What is the focal length of combination of two lenses?
What is the focal length of combination of two lenses?
The distance from the second lens to the focal point of the combined lenses is called the back focal length (BFL). BFL=f2(d−f1)d−(f1+f2) BFL = f 2 ( d − f 1 ) d − ( f 1 + f 2 ) . As d tends to zero, the value of the BFL tends to the value of f given for thin lenses in contact.
What is the power of combination of two lenses of focal length 10cm and?
So, the effective power of combination is 30 cm.
When two convex lenses are put in contact the focal length of the combination is?
The focal length of the combination of two convex lens in contact is f and if they are separated by a distance, then focal length of the combination is f1.
What is combination lens?
Combination of lenses. When two lenses are used in combination, the first one forms an image that then serves as the object for the second lens. The magnification of the combination is the ratio of the height of the final image to the height of the object. This is the final image produced by the combination of lenses.
Where is combination of lenses used?
Combination of lenses is used in various optical instruments because: (i) To increase the magnification of the image. (ii) To increase the sharpness of the image. (iii) To make the final image erect.
How do you find the combination of a lens?
Expert Answer:
- Power of concave lens = 100/20 = 5 D.
- Power of convexs lens = -100/30 D.
- Power of combined lens = (100/20) – (100/30) D = 100/60 D.
- focal length of combined lens = 60 cm.
What if half portion of lens or mirror is covered with black paper?
The image produced will be complete. But the image observed now will be fainter. Even when half of the mirror is covered with black paper, it would still produce a complete image but the image produced would be fainter (of lesser intensity) than the image produced when half mirror was not covered.
Does the focal length of a lens change on changing the object distance?
Answer: No, as focal length doesn’t depend on object distance. It depends on centre of curvature and refractive index of material used in making the lens.
When two lenses of power 4D and 3D are placed in contact The power of the resultant lens is?
Here: Power of convex lens = 4D Power of concave lens = 3D Hence, die equivalent power of the combination = 4D – 3D = 1D ( ∵ Concave lens has negative (minus) focal length, so its power will also be negative.)
What is the focal length of a lens of power 1D?
One dioptre is the power of the lens whose focal length is 1m.
What is thin lens combination?
Power of a lens is a measure of the degree of convergence or divergence of light falling on it. The power of a lens (P) is defined as the reciprocal of its focal length. The unit of power is dioptre (D) : 1 D = 1 m-1.