Light Reflection and Refraction || Intext Question || CBSE Notes || Science 10

Light: Reflection and Refraction || Intext Question || CBSE/NCERT

Dear Students, Today we are going to share the Intext Question of Light- Reflection and Refraction. These question are very helpful for the students of 10th Class Students. These Intext Question is as per the latest syllabus of CBSE/State Board Examination.

Notes           Intext Question         Exercise Question  

Question 1:_ Define the principal focus of a concave mirror.

Answer: _ Light ray that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflection from the mirror. This point is known as principal focus of the concave mirror.

Question 2:_ The radius of curvature of a spherical mirror is 20 cm. What is its focus length?

Answer:_ Radius of curvature R = 20 cm

As we know that

Radius of curvature = 2 × Focal length

Hence, the focal length of the given spherical mirror is 10 cm.

Question 3:_ Name the mirror that can give an erect and enlarged image of an object.

Answer:_ Concave mirror produce an erect and enlarged image when the object is placed between its pole and principal focus.

Question 4:_ Why do we prefer a convex mirror as a rear view mirror in vehicles?

Answer:_ Concave mirror are prefer as a rear view mirror in vehicles because of the following reasons:

(1) Convex mirror produce an erect image of the object (traffic behind).

(2) Convex mirror give a wider field of view.

(3) The size of the image is much smaller than the size of the object which allows the driver to see most of the traffic behind him.

Question 5:_ Find the focal length of the convex mirror whose radius of curvature is 32cm.

Solution:_

Given Radius of curvature = +  32 cm (for convex mirror R is +ve)

Hence the focal length of the given convex mirror is 16 cm.

Question 6_ A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?

Answer: _ For real image m is taken as ─ ve

So, the image is formed at 30 cm on the same side of the mirror as that of an object.

Question 7_: A ray of light travelling in air enters obliquely into water.  Does the light ray bend toward normal or away from normal? Why?

Answer. The light ray bends toward normal.

When a ray of light travels from an optically rarer medium to an optically denser medium, its speed slow down and it bends towards normal. Since water is optical denser than air. Therefore a ray of light travelling from air into water will bends toward the normal.

Question 8:_ Light enters from air to glass having refractive index  1•50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 10⁸ m/s.

Answer: _ We know that the refractive index of the medium n_m is given 

Here, speed of light = 3 × 10⁸ m/s (given)

Refractive index = 1•50

Speed of light in glass

\ Speed of light in glass is 2 × 10⁸ m/s  

Question 9:_ Find out from table the medium having highest optical density. Also find the median with lowest optical density.

Material Medium	Refractive Index	Material Medium	Refractive Index
Air	1.003	Crown glass	1.52
Ice	1.31	Canada Balsam	1.53
Water	1.33	Rock Salt	1.54
Alcohol	1.36	Carbon Disulphate	1.63
Kerosene	1.44	Dense flint glass	1.65
Fused quartz	1.46	Ruby	1.71
Turpentine Oil	1.47	Sapphire	1.71
Benzene	1.50	Diamond	2.42

         

Answer:_ Optical density of a medium depends upon its refractive index. The higher the refractive index, higher the optical density and vice versa.

From the table it is appearant that diamond is having highest optical density (n = 2.42)) and air is having lowest optical density (n = 1.003).

Question 10:_ You are given kerosene, turpentine and water. In which of these does the light travels faster? Use the information given in the table.

Answer:_ Refractive index of kerosene, turpentine and water are 1.44, 1.47, 133 respectively.

As we know that the velocity of light in light in medium is inversely proportional to the refractive index of the medium.

Therefore, the light will travel faster in water having refractive index i.e. n = 1.33.

Question 11:_ The refractive index of diamond is a 2.42. What do you mean by this statement?

Answer:_ Refractive index show the comparison of light speed in two mediums.

Where C is the speed of light in air.

The refractive index of diamond is 2.42. this suggest that the speed of light in diamond will reduce by a factor 2.42 compared to the speed of light in air.

Question 12:_ Define 1 dioptre of Power.

Answer:_ Power of Lens is reciprocal of its focal length. if P is a power of lens of focal length F in metre then

The S.I unit of the power of lens is dioptre. It is denoted by D. 1 Dioptre  is defined as a power of lens of focal length 1 metre.

∴   D = 1 m^{─ 1} 

Question 13:_ A concave lens form a real and inverted image of a needle at a distance of 50 cm in front of it. Where is the needle placed in front of convex lens if the image is equal to the size of the object? Also find the power of the lens. 

Answer:_ When an object is placed at the centre of curvature 2F₁ of a convex lens, its image is formed at the centre of the curvature 2F₂ on the other side of the lens. The image formed is inverted and of the same size as the object, as shown in figure.

It is given that image of needle is formed at the distance of 50 cm from the convex lens.

Hence the needle is place in the front of the lens at a distance of 50 cm .

Object distance u = ─ 50 cm

Image distance v = 50 cm

Focal length = f

According to the lens formula

      ⟹ f = 25 cm = 0.25 m

 Hence the power of the given lens is + 4 D.

Question 14:_ Find the power of convex lens of the focal length 2 m.

Answer:_ Here given focal length f = ─2 m

 Here negative sign show the divergent nature of concave lens. Hence  the power of the given concave lens is ─ 0.5D  i.e. P = ─ 0.5 D