# HC Verma for Class 11 Physics Chapter 19:Optical Instruments

Chapter 19 Optical Instruments focuses on different objects used to measure optics. The devices that process light waves to enhance the images for a clearer view are called optical instruments. Using optical instruments like a magnifying lens or a complicated device like a microscope and telescope tends to make things under observation bigger. Thus, they help us to see everything clearly. Simply put, converging lenses make things under observation appear larger, whereas diverging lenses minimise the size of things being observed.

If the object is placed at a larger distance while using a converging lens, then the image is diminished. This is because it will be formed very near to the focal point. Conversely, if the object moves in the direction of the lens, the image is seen to move beyond the focal point, and it enlarges in size.

If the object is placed at 2F, i.e., two times the focal distance from the lens, the image and object are observed to be of the same size. However, if the object moves towards the focal point (F) from 2F, the respective image formed continues to move out of the lens and increases in size until it reaches infinite size when the object is at F. So, as the object moves closer to the lens, the image moves in the direction of the lens from negative infinity and gets smaller when the object gets closer to the lens.

There are various optical instruments we use in our daily life. They include cameras, microscopes, telescopes, and so on. For example, when parallel rays of light enter a relaxed eye, the rays may be brought to focus before entering the retina. Thus, it is usually simpler to see objects that are located close. However, the light from them might be brought to a focus too soon when it comes to objects located afar. In such cases, the eye is said to be myopic or near-sighted.