Two lenses A and B have focal lengths of +20cm and, -10cm, respectively. 1. What is the nature of lens A and lens B? 2. What is the power of lens A and lens B? 3. What is the power of combination if lenses A and B are held close together?

$f _{ A }=+20 cm=+0.2 m f _{ B }=-10 cm=-0.1 m$ 1. Lens A is a convex lens (positive focal length) and lens B is a concave lens (negative focal length). 2. $\text{P}_\text{A}=\frac{1}{\text{f}_\text{A}}=\frac{1}{+0.2}=+5\text{D}$ $\text{P}_\text{B}=\frac{1}{\text{f}_\text{B}}=\frac{1}{-0.1}=-10\text{D}$ 3. Power of combination, P = PA + PB = +5D + (-10D) = -5D

Two lenses A and B have focal lengths of +20cm and, -10cm, respectively. 1. What is the nature of lens A and lens B? 2. What is the power of lens A and lens B? 3. What is the power of combination if lenses A and B are held close together?

$f _{ A }=+20 cm=+0.2 m f _{ B }=-10 cm=-0.1 m$ 1. Lens A is a convex lens (positive focal length) and lens B is a concave lens (negative focal length). 2. $\text{P}_\text{A}=\frac{1}{\text{f}_\text{A}}=\frac{1}{+0.2}=+5\text{D}$ $\text{P}_\text{B}=\frac{1}{\text{f}_\text{B}}=\frac{1}{-0.1}=-10\text{D}$ 3. Power of combination, P = PA + PB = +5D + (-10D) = -5D

Two lenses A and B have focal lengths of +20cm and, -10cm, respectively. 1. What is the nature of lens A and lens B? 2. What is the power of lens A and lens B? 3. What is the power of combination if lenses A and B are held close together?

$f _{ A }=+20 cm=+0.2 m f _{ B }=-10 cm=-0.1 m$ 1. Lens A is a convex lens (positive focal length) and lens B is a concave lens (negative focal length). 2. $\text{P}_\text{A}=\frac{1}{\text{f}_\text{A}}=\frac{1}{+0.2}=+5\text{D}$ $\text{P}_\text{B}=\frac{1}{\text{f}_\text{B}}=\frac{1}{-0.1}=-10\text{D}$ 3. Power of combination, P = PA + PB = +5D + (-10D) = -5D

Two lenses A and B have focal lengths of +20cm and, -10cm, respectively. 1. What is the nature of lens A and lens B? 2.

[3 Mark Questions]

CBSE - English Medium

Two lenses A and B have focal lengths of +20cm and, -10cm, respectively.

What is the nature of lens A and lens B?
What is the power of lens A and lens B?
What is the power of combination if lenses A and B are held close together?

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Solution

$f _{ A }=+20 cm=+0.2 m f _{ B }=-10 cm=-0.1 m$

Lens A is a convex lens (positive focal length) and lens B is a concave lens (negative focal length).
$\text{P}_\text{A}=\frac{1}{\text{f}_\text{A}}=\frac{1}{+0.2}=+5\text{D}$

$\text{P}_\text{B}=\frac{1}{\text{f}_\text{B}}=\frac{1}{-0.1}=-10\text{D}$

Power of combination,

P = PA + PB = +5D + (-10D) = -5D

STD 10
Science
Light – Reflection and Refraction
NCERT

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