Question

A converging lens is used to project a 250 mm image of a square slide onto a screen 1000 mm away. the focal length of the lens is 200 mm. by means of scale drawing, determine---(a) the distance of the slide from the lens----(b) the size of the slide???

please explain it to me...

Answer 1

(a)Distance of the slide from lens = 250 mm

(b) The size of the slide = 62.5 mm

Explanation:

Given

• `s_i->"Size of the image"=250mm`
• `v->"Image distance"=+1000mm`
• `f-> "Focal length of convex lens"=+200mm`

We are to find out

• `u->"object distance"=?`

• `s_o->"Size of the object"=?`

Calculation

Lens formula

`color(blue)(1/v-1/u=1/f)`

Plugging the values

`=>1/1000-1/u=1/200`

`=>1/u=1/1000-1/200=(1-5)/1000=-1/250`

`color(red)(=>u=-250mm)`

`color(green)("-ve sign means real object")`

Now magnification (m)

`m = s_i/s_o=v/u`

`=>250/s_o=1000/250=4`

`color(red)(=>s_o=250/4=62.5mm)`

The distance of the slide from lens (u)=250mm.

The size of the slide =62.5mm