Test: Refraction through Spherical Lense - Class 10 MCQ

The focal length of convex lens is always positive. Image obtained can be either real or virtual.

For focal length, f in lens is always taken as negative for concave lens and positive for convex lens.

Convex (converging) lenses can form either real or virtual images (cases 1 and 2, respectively), whereas concave (diverging) lenses can form only virtual images (always case 3). Real images are always inverted, but they can be either larger or smaller than the object.

At the 2F point, the object distance equals the image distance and the object height equals the image height. As the object distance approaches one focal length, the image distance and image height approaches infinity.

Concave lenses are thinner at the middle. Rays of light that pass through the lens are spread out (they diverge). A concave lens is a diverging lens. When parallel rays of light pass through a concave lens the refracted rays diverge so that they appear to come from one point called the principal focus.

A concave lens (also known as a diverging lens) is thinner in the center and thicker at the edges. When light rays pass through a concave lens, they diverge (spread out), causing the rays to appear to come from a single point on the same side of the lens as the object. This results in the formation of a virtual image.

Key characteristics of the image formed by a concave lens:

• Diminished: The image is smaller than the actual object.
• Erect: The image is upright, meaning it has the same orientation as the object.
• Virtual: The image cannot be projected on a screen because the light rays do not actually meet but only appear to do so when extended backward.

Because of these properties, a concave lens always forms a diminished, erect, and virtual image, no matter where the object is placed in front of the lens.

On the other hand, a convex lens (also known as a converging lens) can form different types of images (real and inverted or virtual and erect) depending on the position of the object relative to the lens. But it does not always form a diminished and erect image, unlike the concave lens.

A ray of light passes through optical centre of a lens is refracted back along the same path ie. through optical centre itself.

The order of decreasing accuracy in measurement of focal length of convex lens by the given techniques is DBCA.

D - Student D used a well illuminated distant tree as the object and a white thick board held on a stand, as the screen. This technique is more accurate than Student A's technique because the object is a distant tree, which provides a nearly parallel beam of light, and the screen is held on a stand.

B - Student B used a distant tree in absence of sunlight as the object, and a white thick board held on a stand, as the screen. This technique is also quite accurate as the object is a distant tree, which provides a nearly parallel beam of light, and the screen is held on a stand.

C - Student C used a well illuminated laboratory window grill as the object and a white paper sheet held on a stand as the screen. This technique is more accurate than Student B's technique because the object is well-illuminated and the screen is held on a stand, which minimizes any movements or vibrations that could affect the measurement.

A - Student A used the window grill in the laboratory as the object and a white paper sheet held in hand, as the screen. This technique is the least accurate because the object is the window grill in the laboratory, which may not provide a sufficiently distant or parallel beam of light, and the screen is held in hand, which could lead to some movements and vibrations that could affect the measurement.

At twice the focal length the image formed by convex lens is real and of the same size as object.

Let the distance between the object and its real image formed by convex lens be d₁​.
Let the distance of the object from lens be x,so,the image distance from the lens is (d-x)

The minimum distance between an object and its real image in a convex lens is 4f.
hence,option C is correct.
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The surface of a water drop curves outward to make a dome. This outward, or convex, curvature bends light rays inward.  will act as a concave lens that bends the light rays outward. As a result, letters seen through the layer of water in a cup appear smaller than they are.

The image formed by a convex lens is observed to be virtual, erect and larger than the object. Then the position of the object should be. If the object is placed between the pole and focus, then the image formed will be virtual, erect and enlarged.

Shortsightedness is corrected using a concave (curved inwards) lens which is placed in front of a myopic eye, moving the image back to the retina and making it clearer.