Chapter-10 The light – Reflection and Refraction NCERT Exemplar

1. Describe a concave mirror's primary emphasis.

Explanation:

After reflecting from a concave mirror, light rays that are parallel to that mirror's main axis converge at a particular spot on that axis. The main focus of the concave mirror is where this point is located.


2. Focus serial mirror has a radius of curvature of 20 centimeters. How long is its main point?

Explanation:

20 centimeters is the radius of curvature (R).

Focal length equals 2  Radius of Curvature of the Spherical Mirror (f)

R = 2f

f= R/2 = 20 / 2 = 10

Consequently, the spherical mirror's focal length is 10 centimeters.


3. The mirror that can produce an upright, magnified image of an item is to be named.

Explanation:

A concave mirror is the type of mirror that can produce an upright, enlarged image of an item.


4. Why do we favour convex mirrors over flat ones for rear-view mirrors in cars?

Explanation:

In cars and other vehicles, a convex mirror is favoured for the rear-view mirror because it provides a wider field of vision, allowing the driver to see the majority of the traffic behind him. When objects are put in front of convex mirrors, they always appear erect, virtual, and diminished.


5. mirrorsx mirror with a 32 centimeter radius of curvature should have a focal length of.

Explanation:

Curvature radius (R) equals 32 centimetres

Radius of Curvature equals 2  Focal Length (f)

R= 2f

f = R/2 = 32/2 = 16

The provided convex mirror's focal length is 16 cm as a result.


6.  A light beam moving through air strikes water at an angle. Does the light beam slant in the direction of the normal or away from it? Why?

Explanation:

The light beam deviates from its usual path. When a light beam transitions from an optically rarer (low refractive index) medium to an optically denser (high refractive index) medium, its speed decreases and it bends towards the normal. Since water is optically denser than air, a light ray hitting water from the outside will bend in the direction of normal.


7. Air-borne light with a refractive index of 1.50 penetrates glass. How fast is light moving through the glass? Light travels at a pace of 3 x 108 in a vacuum is 3 x 108 ms-1

Explanation:

Speed of light in vacuum divided by speed of light in medium gives the refractive index of a medium (nm).

The vacuum-bound speed of light (c) is 3  108 m/s.

Glass has a refractive index of 1.50 (ng).

Speed of light in glass (v) = Vacuum speed of light/Glass refractive factor

= c/ng

=3 × 108/1.50 = 2x 108 ms-1.


8. 2.4 is the refractive number of a diamond. How should this remark be interpreted?

Explanation:

The speed of light will slow down by a ratio of 2.42 in a diamond compared to its speed in the air because of the diamond's refractive index of 2.42.

Or to put it another way, the speed of light in a diamond is 1/2.42 times that of light in a vacuum.


9.  Describe one lens diopter of strength.

Explanation:

The symbol D stands for a diopter, which is the SI unit used to measure lens power. The strength of a lens with a 1-meter focal length is known as 1 diopter.


10.  Determine the strength of a 2 m concave lens.

Explanation:

The curved lens's focal length is 2 meters (f).

Lens power (P) equals 1/f = 1/(-2) = -0.5D.


11. Which of the materials listed below can't be used to create lenses?

(A) Water

(B) Glass 

© Plastic 

(D)  Clay

Explanation:

(D ) clay 

Explain:

Clay cannot be used to create lenses because light cannot pass through a lens made of clay.


12.  It is noted that the image created by a concave mirror is virtual, erect, and larger than the item. What should the object's location be?

  1. Between the main point of emphasis and the curve's center

  2.  In the middle of the curve

  3.  Outside of the curvature's middle

  4. In the space between the mirror's pole and its main centre.

Explanation:

(d) The item should be placed between the mirror's pole and its main focus.


13.  How should an item be positioned in front of a convex lens to obtain a true representation of the object’s size?

  1. At the lens’s primary focal

  2. At a focus length twice as long

  3. At infinite

  4. Between the lens’s optical centre and its main focal.

Explanation:

(b) You should position the item at twice the focal length.


14. The focal length of a spherical mirror and a thin spherical lens is -15 centimetres. The lens and the mirror are probably

  1. Both are curved.

  2. Both circular 

  3. The lens is convex and the reflection is concave.

  4. The lens is concave, but the reflection is convex.

Explanation:

The mirror are likely plane or convex.


15. Your reflection always looks upright no matter how far you are from the mirror. The glass is probably

  1. . A aircraft

  2. Concave 

  3. Convexity 

  4. either convex or flat

Explanation:

(Iv) The mirrors are most apt to be convex or plane.


16. Which of the following lenses would you choose to view small letters from a dictionary while wearing?

(a) A convex lens with a 50 centimeter focal length

(b) A concave lens with a 50 centimeter focal length

(c) A convex lens with a 5 centimeter focal length

(d) A concave lens with a 5 centimeter focal length

Explanation:

(c) When viewing tiny letters in a dictionary, a convex lens with a 5 cm focal length can be used.


17.  Using a concave mirror with a 15 cm focal length, we want to capture an upright picture of an object. What should the object's distance from the reflection fall within? What kind of picture is it? Does the picture outweigh or underweight the object? To illustrate the image creation in this scenario, create a ray diagram.

Explanation:

Range of the object's distance from the mirror's pole is 0 to 15 centimeters.

The image is erect, virtual, and bigger than the object.


18. Choose the appropriate kind of reflection for each of the instances below.

(a) A car's headlights

(b) A car's side- and rear-view mirrors

(c) Solar heater

Explanation:

Give a good explanation for your response.


19. Black paper covers one-half of a curved lens. Can I get a full picture of the object with this lens? Experiment to confirm your response. Describe what you noticed.

Explanation:

Yes, as depicted in the figure, it will result in a full image of the item. This can be demonstrated experimentally by looking at a screen image of a faraway object, like a tree, with the bottom half of the lens covered in black paper. However, the image’s brightness or strength will decrease.


20. A convex mirror with a 15 cm focal length is positioned 10 cm away from an object. Find the image’s location and type.

Explanation:

Convex mirror’s focal length (f) is +15 centimeters

Distance to object (u) = -10 centimeters

The mirror algorithm says that


21. A planar mirror magnifies objects by a factor of 1. Why does this matter?

Explanation:

The positive sign indicates that a plane mirror’s created virtual and erect since the magnification is , 1. The images side is identical to the objective size


22.  A convex mirror with a radius of curvature of 30 cm is positioned in front of a 5 cm object at a distance of 20 cm. Find the image's location, type, and size.

Explanation:

Distance to object (u) = -20 centimeters

Height of object (h) = 5 centimeters

30 centimeters is the radius of curvature (R).

Focal length equals 2  Radius of Curvature

R = 2f

f = 15 cm

The mirror algorithm says that


23. Determine a lens’s focal length with a power of -2.0 D. How does this optic work?

Explanation:

Lens strength (P) equals 1/f

P = -2D

F = -1/2 = -0.5 m

An adverse focus length is found in concave lenses. A curved lens is what it is as a result.


24. A +1.5 D corrective lens has been recommended by a physician. Determine the lens’s focal length. Converging or diverging is the recommended lens?

Explanation: 

Lens strength (P) equals 1/f

P = 1.5D

F = 1/1.5 = 10/15 = 0.66 m

With a positive focal length, a convex lens is used. In light of this, it is either a convex or a diverging lens.