- 1(current)
Q. No.Two identical thin plano-convex glass lenses (refractive index = \(1.5\)) each having radius of curvature of \(20\) cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of a refractive index of \(1.7\). The focal length of the combination is:
| 1. | \(-20\) cm | 2. | \(-25\) cm |
| 3. | \(-50\) cm | 4. | \(50\) cm |
Subtopic: Â Lens Makers' Formula |
 64%
Level 2: 60%+
NEET - 2015
Hints
Links
A plano-convex lens fits exactly into a plano-concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices \(\mu_1\) and \(\mu_2\) and \(R\) is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is:
| 1. | \(\dfrac{R}{2(\mu_1-\mu_2)}\) | 2. | \(\dfrac{R}{(\mu_1-\mu_2)}\) |
| 3. | \(\dfrac{2R}{(\mu_2-\mu_1)}\) | 4. | \(\dfrac{R}{2(\mu_1+\mu_2)}\) |
Subtopic: Â Lens Makers' Formula |
 69%
Level 2: 60%+
AIPMT - 2013
Hints
Links
When a biconvex lens of glass having a refractive index of \(1.47\) is dipped in a liquid, it acts as a plane sheet of glass. The liquid must have a refractive index:
| 1. | equal to that of glass. |
| 2. | less than one. |
| 3. | greater than that of glass. |
| 4. | less than that of glass. |
Subtopic: Â Lens Makers' Formula |
 81%
Level 1: 80%+
AIPMT - 2012
Hints
Links
A biconvex lens \((\mu=1.5)\) has a radius of curvature of magnitude \(20~\text{cm}\). Which one of the following options, best describes, the image formed by an object of height \(2\) cm placed \(30~\text{cm}\) from the lens?
| 1. | virtual, upright, height \(=0.5\) cm |
| 2. | real, inverted, height \(=4\) cm |
| 3. | real, inverted, height \(=1\) cm |
| 4. | virtual, upright, height \(=1\) cm |
Subtopic: Â Lenses |Â Lens Makers' Formula |Â Refraction at Curved Surface |
 71%
Level 2: 60%+
AIPMT - 2011
Hints
Links
- 1(current)
Q. No.
© 2026 GoodEd Technologies Pvt. Ltd.