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’. 

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

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

​​​​​​Option D: "A concave mirror can never form a diminished virtual image."

Correct. A concave mirror can form a diminished real image but never a diminished virtual image. Virtual images formed by concave mirrors are always enlarged.

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.

- The angle of incidence is the angle between the incoming ray and the normal (a line perpendicular to the surface).
- According to the law of reflection, the angle of incidence is equal to the angle of reflection.
- Given that the angle of incidence is 30 degrees, the angle of reflection will also be 30 degrees.
- Therefore, the correct answer is B: 30 degrees.

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. 

- The correct answer is B: The angle of incidence is always equal to the angle of reflection.
- This principle is known as the Law of Reflection.
- When light hits a smooth surface, it reflects in such a way that:
- The angle at which the light ray hits the surface (angle of incidence) is equal to the angle at which it leaves (angle of reflection).
- These angles are measured from the normal, an imaginary line perpendicular to the surface at the point of incidence.

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 ..

Reason:
For total internal reflection to occur:

1. Light must pass from a denser to a rarer medium (Condition I).
2. The angle of incidence must be greater than the critical angle (Condition III).

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

Analysis of the Options:

1. I. Convex Lens:

   • A convex lens can form a virtual image when the object is placed between the lens and its focal point. The image is virtual, erect, and magnified.
   • Correct.

2. II. Concave Lens:

   • A concave lens always forms a virtual, erect, and diminished image regardless of the object's position.
   • Correct.

3. III. Concave Mirror:

   • A concave mirror forms a virtual image when the object is placed between the pole and the focal point. The image is virtual, erect, and magnified.
   • Correct.