Question

What is meant by power of a lens? You have three lenses L₁, L₂ and L₃ of powers +10D, +5D and -10D respectively.State the nature and focal length of each lens. Explain which of the three lenses will form a virtual and magnified image of an object placed at 15 cm from the lens. Draw the ray diagram in support of your answer.

Answer 1

The ability of a lend to converge or diverge the light rays is called power of a lens.

for lens L₁   P₁=+10D

Since the power is positive the nature of the lens is converging

f₁=1/P₁   f₁=1/10   f₁=0.1m     f₁= +10cm

For lens L₂   P₂=+5D

since the power is positive the nature of the lens is converging

f₂=1/P₂       f₂=1/+5     f₂=0.2m   f₂ =20cm

For lens L₃     P₃= -10D

Since the power is negative the nature of the lens is diverging in nature

f₃= 1/P₃    f₃=1/-10    -0.1m      f₃= -10cm

Lens L₂ will produce virtual erect and enlarged or magnified image because the distance of the object is less than focal length .or the object lies between the optical center and Principal focus.

L₁ will not produce a virtual erect and enlarged image because the object lies between F₁ and 2F₁

L₃ being diverging in nature i.e a concave lens it always produces a virtual erect and diminished image of the object.

Answer 2

Hi there,

The answer is following;

power of lens: The ability of a lend to converge or diverge the light rays.

Lens L₁  

P₁=+10D

Positive sign shows the nature of the lens to be converging.

f₁=1/P₁  

Putting the values of  P₁

f₁=1/10  

f₁=0.1m

f₁= +10cm

Lens L₂   P₂=+5D

as mentioned above, Positive sign shows the nature of the lens to be converging.

f₂=1/P₂      

Putting the values of P₂

f₂=1/+5    

f₂=0.2m  

f₂ =20cm

Lens L₃    

P₃= -10D

Negative sign indicates that the nature of lens is diverging.

f₃= 1/P₃  

Putting the value of p₃  

f₃=1/-10    

-0.1m      

f₃= -10cm

Results

L₁ will not produce a virtual erect and enlarged image because the object lies between F₁ and 2F₁

Lens L₂ will produce virtual erect and enlarged or magnified image because the distance of the object is less than focal length .or the object lies between the optical center and Principal focus.

L₃ being diverging in nature i.e a concave lens it always produces a virtual erect and diminished image of the object.

Thanks for asking