the focal length of a concave mirror is 30cm. find the position of the object in front of the mirror so that the image is three times the size of the object.
PLZ do it quickly.. I need it urgent
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Hey Tania,
Mirror formula:1/v+1/u=1/f
=>(u+v)/uv=1/f
Multiplying by u we get ,
=>(u+v)/v=u/f
=>u/v+v/v=u/f
=>u/v=u/f-1
=>u/v=(u-f)/f
=>v/u=f/(u-f)
=>M=-v/u=f/(f-u) ....(I)
We have derived a new formula.
As magnification is 3 ,it is always real,inverted and M=-3.
Now,M=-3,f=-20(by sign convention)
Putting in eq(I)we get,
=>-3=-20/(-20-u)
=>60+3u=-20
=>3u=-80
=>u=-80/3.
Hope it helps.
Mirror formula:1/v+1/u=1/f
=>(u+v)/uv=1/f
Multiplying by u we get ,
=>(u+v)/v=u/f
=>u/v+v/v=u/f
=>u/v=u/f-1
=>u/v=(u-f)/f
=>v/u=f/(u-f)
=>M=-v/u=f/(f-u) ....(I)
We have derived a new formula.
As magnification is 3 ,it is always real,inverted and M=-3.
Now,M=-3,f=-20(by sign convention)
Putting in eq(I)we get,
=>-3=-20/(-20-u)
=>60+3u=-20
=>3u=-80
=>u=-80/3.
Hope it helps.
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