Posted by **hunar** on Wednesday, December 12, 2012 at 11:52am.

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

- physics -
**pking**, Wednesday, December 12, 2012 at 11:53am
-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

- physics -
**hunar**, Wednesday, December 12, 2012 at 11:54am
i want to know the formula according to conventions as i saw two different systems as i studied.

- physics -
**justiin**, Wednesday, December 12, 2012 at 11:55am
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)

=================================

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)

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