Test: Ray Optics - 2 - Class 10 MCQ

The dispersion of light is the phenomenon of splitting of a beam of white light into its seven constituent colours when passed through a transparent medium. It was discovered by Isaac Newton in 1666. Newton discovered that light is made up of seven different colours. He passed a beam of sunlight through a glass prism. The glass prism split the light into a band of seven colours on his wall. He called this band of colours the ‘spectrum’. Thus the spectrum is a band of seven colours which is obtained by splitting of white light by a glass prism. The order of colours from the lower end of spectrum is violet (V), indigo (I), blue (B), green (G), yellow (Y), orange (O), and red (R). The sequence of the 7 colours so obtained in a spectrum can be remembered by using the acronym ‘VIBGYOR’. 

Frequency of light does not change on refraction, when a ray of light passes from one medium to another, it's direction changes because of change in speed of light from one medium to another. 

The bending of light as it passes from one medium to another is called refraction. The angle and wavelength at which the light enters a substance and the density of that substance determine how much the light is refracted. The bending occurs because light travels more slowly in a denser medium.

Hence, by a glass prism as well as a rectangular glass slab

In order to see full image of a person, the minimum size of the mirror should be one half the person's height. This is so because, in reflection, the angle of incidence is equal to angle of reflection.

Explanation:- because we know, the wavelength of red colour is the maximum, then comes yellow, and then Violet.

The image has the dimensions as the object and is the same distance behind the mirror as the object is in front of the mirror. 
In the case, the object A is placed at a distance d in front of a plane mirror and the person stands right behind the object and the total distance between the person and the mirror is S. This is inclusive of the distance of the object from the mirror. 
Therefore, the distance of the image from the individual to the image that is formed at a distance d on the other side is given as 
S+d.

Let, the angle of inclination be Theta ° Since the formula is 360 / theta - 1
Mirrors are inclined at an angle of 60°
360/60 - 1 = 5
Therefore, the number of images formed is 5.

The minimum heights needed for this purpose is 10/3m.

Given, no. of images = 5 
We know, 
No. Of images = 360/ theta  - 1 
=>  5 = 360/ theta - 1 
=>  6 = 360/theta 
=> theta = 360/6
=> angle = 60° 

In the case of multiple images formed by a thick plane mirror, the brightest image is typically the first image. This is because the first image is formed directly by the reflection from the front surface of the mirror, where the most amount of light is reflected. Subsequent images are formed due to multiple reflections between the front and back surfaces of the mirror, which involve more loss of light and thus appear dimmer.

So, the correct answer is 2) first.

Correct Answer :- C

Explanation:- Concave mirrors can form inverted and real images and also virtual and erect images. Size can be smaller, larger or of the same size depending on the position of the object. Smaller than the size of the object, always.

If the mirror is a convex mirror, your image (actual size) will be smaller than you are. If the mirror is a concave mirror, your image (actual size) will usually be bigger than you are, depending on your distance from the mirror.

Here, f = -10 cmcm
m = -5 ( image is 5 times larger than the object) 
⇒ -v/ u = -5
⇒ v = 5u 
By using mirror formula, 
1/f  = 1/u + 1/v 
⇒ 1/-10   =  1/u +1/5u 
⇒ 1/-10  = 6/5u 
⇒ 5u  = 6*(-10) cm 
⇒ u =   -60/5 cm
⇒ u  =  -12 cm 
So, the distance of object is 12 cm from the mirror. 

Given, f = 20 cm, h1 = 2h0 

⇒ h1/ho = m = 2 

v / u = 2 => v = 2u

1/ v - 1/ u = 1/ f ( lens formula) 

⇒  1/2u - 1/-u  = 1/ 20 

⇒ 3/ 2u = 1/ 20

⇒ u = 30 cm 

So, option ( c) is the correct answer.

If  refractive index of glass w.r.t air is 3/2 , then  refractive index of air w. r. t glass will be it's reciprocal ie. ⅔ ..

We have, ( 1.5-1) *90 
=  0.5 *90 ⇒ 45° 
Now, 45-30+90° 
⇒  105° 
Angle of emergence has inclination with second surface. 
⇒ 90 - 105 
⇒ -15 
This shows that light ray will not emerge out of the prism. 

When the monochromatic light passes from vacuum to medium there is no difference in frequency. Because whichever medium light enters there is no change in its frequency change in medium leads to change in velocity. 

If the glass and the liquid are having same refractive index then glass won't be  visible as it refracts light at same angle as the liquid does so that is reason that a glass piece is not visible in the liquid.

Refractive index of water :- 
Speed of light in vacuum / speed of light in water
4/3 = (3*10⁸) /x 
x  = 2.25 * 10⁸ m/s

Refractive index of water, nw =  4/3
Refractive index  of  glass, ng =  3/2 
Refractive index of water w. r. t glass
 n_gw = 4/3 / 3/2   =>  8/9