a convex lens of focal lenght 20 cm is placed in contact with concave lens 10 cm what is focal lenght and far of combination
Answers
Correct Question!!
• A convex lens of focal lenght 20 cm is placed in contact with concave lens 10 cm what is the Power of combination of lens.
Given:-
- Focal length of Convex lens ,f1 =+20cm
- Focal length of concave lens ,f2 = -10 cm
To Find:-
- Power of Combination of lens ,P.
Solution:-
As we know that the SI unit of length is metre.
So we change the Unit of Focal length
For convex Lens
→ f1 = 20/100m
→ f1 = +0.5 m
For Concave Lens
→ f2 = -10/100m
→ f2 = -0.1m
Now Power of combination
As we know that Power of a lens is the reciprocal of its focal length
• P = 1/f
Power of Convex Lens
→ P1 = 1/0.5
→ P1 = 10/5
→ P1 = 2 D
Power of Concave Lens
→ P2 = 1/f2
→ P2 = -1/0.1
→ P2 = -10/1
→ P2 = -10 D
So, Power of Combination
• P = P1 + P2
Substitute the value we get
→ P = 2D + (-10) D
→ P = 2D - 10D
→ P = -8D
Therefore, the power of the combination of the lens is -8 Dioptre.
Correct Question!!!!
》A convex lens of focal lenght 20 cm is placed in contact with concave lens 10 cm what is the power of combination of lens.
Correct Answer!!!!
Give data:
Focal length of Convex lens ,f1 =+20cm
Focal length of concave lens ,f2 = -10 cm
To find:
Power of combination of lens = P = ?
Solution:
As we know that the SI unit of length is metre.
So we change the Unit of Focal length
For convex Lens
=> f1 = 20/100m
=> f1 = +0.5 m
For Concave Lens
=>f2 = -10/100m
=> f2 = -0.1m
Now Power of combination
As we know that Power of a lens is the reciprocal of its focal length
☆P = 1/f
Power of Convex Lens
=>P1 = 1/0.5
=> P1 = 10/5
=> P1 = 2 D
Power of Concave Lens
=>P2 = 1/f2
=> P2 = -1/0.1
=> P2 = -10/1
=> P2 = -10 D
So, Power of Combination
☆ P = P1 + P2
Substitute the value we get
=> P = 2D + (-10) D
=> P = 2D - 10D
=> P = -8D
Power of the combination of the lens is -8 Dioptre
Hope so it will help......