Question

what is meant by power of a lens ? you have three lens L1 ,L2, 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

★Power of a lens is the degree of convergence of divergence of light rays achieved by a lens.

**Lens L1 : f1

= +10 cm ; Convex lens

**Lens L2 : f2

= +20 cm ; Convex lens

**Lens L3 : f3

= -10 cm ; Concave lens

★Lens L2 will form a virtual and magnified image of an object placed at 15 cm from the

convex lens because concave lens can never form virtual and magnified image of an object and convex lens form such image only when the object is placed between the optical centre and principle focus of the convex lens

MAY THIS HELP U MY FRND!!!!❤️❤️

Answer 2

The answers to the questions about lenses are as follows:

Power of Lens:

• The measure of the degree of convergence or divergence is the power of the lens.

• In simple words, it refers to the reciprocal of the focal length

• The SI unit of focal length is Dioptre or m⁻¹. Its formula is given by

                               Power of a lens = 1/f Dioptre or m⁻

Nature and focal length of lens L₁, L₂, L₃:

Given:

L₁ = +10D

L₂ = +5D

L₃ = -10D

To Find:

The nature and focal length of L₁, L₂, L₃

The lens forms a virtual and magnified image of an object placed at 15 cm from the lens and ray diagram of the respective lens.

Solution:

P₁ = + 10D (Convex lens)

f₁ = 1/P

f₁ = 1/10

f₁ = 0.1m

Therefore, the lens L₁ is a convex lens and its focal length is 0.1m

P₂ = 5D (Convex Lens)

f₂ = 0.2m

Therefore, the lens L₂ is a convex lens and its focal length is 0.2m

P₃ = -10D (Concave Lens)

f₃ = 0.1m

Therefore, the lens L₃ is a concave lens and its focal length is 0.1m

The lens L₂ will form the virtual and magnified image when an object is placed 15cm from the lens. This is because a concave lens can never form a virtual and magnified image.

However, a convex lens forms such an image only when the object is placed between the optical center and the principle focus of the convex lens.

The image of the ray diagram supporting the answer is attached below.

Therefore, the L₂ lens forms a virtual and magnified image when an object is placed at 15cm.

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