Last Updated on October 23, 2024 by XAM CONTENT

Hello students, here you will find numerical on refraction through a lens with answers. Before we start solving the numerical, let’s see some important points and formulae. This will help you to solve the problems efficiently.

### Understanding Refraction Through a Lens

Refraction is the bending of light as it passes from one medium to another due to a change in its speed. Lenses, which are made of transparent materials, utilize refraction to converge or diverge light rays. Understanding how refraction occurs in lenses is crucial in optics, as it forms the basis for many applications like glasses, cameras, microscopes, and telescopes.

In the below section, we are providing numerical problems based on Refraction Through a Lens for Class 12 Physics.

### Refraction Through a Lens Class 12 Physics Numerical with Answers

**Formula used:**

Question 1: A double convex lens has radii of curvature 20 and 30 cm respectively and refractive index of the material is 1.5 . What will be its focal length in air and in water of refractive index $4 / 3$.

[Ans. $24 \mathrm{~cm} ; 96 \mathrm{~cm}$ ]

Question 2: A convex lens of focal length 30 cm and made of glass $\mu=1.50$ is immersed in a liquid of refractive index $4 / 3$. Find the change in the focal length of the lens.

[Ans. 90 cm]

Question 3: A symmetrical bi-convex lens has a focal length of 30 cm. Calculate the radius of the curvature of either face if the refractive index of the material of the lens is 1.51.

[Ans. 30.6 cm]

Question 4: Calculate the focal length of an equiconvex lens $\left(R_1=R_2=R\right)$ made of glass with refractive index 1.5 and $R=1$ metre.

[Ans. 1 metre]

Question 5: The radius of curvature of the convex surface of a plano-convex lens is 12 cm and refractive index of the material is 1.5. Find the focal length of the lens.

[Ans. 24 cm]

Question 6: A convex lens of focal length (i) 30 cm (ii) 20 cm and made of glass $(\mu=1.5)$ is immersed in a liquid ($\mu$ $=1.33$); find the change in focal length in each case.

[Ans. $87.35 \mathrm{~cm}; 58.23 \mathrm{~cm}$]

Question 7: The two surfaces of a double concave lens are of curvature 10 cm and 40 cm. Find the focal length of the lens in water. The refractive index of water is $4 / 3$ and that of the material of lens is $3 / 2$.

[Ans. $-64 \mathrm{~cm}]$

Question 8: A plano-convex lens is silvered on its plane side and acts like a concave mirror of 20 cm focal length. When convex side is silvered it acts like a concave mirror of 7 cm focal length. Calculate the refractive index of the material of lens, and radius of curvature of the curved surface.

[Ans. $1.54; R=21.56 \mathrm{~cm}]$

Question 9: One surface of a convergent lens of 20 cm focal length is convex and has a radius of curvature 25 cm. If the refractive index of glass of which the lens is made is 1.5, what is the radius of curvature of the other surface?

[Ans. 16.67 cm$]$

We hope the given numerical on Refraction Through a Lens Class 12 Physics helps you in your learning.

For further practice on numerical problems related to Refraction Through a Lens Class 12 Physics, we recommend exploring the link given below.

### Frequently Asked Questions (FAQs) on Refraction Through a Lens Class 12 Physics

#### Q1: **What is refraction in the context of lenses?**

A1: Refraction is the bending of light as it passes from one medium to another with different densities, such as from air into glass. In lenses, refraction causes light rays to either converge or diverge, forming images.

#### Q2: **What are the two types of lenses based on refraction?**

A2: The two main types of lenses are:**Convex Lens (Converging Lens):** Bends light rays inward, causing them to converge at a point.**Concave Lens (Diverging Lens):** Bends light rays outward, making them appear to diverge from a point.

#### Q3: **How does a convex lens form an image?**

A3: A convex lens bends parallel light rays toward a focal point. The image formed can be real (inverted and formed on the opposite side) or virtual (upright and formed on the same side), depending on the object’s distance from the lens.

#### Q4: **What is the focal length of a lens?**

A4: The focal length is the distance between the center of the lens and the focal point where parallel light rays converge or appear to diverge. A shorter focal length means the lens is more powerful in bending light.

#### Q5: What is magnification in a lens?

A5: Magnification refers to how much larger or smaller the image is compared to the object.

#### Q6: **What is the difference between real and virtual images in lenses?**

A6: **Real Image:** Formed when light rays converge; the image is inverted and can be projected onto a screen (common with convex lenses).**Virtual Image:** Formed when light rays appear to diverge; the image is upright and cannot be projected (common with concave lenses).