Question

An object is placed 3cm in front of a diverging lens of focal length of 6cm. the heihgt of the object is 1.5 cm. calculate the image distance and height

Answer 1

-1/6-1/3=-1/2
image distance=-2

hi/ho=-di/do
hi/1.5=-(-2)/3
hi=(2/3)x(3/2)
hi=1

Answer 2

i want to know the formula according to conventions as i saw two different systems as i studied.

Answer 3

For convex and concave lens and for concave and convex mirror
the formula is

1/ di + 1/do = 1/f

m = hi/ho = - di /do


Note that different conventions are in practice .

Accordingly the formula will change .

For the above formula the following sign conventions are used.

• f is + if the lens is a double convex lens (converging lens)
• f is - if the lens is a double concave lens (diverging lens)
• di is + if the image is a real image and located on the opposite side of the lens.
• di is - if the image is a virtual image and located on the object's side of the lens.
• hi is + if the image is an upright image (and therefore, also virtual)
• hi is - if the image an inverted image (and therefore, also real)
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For concave and convex mirror
• f is + if the mirror is a concave mirror
• f is - if the mirror is a convex mirror
• di is + if the image is a real image and located on the object's side of the mirror.
• di is - if the image is a virtual image and located behind the mirror.
• hi is + if the image is an upright image (and therefore, also virtual)
• hi is - if the image an inverted image (and therefore, also real)