If a lens has a focal length, F = +12 cm, then it is a
The focal length of convex lens is always positive. Image obtained can be either real or virtual.
If a lens has a focal length, f = -12 cm. then it is a
For focal length, f in lens is always taken as negative for concave lens and positive for convex lens.
Which lens always forms a virtual image ?
A concave lens always form a virtual image of an object because it diverges all parallel rays so that they appear to come front focus on the other side of the lens.
In a convex lens, where is the image formed, when an object is placed at 2F ?
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.
What happens to the image formed by a convex lens if its lower part is blackened ?
Which lens has a virtual focus ?
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.
Which lens always forms diminished and erect image ?
A ray of light incident on the optical centre of a spherical lens, after refraction passes through:
A ray of light passes through optical centre of a lens is refracted back along the same path ie. through optical centre itself.
The focal length of a concave lens is:
Four students A, B, C and D did their experiment on finding the focal length of convex lens by obtaining the image of a distant object as follows:
Student A used the window grill in the laboratory as the object and a white paper sheet held in hand, as the screen.
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.
Student C used a well illuminated laboratory window grill as the object and a white paper sheet held on a stand as the screen.
Student D used a well illuminated distant tree as the object and a white thick board held on a stand, as the screen.
Arrange these techniques in order of decreasing accuracy in measurement.
In case of convex lens rays coming from infinity meet at focus so a well illuminated distant tree can be a object and white thick board can be used as screen to obtain the image.
A magnifying glass is a
Is the optical centre always at the centre of lens ?
Where should an object be placed in front of a convex lens to get a real image of the size of the object ?
At twice the focal length the image formed by convex lens is real and of the same size as object.
The minimum distance between an object and its real image in a convex lens is (f = focal length of the lens)
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.
The image formed by a convex lens is virtual when
Drop of water behaves likes a
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.
A lens which forms a virtual and enlarged image is
To determine the focal length of convex lens by obtaining a sharp image of a distant object we generally follow the following steps which are not in proper sequence.
(a) Hold the lens between the object and the screen
(b) Measure the distance between the lens and the screen
(c) Select a well lit distant object
(d) Adjust the position of the lens to form a sharp image
The correct sequence will be:
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
The lens which is used to correct myopia (shortsightedness) is
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.