In an experiment to determine the focal length of a convex lens, a student obtained the image of a distant window on the screen. To determine the focal length of the lens, she should measure the distant between the ____.
lens and the screen only.
lens and the window only.
screen and the window only.
screen and the lens and also between the screen and the window.
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 grille in the laboratory as the object and a white paper sheet held in hand, as the screen.
Student B. Used a distant tree in the shade as the object, and a white thick board held in a stand, as the screen.
Student C. Used well illuminated laboratory window grilles as the object and a white paper sheet held in a stand as the screen.
Student D. Used a well illuminated distant tree a s the object and a white thick board held in a stand, as the screen.
Which one of the four sequences of above set-ups represents the correct decreasing order to performance for performing the experiment?
D, B, C, A
C, D, A, B
D, C, A, B
B, D, C, A
The focal lengths of convex lens for red and blue light are 100 cm and 96.8 cm respectively. The dispersive power of material of lens is ____.
0.325
0.0325
0.98
0.968
The power of an achromatic convergent lens of two lenses is + 2D. The power of convex lens is + 5D. The ratio of dispersive power of convex and concave lens is ____.
5 : 3
3 : 5
2 : 5
5 : 2
The focal lengths for violet, green and red light rays are and respectively. Which of the following is the true relationship?
When light rays from the sun fall on a convex lens along a direction parallel to its axis ____.
focal length for all colours is the same
focal length for violet colour is the shortest
focal length for yellow colour is the longest
focal length for red colour is the shortest
A convex lens is in contact with concave lens. The magnitude of the ratio of their focal length is 2/3. Their equivalent focal length is 30 cm. What are their individual focal lengths?
– 75, 50
– 10, 15
75, 50
– 15, 10
A thin glass (refractive index 1.5) lens has optical power of in air. It's optical power in a liquid medium with refractive index 1.6 is ____.
25 D
– 25 D
1 D
None of the above
The plane faces of two identical Plano-convex lenses each having focal length of 40 cm are pressed against each other to form a usual convex lens. The distance from this lens, at which an object must be placed to obtain a real, inverted image with magnification one is ____.
80 cm
40 cm
20 cm
162 cm
A concave lens and a convex lens have same focal length of 20 cm and both put in contact this combination is used to view an object 5 cm long kept at 20 cm from the lens combination. As compared to object the image is ____.
magnified and inverted
reduced and erect
of the same size and erect
of the same size and inverted
The focal length of the field lens (which is an achromatic combination of two lenses) of telescope is 90 cm. The dispersive powers of the two lenses in the combination are 0.024 and 0.036. The focal lengths of two lenses are ____.
30 cm and 60 cm
30 cm and – 45 cm
45 cm and 90 cm
15 cm and 45 cm
A combination of two thin lenses of the same material with focal lengths and , arranged on a common axis minimizes chromatic aberration, if the distance between them is ____.
If the focal length of a double convex lens for red light is its focal length for the violet light is ____.