Question

you have to lenses a and b of focal length + 10 centimetre and minus 10 centimetre state the nature and power of each lenses which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens​

Answer 1

Step-by-step explanation:

Given:

• Focal length of lense a, F₁ = + 10 cm = + 0.1 m
• Focal length of lense b, F₂ = - 10 cm = - 0.1 m

In case of lens a,

• Power of lens a, P = 1/F₁
• Power of lens a, P = 1/0.1
• Power of lens a, P = 10/1
• Power of lens a, P = + 10 dioptre or D

Since power is positive, it is convex lens.

In case of lens b,

• Power of lens b, P = 1/F₂
• Power of lens b, P = - 1/0.1
• Power of lens b, P = - 10/1
• Power of lens b, P = - 10 D

Since, power is negative, it is concave lens.

We know that object placed 8 cm from the lens. This distance is less than the distance of focal length 10 cm.

8 cm < 10 cm

So, it is convex lens and will produce virtual and magnified image of an object.

Remember:

In case of convex lens, when we place the object between pole and the focus. The image which is formed is virtual and magnified.

In case of concave lens, when we place the object between pole and the focus, image formed is virtual but diminished.

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