it is a real image

Now try to follow this process for the other trials. Hope this helps!

savannah_noelle · Answer

Thank you so much!

savannah_noelle · Answer

@matt101 would I use this equation for every trial?

matt101 · Answer

Yes - just keep in mind the focal point is negative (i.e. BEHIND the mirror) for convex mirrors.