LIGHT, Class X Physics case study Light Reflection and Refraction Question

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Class X Physics case study Light Reflection and Refraction Question

Q 1: Read the following and answer any four questions from (i) to (v).
The spherical mirror forms different types of images when the object is placed at different locations. When the image is formed on screen, the image is real and when the image does not form on screen, the image is virtual. When the two reflected rays meet actually, the image is real and when they appear to meet, the image is virtual. A concave mirror always forms a real and inverted image for different positions of the object. But if the object is placed between the focus and pole. the image formed is virtual and erect. A convex mirror always forms a virtual, erect, and diminished image. A concave mirror is used as a doctor’s head mirror to focus light on body parts like eyes, ears, nose, etc., to be examined because it can form erect and magnified images of the object. The convex mirror is used as a rearview mirror in automobiles because it can form a small and erect image of an object.

(i) When an object is placed at the centre of curvature of a concave mirror, the image formed is

(a) larger than the object                         

(b) smaller than the object                      

(c) the same size as that of the object           

(d) the highly enlarged                     

Answer:(c)

(ii) No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be                                                                                

(a) plane                                                      

(b) concave                                           

(c) convex                                                    

(d) either plane or convex.                  

Answer: (d)                                                                                               

(iii) A child is standing in front of a magic mirror. She finds the image of her head bigger, the middle portion of her body of the same size, and that of the legs smaller. The following is the order of combinations for the magic mirror from the top.       

(a) Plane, convex, and concave                    

(b) Convex, concave, and plane       

(c) Concave, plane, and convex                    

(d) Convex, plane, and concave     

Answer: (c)                                                                                            

(iv) To get an image larger than the object, one can use

(a) convex mirror but not a concave mirror

(b) a concave mirror but not a convex mirror

(c) either a convex mirror or a concave mirror

(d) a plane mirror.                                                                             

Answer: (b)                                                                                          

(v) A convex mirror has wider field of view because                                

(a) the image formed is much smaller than the object and a large number of images can be seen.                                                                               

(b) the image formed is much closer to the mirror                               

(c) both (a) and (b)                                                                                  

(d) none of these.                                                                                 

Answer: (c)

Q 2: Read the following and answer any four questions from (i) to (v).

The lenses form different types of images when objects are placed at different locations. When a ray is incident parallel to the principal axis, then after refraction, it passes through the focus or appears to come from the focus. When a ray goes through the optical centre of the lens, it passes without any deviation. If the object is placed between the focus and the optical center of the convex lens, an erect and magnified image is formed. As the object is brought closer to the convex lens from infinity to focus, the image moves away from the convex lens from focus to infinity. Also, the size of the image goes on increasing and the image is always real and inverted. A concave lens always gives a virtual, erect, and diminished image irrespective of the position of the object.                                                         

(i) The location of the image formed by a convex lens when the object is placed at infinity is                                                                              

(a) at Focus                                                            

(b) at 2F                                        

(c) at the optical center                                        

(d) between Fand 2F                   

Answer: (a)                                                                                            

(ii) When the object is placed at the focus of the concave lens, the image formed is  

(a) real and smaller                                             

(b) virtual and inverted                

(c) virtual and smaller                                         

(d) real and erect            

Answer: (b)                                                                              

(iii) The size of the image formed by a convex lens when the object is placed at the focus of a convex lens is                                                            

(a) small                                                              

(b) point in size                              

(c) highly magnified                                           

(d) same as that of the object       

Answer: (c)                                                                                        

(iv) When the object is placed at 2F in front of a convex lens, the location of the image is                                                                                               

(a) at F                                                         

(b) at 2 F on the other side                 

(c) at infinity                                               

(d) between F and the optical center  

Answer: (b)                                                                                                  

(v) At which location of the object in front of the concave lens, the image between the focus and optical center is formed

(a) anywhere between centre and infinity                                            

(b) at F                                                                                                         

(c) at 2F                                                                                                

(d) infinity                                                                                         

Answer: (a)

Question3. The light path is deviated when the ray of light travels from one transparent medium to another. This phenomenon is called refraction of light. The bending of light depends on the optical density of the medium through which the light passes.


The speed of light varies from medium to medium. A medium in which the speed of light is more is an optically rarer medium whereas in which the speed of light is less is an optically denser medium. Whenever light goes from one medium to another, the frequency of light does not change however, speed and wavelength change. It concluded that change in the speed of light is the basic cause of refraction.

(i) When light travels from air to glass, the ray of  light bends                   

(a)  toward the normal                                                                              

(b) away from normal                                                                    

(c) anywhere                                                                             

(d) none of these.                                                                             

Answer. (a)

(ii) A ray of light passes from a medium A to another medium B. No bending of light occurs if light if the ray of light hits the boundary of medium B at an angle of                                                                  

(a) 00                                                                                                         

(b) 450                                                                                                    

(c) 900                                                                                                                           

(d) 1200                                                                                                  

Answer. (c)

(iii) When light passes from one medium to another, the frequency of light. 

(a) increase                                                                                      

(b) decrease                                                                          

(c) remains same                                                                    

(d) none of these.                                                                                 

Answer. (c)

(iv)  When light passes from glass to water, the speed of light      

(a) increase                                                                                  

(b) decrease                                                                           

(c) remains same                                         

(d) first increases then decreases.                                                   

Answer. (a)

(v) The bottom of a pool filled with water appears to be _______ due to the retraction of light.                  

(a) shallower                                                                                    

(b) deeper                                                                           

(c) at the same depth                                                                      

(d) empty.                                                                                                

Answer. (a)

Question 4. The refraction of light on going from one medium to another takes place according to two laws which are known as the laws of refraction of light. These laws are
                                                                                          
1. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is always constant for the pair of media in contact.

The constant is called the refractive index of the second medium with respect to the first medium. The refractive index is also defined as the ratio of the speed of light in a vacuum to the speed of light in the medium.

 2. the incident ray,  refractive ray, and normal all lie in the same plane. This law is called Snell's law of refraction.

(i) when light travels from air to glass. glass.

(a) angle of incidence > angle of refraction                                      

(b) angle of incidence < angle of refraction                                       

(c) angle of incidence = angle of refraction                             

(d) can’t say                                                                                       

Answer. (a)

(ii) when light travels from air to medium, the angle of incidence is 450 and the angle of refraction is 300. The refractive index of the second medium with respect to the first medium is                                    

(a) 1.41                                                                                                    

(b) 1.50                                                                                                             

(c) 1.23                                                                                                        

(d) 1                                                                                                          

Answer. (a)

(iii) In which medium, the speed of light is minimum?                                

(a) Air

(b) Glass

(c) Water

(d) Diamond.                                                                                       

Answer. (d)

(iv) If the refractive index of glass is 1.5 and the speed of light in air is 3 × 108  m/s the speed of light in glass is   

(a) 2 × 108  m/s

(b) 2.9 × 108  m/s

(c) 4.5 × 108  m/s

(d) 3 × 108  m/s                                                                                     

Answer. (a)

(v) Refractive index of a with respect to b is 2. Find the refractive index of b with respect to a.

(a) 0.4

(b) 0.5

(c) 0.25

(d) 2.                                                                                              

Answer. (b)

Question 5.  A Lens is a piece of transparent material bounded by two curved surfaces. There are two types of lenses convex lens and concave lens.

Convex lens is made up of a transparent medium bounded by two spherical surfaces such that it is thicker at the middle and thinner at the edge. A concave lens is also made up of a transparent medium that is thicker at the edge and thinner at the middle. The midpoint of the lens is called the optical centre.

A point on the principal axis, where the incident parallel rays meet or appear to come out after refraction is called focus.
A Convex lens converges a parallel beam of light to the other side whereas a concave lens spreads out.

(i) Which of the following lenses would you prefer to use while reading small letters found in a dictionary?            

(a) A convex lens of focal length 50 cm.

(b) A concave lens of focal length 50 cm.

(c) A convex lens of focal length 5 cm.

(d) A concave lens of focal length 5 cm.                         

Answer. (c)

(ii) Which type of lenses are shown in given figures (i) and (ii).


                  
(a) Plano concave, concavo convex

(b) Plano-convex, convexo concave

(c) Double concave, concave-convex

(d) Convexo concave, double convex.                                      

Answer. (a)

(iii) A small bulb is placed at the focal point of a converging lens. When the bulb is switched on, the lens produces

(a) a convergent beam of light

(b) a divergent beam of light

(c) a parallel beam of light

(d) a patch of coloured light.                                                             

Answer. (c)

(iv) The part of lens through which the refraction takes place is called

(a) aperture

(b) centre of curvature   

(c) principal axis 

(d) focus .                                    

Answer. (a)

(v) A water drop acts as a

(a) convex lens 

(b) concave lens

(c) double concave lens

(d)  none of these.                                                                     

Answer. (a)

Question 6. The relationship between the distance of the object from the lens (u), the distance of the image from the lens (v), and the focal length (f) of the lens is called the lens formula. It can be written as

 1/f = 1/v-1/u   

The size of the image formed by a lens depends on the position of the object from the lens. A lens of a short focal length has more power whereas a lens of a long focal length has less power. When the lens is convex, the power is positive and for a concave lens, the power is negative. The magnification produced by a lens is the ratio of the height of the image to the height of the object as the size of the image relative to the object is given by linear magnification (m).
When m is negative, the image formed is real and when m is positive, the image formed is virtual. If m < 1, the size of the image is smaller than the object. If m > 1, the size of the image is larger than the object.

(i) An object 4 cm in height is placed at a distance of 10 cm from a convex lens of focal length 20 cm. The position of image is

(a) – 20 cm

(b) 20 cm

(c) – 10 cm

(d) 10 cm.                                                                                             

Answer. (a)

(ii) In the above question, the size of image is

(a) 16 cm

(b) 8 cm

(c) 4 cm

(d) 2 cm.                                                                      

Answer. (b)

(iii) An object is placed 50 cm from a concave lens and produces a virtual image at a distance of 10 cm infront of lens. The focal length of lens is

(a) – 25 cm

(b) – 12.5 cm

(c) 12.5 cm

(d) 10 cm. 

Answer. (c)                                                                                              

(iv) A convex lens forms an image of magnification -2 of the height of the image is 6 cm,

(a) 6 cm

(b) 4 cm

(c) 3 cm  

(d) 2 cm.                                                                                                         

Answer. (b)

(v) A concave lens of focal length 5 cm, the power of the lens is

(a) 20 D 

(b) - 20 D

(c) 90 D

(d) - 5 D.                                                                                             

Answer. (a)

Question 7. The lenses form different types of images when objects are at different locations. When a ray is incident parallel to the principal axis, then after refraction, it passes through the focus or appears to come from the focus. When a ray goes through the optical centre of the lens, it passes without any deviation.                                                                                             

If the object is placed between focus and optical centre of the convex lens, erect and magnified image is formed. As the object is brought closer to the convex lens from infinity to focus, the image move away from the convex lens from focus to infinity. Also the size of image goes on increasing and the image is always real and inverted. A concave lens always gives a virtual, erect, and diminished image irrespective to the position of the object. 

(i) The location of image by a convex lens when the object is placed at infinity is

(a) at focus

(b) at 2f

(c) at optical centre

(d) between F and 2F.                                                                      

Answer. (a)

(ii) When the object is placed at the focus of concave lens, the image formed is

(a) real and smaller

(b) virtual and inverted

(c) virtual and smaller

(d) real and erect.                                                                             

Answer. (b)

(iii) The size of the image formed by a convex lens when the object is placed at the focus of a convex lens is

(a) small

(b) a point in size

(c) highly magnified    

(d) the same as that of an object.                                                    

Answer. (b)

(iv) When the object is placed at 2F in front of a convex lens, the location of the image is

(a) at F

(b) at 2 F on the other side

(c) at infinity

(d) between F and the optical centre.   

Answer. (c)

(v) At which location of the object in front of the concave lens, the image between the focus and optical centre is formed

(a) anywhere between the centre and infinity

(b) at F

(c) at 2F

(d) infinity.                                                                                      

Answer. (b)

 


  

                     


                                                                                        

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