Homework Help: Apparent distance of object in planar mirror

1. Jul 12, 2007

leehom

Tanya is sitting in an optometrist’s chair, facing a mirror that is 2.25 m from her eyes. It the eye chart she is looking at is hanging a wall behind her head, 1.75 m behind her eyes. How far from her eyes does the chart appear to be?

Would the answer be 4 m? (2.25 m +1.75 m)... I'm assuming it's a plane mirror

2. Jul 12, 2007

Chi Meson

Yes, it's this simple.

3. Jul 12, 2007

leehom

Yeah.... can i explain in words, that since it's a plane mirror, etc.

4. Jul 12, 2007

leehom

BTW, is it possible for you to help me with a few other physics (optics) questions??? I'm really really confused..

5. Jul 12, 2007

Kurdt

Staff Emeritus
Would it not be 6.25m?

6. Jul 12, 2007

Kurdt

Staff Emeritus
Feel free to post any physics homework related questions in this forum.

7. Jul 12, 2007

Chi Meson

Whoops, yes it s. I didn't read the question closely.

Leehom: How far is the chart from the mirror?

8. Jul 12, 2007

leehom

I'm sorry I don't understand where the 6.25 m came from... can you pls. explain?

9. Jul 12, 2007

Chi Meson

Read the question and tell me: how far is the chart from the mirror?

10. Jul 12, 2007

leehom

And why would charts used for this purpose have to be specially made?

11. Jul 12, 2007

leehom

I think I get it now... 2.25 m + 2.25 m + 1.75 m = 6.25 m...

12. Jul 12, 2007

Chi Meson

If you don't answer my question, I'm leaving.

Edit:

Phew! Just in time!

13. Jul 12, 2007

Kurdt

Staff Emeritus
Why do you think charts would have to be specially made?

14. Jul 12, 2007

Chi Meson

Is this one of the questions? All optometrist's charts are "specially made."

15. Jul 12, 2007

leehom

well... i wrote that the letters would have to "reversed" so that they would appear upright in the mirror according to prop. of images formed by a plane mirror...

and another quick verification on this question:
Light is shining on to a plane mirror at an angle of incidence of 27 deg. If the plain mirror is tilted such that the angle of incidence is reduce by 8 deg, what will be the total change in the angel of reflection from the original reflected light?

Would the change be 8 deg due to law of reflection? since the angle of reflection is calculated from the normal

16. Jul 12, 2007

Chi Meson

If you tilt the mirror, you tilt the normal. That means both the incident angle and the reflected angle increase by 8 degrees.

17. Jul 12, 2007

leehom

But the question specifically states that the incident angle is reduced by 8 deg