a) For an image that is in front of a mirror, is the image distance positive or

Question

a) For an image that is in front of a mirror, is the image distance positive or negative?

b) Given the image distance, what additional information is needed to determine the focal length? Explain.

c) For an inverted image is the image height positive or negative?

d) Given the object and image heights and a statement as to whether the image is upright or inverted, what additional information is needed to determine the object distance?

e) A small statue has a height of 3.5 cm and is placed in front of a concave mirror. The image of the statue is inverted, 1.5 cm tall, and is located 13 cm in front of the mirror. Find the focal length of the mirror.

Explanation / Answer

a) the image distance is positive , when the image is in front of a mirror

b) the object distance is also required to find the focal length as

1/f = 1/v + 1/u

c) for an inverted image , the image height will be negative

d) image distance is required to find the object distance

size of image / size of obejct = image distance /object distance

e) -1.5 / 3.5 = 13/u

u = -5.57 cm

1/v + 1/u = 1/f

1/13 -1/5.57 = 1/f

f = -9.74 cm

the focal length of the mirror is 9.74 cm

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