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Posted by on Monday, April 7, 2008 at 8:16pm.

1)A 5.0 cm real object is placed at a distance of 30.0 cm from a concave mirror of focal length 10.0 cm. Find the location of the image.

(30)(10)/5.0
15

or (30)(5.0)/10
60

I don't know which one

2)What must be the minimum height of a plane mirror so that a boy of height 162 cm can view himself from head to toe?

162 cm

3)A 5.0 cm real object is placed at a distance of 5.0 cm from a concave mirror of focal length 10 cm. Find the size of the image.

20 cm

  • physics - , Monday, April 7, 2008 at 8:28pm

    3)(10)(5.0)/5.0-10
    answer: 10 cm (I get -10 from the math but that's not one of the choices)

  • physics - , Monday, April 7, 2008 at 8:31pm

    3) I skipped a step but 10 is still the answer.

  • physics - , Monday, April 7, 2008 at 8:32pm

    1) Start with the lens or mirror equation:

    1/do + 1/di = 1/f = 1/10
    1/30 + 1/di = 1/10
    1/di = 2/30
    One of your answers is correct, but you used the wrong formula to get it.

    di = 15 cm is the distance to the image. It makes no difference what the object height is.

    2) wrong

    3) wrong. You are just taking wild guesses. That won't do.

    1/5 + 1/di = 1/10
    1/di = 1/10 - 2/10 = -1/10
    di = -10
    Magnification = |di/do| = ?
    Image size = (object size) * (magnification)= ?

  • physics-it may look like it but im not - , Monday, April 7, 2008 at 8:38pm

    it may look like it but im not

  • physics - , Monday, April 7, 2008 at 8:46pm

    So I was right originally on 3, with 20 cm. For 2, 162/2 = 81 cm

  • physics - , Monday, April 7, 2008 at 10:29pm

    mag = di/do
    mag = -10/5.0
    mag = 2

    im size = o-size * mag
    im size = 5.0 * 2
    im size = 10

  • physics - , Tuesday, August 23, 2016 at 10:15pm

    15

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