# Homework Help: 2 Plane mirror problems. no numbers

1. Apr 8, 2009

### phillyj

1. The problem statement, all variables and given/known data

#1) How many images can be seen? 2 mirrors, one on x axis, other y axis.

2. Relevant equations

Law of reflection: $$\vartheta$$i=$$\vartheta$$r

Is the positioning correct? I thought that rays bounce off the x axis mirror then y axis mirror to give 2 images. The third image came from bouncing off the y axis mirror only. The teacher wanted us to work it out and told us that the answer is 3 but we had to find the position.
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1. The problem statement, all variables and given/known data
#2) Whats the minimum length(h) of a mirror that is needed for a person of height(H) to see his entire reflection? Answer: h=H/2

2. Relevant equations

|m|= |H/h| <= magnification equation needed?

3. The attempt at a solution
I'm not sure how to start. Professor said that the distance between the person and mirror doesn't matter. Someone point me in right direction
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Apr 8, 2009

### rl.bhat

1) Position of image 2 in not correct. Its distance from the axis should be equal to the remaining two images.
2) Draw ray diagram, one from eye and other from foot. Note down the portion of mirror to see the full image.

3. Apr 8, 2009

### phillyj

1) Ok, but my reasoning is correct?
2) I'm not sure how to draw from eye.

4. Apr 8, 2009

### rl.bhat

1) Yes.
2) Draw the ray from head to eye.

5. Apr 8, 2009

### phillyj

2) from top of the head to the eye? the angle of reflection would be very very small? I still can't get this part

6. Apr 8, 2009

### rl.bhat

When you want to your full image, you must see your head and toe. If you want you can take a normal ray from your eye. After reflection it returns back to your eye.

7. Apr 8, 2009

### phillyj

for plane mirrors, isn't the virtual image equal size to the actual image? Magnification=+1

So why is the height of the mirror H/2?

8. Apr 8, 2009

### rl.bhat

Size of the image does not depend on the size of the mirror. Even in a small mirror you can see your full face.

9. Apr 8, 2009

### phillyj

ok, but when I try drawing it, my virtual image is the same size as the actual. Was the partial drawing that I made above correct? I still can't understand how to draw ray from top of head to the eye.

You know of any websites that could help?