Study the given ray diagrams and select the correct statement from the following:
Device X is a concave mirror and device Y is a convex lens, whose focal lengths are 20 cm and 25 cm respectively.
Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 10 cm and 25 cm respectively.
Device X is a concave lens and device Y is a convex mirror, whose focal lengths are 20 cm and 25 cm respectively.
Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.
(4)
Since, for device X the light rays are coming from an object at infinity, passes through the device X and forms a real image on a screen on right side. Since, convex lens forms a real and inverted image at focus when object is at infinity. So, device X is converging lens or convex lens of focal length 20 cm.
For device Y, the beam of parallel rays from infinity is incident on the left side and after reflection a real image is formed on the screen. This device should be a mirror. Also, the light rays are getting converged, so mirror is converging in nature; it is a concave mirror of focal length 25 cm.
A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens :
away from the screen
towards the screen
to a position very far away from the screen.
either towards or away from the screen depending upon the position of the object.
(2)
As in order to get a sharp image the screen should be near to lens.
Suppose you have focussed on a screen the image of candle flame placed at the farthest end of the laboratory table using a convex lens. If your teacher suggests you to focus the parallel rays of the Sun, reaching your laboratory table, on the same screen, what you are expected to do is to move the :
lens slightly towards the screen
lens slightly away from the screen
lens slightly towards the sun
lens and screen both towards the sun
(1)
Since, candle is at the farthest end but not at the infinity. So, image will be formed between focus and centre of curvature of lens, but parallel rays from sun will converge at the focus. So, the distance between lens and screen should be reduced to get the image of the Sun.
Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?
15 cm in front of the mirror
30 cm in front of the mirror
Between 15 cm and 30 cm in front of the mirror
More than 30 cm in front of the mirror
(2)
In case of a concave mirror, image size becomes equal to the object size when the object distance equals to the radius of curvature i.e., twice the focal length.
So, the object has to be placed at a distance of (15 × 2) = 30 cm in front of a concave mirror.
Which of the following statement is incorrect?
The bending of a ray of light on passing from different media to one is called reflection.
The phenomenon of splitting of white light into seven constituent colours is known as the dispersion of light.
Refractive index of medium depends upon its temperature.
Refractive index is directly proportional to the density of the medium.
(1)
Bending of a ray of light on passing from one media to another is called refraction.
A piece of red cloth when suitably illuminated may look black, but a piece of black cloth will never appear red. This phenomenon occurs because :
Black cloth reflects only black light
Black absorbs all the colours
Black cloth reflects all colours
Red cloth reflects all colours
(2)
Black colour is a good absorber.
Consider four mediums P, Q, R and S whose refractive indices are 2.14, 1.99, 2.98, and 2.16 respectively. Assume that if light travels from one medium to another. The rate of change will be utmost in which medium.
P to Q
Q to R
R to S
S to P
(2)
As the difference in refractive indices is maximum.
The refractive index of a colourless, volatile, non-polar solvent is 1.24 to the refractive index of a solid ice cube. The unmitigated refractive index of the ice cube is 1.31. Enumerate the unmitigated refractive index of the non-polar solvent.
1.6522
1.3241
1.6244
1.2401
(3)
Which of the following mirror is used by a dentist to examine a small cavity?
Convex mirror
Plane mirror
Concave mirror
Combination of convex and concave mirror
(3)
As concave mirror gives the dentist a magnified reflection of the mouth while also refracting a bit of light. It forms an image in the mirror as larger, brightened and for the dentist easier to see.
When light falls on a smooth polished surface, most of it
Is reflected in the same direction
Is reflected in different direction
Is scattered in all direction
Is refracted into the second medium
(1)
This type of reflection is known as regular or specular reflection.
