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The experiment “Image of an Object Between F and 2F of Convex Lens” aims to study the refraction of light through a lens. The objective of this experiment is to observe the image formed for an object placed between the focus and the centre of curvature of a convex lens.
How Are Images Formed By a Convex Lens?
A convex lens bulges outward and is thicker in the middle and thinner at the upper and lower edges. A convex lens forms images through the refraction of light passing through it. When refracted through a convex lens, the light rays obey the laws of refraction. A convex lens converges the light rays parallel to the principal axis towards the focal point, as shown in the figure below:
Hence, convex lenses are called converging lenses.
Light rays passing through the edges of a convex lens are bent most, whereas light passing through the lens’s centre remains straight.
A convex lens forms either a real or virtual image. It depends on how close the object is to the lens relative to the focus.
- Case 1: A real, inverted image will be formed for an object outside the focal point.
- Case 2: For an object inside the focal point, a virtual erect image will be formed.
Convex lenses are the only lenses that can form real images. Unlike a virtual image, a real image appears where the light converges.
When the object is placed at a distance less than 2f but more than f from the optical centre of the convex lens, we obtain a real, inverted and enlarged image on the screen.
The image’s nature, position, and size can be noted and measured from the optical centre O of the thin convex lens, as shown in the figure below:
What Are The Rules For Image Formed By a Convex Lens?
For drawing ray diagrams, only two rays are considered for clarity. The intersection of at least two refracted rays gives the position of the image of the point object. Any two of the following rays can be considered for locating the image:
- Rule 1: An incident ray travelling parallel to the principal axis after refraction through the convex lens passes through the focal point on the other side.
- Rule 2: An incident ray passing through the first principal focus of a convex lens emerges parallel to the principal axis after refraction.
- Rule 3: A ray of light, passing through the optical centre of the lens, emerges without any deviation after refraction.
FAQs on Image of an Object Between F and 2F of Convex Lens
Q.1 A convex lens of focal length 20 cm can produce a magnified real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?
Ans. This is the correct statement. When an object is placed between F and 2F of a convex lens, its enlarged, inverted, and real image is formed beyond 2F on the other side of the lens. So, for this, we need to place the object between 20cm and 40cm of the lens.
Q.2 Give any three examples of devices in which a convex lens is used.
Ans. Convex lenses are used in telescopes, microscopes, and projectors.
Q.3 Can a convex lens produce virtual images?
Ans. A Convex lens can form either real or virtual images depending on the object’s position.
Q.4 What is the nature of the image formed by a convex lens if the magnification produced by a convex lens is -3?
Ans. Since magnification is negative, the image formed is inverted and real. Also, it is enlarged and three times the size of the object.
Q.5 If we cover one-half of the convex lens while focusing on a distant object, in what way will it affect the image formed?
Ans. When we cover one-half of the convex lens, say with black paper, an image will be formed as in the case of the normal lens; only the brightness or intensity of the light will be diminished due to the covering of black paper.
JEE Main