Question

The focal lengths of four convex lenses P, Q, R and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. lens having greatest power is:; A. P; B. Q; C. R; D. S

Answer 1

Answer:

c. r

Explanation:

c. r option is correct

Answer 2

Answer:

(C) R has highest power.

Explanation:

In the question,

We know that the Power of the lens is given by,

$P = \frac{1}{f}$

where,

P is the Power of the lens.

and,

f = Focal length of given lens (in metres).

So,

For the Lens P,

Focal length, f = 20 cm

So,

$P=\frac{1}{20\times 10^{-2}}\\P=5\ D$

Therefore, the Power is 5 Dioptres.

For the lens Q,

Focal length, f = 15 cm

So,

$P=\frac{1}{15\times 10^{-2}}\\P=6.666\ D$

Therefore, the Power is 6.66 Dioptres.

For the lens R,

Focal length, f = 5 cm

So,

$P=\frac{1}{5\times 10^{-2}}\\P=20\ D$

Therefore, the Power is 20 Dioptres.

For the lens S,

Focal length, f = 10 cm

So,

$P=\frac{1}{10\times 10^{-2}}\\P=10\ D$

Therefore, the Power is given by 10 Dioptres.

So,

The Highest power is of lens R.