An object 5 cm in size is placed at a distance of 20 cm from the concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed to get a sharp image? Also find the height of the image.
Answers
Answer:
Since the mag is 2 X, the height of the image (its size) is: 5 x 2 = 10 cm
Explanation:
There is no single statement that he writes that is a truth. I suggest you ignore his solution. The only item in his solution that is correct is the green ray that is incident on the pole of the mirror. Such rays reflect off the mirror following the first law of reflection. His ray seems to be doing that.
Here is a proper solution to the problem:
We are given R = 20 cm. Then f = R/2 = 10 cm.
Use the mirror formula: 1/10 = 1/15 + 1/Di → Di = 30 cm.
The image distance being positive means that it is REAL. Real images are INVERTED.
The magnification is (30 / 15 = 2 x). The image is MAGNIFIED, and located on the same side as the object.
Since the mag is 2 X, the height of the image (its size) is: 5 x 2 = 10 cm