Question

1). where should an object be placed from covering lens of focal length 20 CM so as to obtain a real image of magnification 2?
2). a convex lens is used to throw on a screen 10 centimetre from the lens and magnified image of an object if the magnification is to be 19 find the focal length of the lens?
3). at what distance should an object be placed from a convex lens of focal length 15 cm to 3 M is 3 times the small the size of the object?
it's all of them are Optics Numerical please now it's urgent pleaseeee
I Mark brain list for your answering........

Answer 1

Hi,

1) ans ;
Ans.30 cm before the lens

Magnification M =-2 ( real and inverted image)

M = v / u =-2
V=-2u ....eq (1)

From lens formula
1/f = 1/v - 1/u  .....eq (2)

Given f = 20cm

On substitution of eq (1) in (2)  we get  U = - 30 cm  ( it is negative from the sign convention)





(2) ans ;

v =10m 

Real image is formed on screen, so image is inversed. 
(the detailed answer is in top image)





(3) ans;
focal length = f = 15cm

Height of image (hi) = 3 x height of object (hi)

q = 3p (where q is image distance and p is object distace) ; As hi/ho = q/p

p = ??

1/f = 1/p + 1/q (formula)

1/15 = 1/p + 1/3p

1/15 = 4/3p

p = 15(4)/3

p = 20cm

Result: object distance is 20cm from the lens.



HOPE THIS HELPS YOU!

Be Brainly@

Answer 2

Ans.30 cm before the lens

Magnification M =-2 ( real and inverted image)

M = v / u =-2
V=-2u ....eq (1)

From lens formula
1/f = 1/v - 1/u  .....eq (2)

Given f = 20cm

On substitution of eq (1) in (2)  we get  U = - 30 cm  ( it is negative from the sign convention


 

v =10m 

Real image is formed on screen, so image is inversed

the add pic solution no2

3.


focal length = f = 15cm

Height of image (hi) = 3 x height of object (hi)

q = 3p (where q is image distance and p is object distace) ; As hi/ho = q/p

p = ??

1/f = 1/p + 1/q (formula)

1/15 = 1/p + 1/3p

1/15 = 4/3p

p = 15(4)/3

p = 20cm

Result: object distance is 20cm from the lens.