Light Reflection and Refraction Class 10 Science Important Questions

Important Questions Class 10

Please refer to Chapter 10 Light Reflection and Refraction Class 10 Science Important Questions with solutions provided below. These questions and answers have been provided for Class 10 Science based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 10 Science for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 10.

Class 10 Science Important Questions Light Reflection and Refraction Chapter 10

Very Short Answer:

Question: What is the magnification of the images formed by plane mirrors and why?
Answer: Magnification of images formed by plane mirrors is unity because for plane mirrors, the size of the image formed is equal to that of the object.

Question: What is the nature of the image formed by a concave mirror if the magnification produced by the mirror is +3?
Answer: Since, the sign of given magnification of the image is positive (+ ve) and greater than one so the image formed is virtual, erect and enlarged.

Question: What kind of mirrors are used in big shopping stores to watch activities of customers?
Answer: Convex mirrors are used in big shopping stores to watch activities of customers.

Question: Explain why a ray of light passing through the centre of curvature of a concave mirror gets reflected along the same path.
Answer: A ray passing through centre of curvature of a concave mirror gets reflected along the same path because it acts as a normal to the surface of mirror, and we know that any ray pas passing through normal reflects along the same path.

Question: Copy this figure in your answer-book and show the direction of the light ray afer refiection.
Answer: The incident ray passing through focus, goes parallel to the principal axis afer the refiection through the given mirror.

Question: Draw the following diagram in your answer book and show the formation of image of the object AB with the help of suitable rays.

Light Reflection and Refraction Class 10 Science Important Questions

Answer: Image formed by an object when it is kept between the pole and the focus of a concave mirror is

Light Reflection and Refraction Class 10 Science Important Questions

Question: Draw the following diagram in your answer book and show the formation of image of the object AB with the help of suitable rays. 

Light Reflection and Refraction Class 10 Science Important Questions

Answer: In the given diagram, object is placed between centre of curvature (C) and focus (F). Image of the object AB can be obtained as follows: 

Light Reflection and Refraction Class 10 Science Important Questions

Question: Draw the following diagram in your answer book and show the formation of image with the help of suitable rays. 

Answer: In the given diagrams object is placed at centre of curvature of a concave mirror. Image formed by the object can be drawn as 

Light Reflection and Refraction Class 10 Science Important Questions

Question: What is meant by power of a lens?
Answer: Power is the degree of convergence or divergence of light rays achieved by a lens. It is defined as the reciprocal of its focal length. i.e., P=1/f

Short Answer: I

Question: State the two laws of reflection of light.
Answer: Laws of reflection of light states that (i) The angle of incidence is equal to the angle of reflection.
(ii) The incident ray, the reflected ray and the normal to the mirror at the point of incidence all lie in the same plane.

Question: An object is placed at a distance of 30 cm in front of a convex mirror of focal length 15 cm. Write four characteristics of the image formed by the mirror.
Answer: Four characteristics of the image formed by the given convex mirror of focal length 15 cm are :
(i) Virtual
(ii) Erect
(iii) Diminished
(iv) Image is always formed behind the mirror between pole and focus.

Question: List four characteristics of the images formed by plane mirrors.
Answer: Characteristics of the image formed by a plane mirror are 
(i) image distance is same as that of object distance
(ii) image formed is virtual and erect
(iii) image formed is of the same size as that of the object
(iv) image formed is laterally inverted (left appears right and right appears left).

Question: State any four characteristics of the image of an object formed by a plane mirror.
Answer: Characteristics of the image formed by a plane mirror are
(i) image distance is same as that of object distance
(ii) image formed is virtual and erect
(iii) image formed is of the same size as that of the object
(iv) image formed is laterally inverted (lft appears right and right appears left). 

Question: An object is placed at a distance of 12 cm in front of a concave mirror of radius of curvature 30 cm. List four characteristics of the image formed by the mirror.
Answer: Radius of curvature (R) = 30 cm, object distance is 12 cm in front of the mirror. Thus we can say that object is placed between focus and pole. Four characteristics of the image formed by the given concave mirror are :
(i) Virtual
(ii) Erect
(iii) Enlarged
(iv) Image is formed behind the mirror

Question: List two properties of the images formed by convex mirrors. Draw ray diagram in support of your answer. 
Answer: Convex mirrors always form diminished,virtual and erect images.
(a) Object placed at infinity 

Light Reflection and Refraction Class 10 Science Important Questions

(b) Object placed between innity and the pole P of the mirror 

Light Reflection and Refraction Class 10 Science Important Questions

Question: Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is achieved by this device.
Answer: Concave mirrors are used in the designing of solar furnaces. When a solar furnace is placed at the focus of a large concave mirror, it focuses a parallel beam of light on the furnace. Therefore, a high temperature is attained at the point after some time.

Question: “The magnification produced by a spherical mirror is –3”. List four informations you obtain from this statement about the mirror/image. 
Answer: Negative sign of magnification indicates that the image is real and inverted. Since the image is real and inverted, the mirror is concave and magnification of –3 indicates that the image is magnified.

Question: To construct a ray diagram we use two light rays which are so chosen that it is easy to know their directions aftr refraction from the lens. List these two rays and state the path of these rays afer refraction. Use these two rays to locate the image of an object placed between ‘f ’ and ‘2f ’ of a convex lens.
Answer: The two rays are : (i) A ray of light from the object, parallel to the principal axis, after refraction from a convex lens, passes through the principal focus on the other side of the lens and in case of concave lens, a ray appears to diverge from the principal focus located on the same side of the lens. 

Light Reflection and Refraction Class 10 Science Important Questions

(ii) A ray of light passing through the optical centre of a lens will emerge without any 
deviation. 

Light Reflection and Refraction Class 10 Science Important Questions

Question: Explain with the help of a diagram, why a pencil partly immersed in water appears to be bent at the water surface. 
Answer: This phenomenon is due to refraction of light at the interface of two media. Light rays coming from the immersed end C of the pencil bend away from the normal at the interface on reaching there as the rays are travelling from optically denser to a rarer medium. As shown in the diagram, when viewed from above, they appear to come from the point C’, slightly raised. This way, all the rays from the immersed portion of the pencil bend and as a result it appears to be raised. Hence the pencil appears to be bend at the interface. 

Light Reflection and Refraction Class 10 Science Important Questions

Question: An object is placed at a distance of 15 cm from a convex lens of focal length 20 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
Answer: Given : Object distance, u = – 15 cm Focal length, f = + 20 cm Using lens formula, As |u| < |f| The object is placed between F and optical centre of lens.
Thus, the four characteristics of the image formed by the convex lens are :
(i) Erect, (ii) Virtual, (iii) Enlarged image, (iv) Image is formed on the same side of the lens as the object.

Question: The refractive index of water is 1.33 and the speed of light in air is 3 × 108 m s–1. Calculate the speed of light in water. 
Answer:

Light Reflection and Refraction Class 10 Science Important Questions

Question: Draw ray diagram to represent the nature, position and relative size of the image formed by a convex lens for the object placed
(a) at 2F1 (b) between F1 and optical centre O of lens
Answer:  (a) Ray diagrams of an object placed at 2Finfront of convex lens can be drawn as follows:

Light Reflection and Refraction Class 10 Science Important Questions

(i) Thus image formed is real and inverted.
(ii) Image is formed at 2F2.
(iii) Image formed is of same size as that of the object.
(b) Ray diagrams of an object placed between Fand optical centre O of lens can be drawn as follows: 

Light Reflection and Refraction Class 10 Science Important Questions

(i) The image formed is virtual and erect.
(ii) Image is formed infront of the lens.
(iii) Image formed is enlarged

Question: The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should the position of the
object be relative to the mirror? Draw ray diagram to justify your answer. 
Answer: The position of the object should be between P and F

Light Reflection and Refraction Class 10 Science Important Questions

Question: The linear magnification produced by a spherical mirror is +1/3. Analysing this value state the (i) type of mirror and (ii) position
of the object with respect to the pole of the mirror. Draw any diagram to justify your answer. 
Answer: (i) Convex mirror
(ii) Between in innity and the pole of the mirror.

Light Reflection and Refraction Class 10 Science Important Questions

Question: What is the minimum number of raysrequired for locating the image formed by a concave mirror for an object? Draw a ray
diagram to show the formation of a virtual image by a concave mirror.
Answer: At least two rays are required for locating the image formed by a concave mirror for an object. Virtual image is formed when object is placed between pole and focus of concave mirror.

Light Reflection and Refraction Class 10 Science Important Questions

Short Answer: II

Question: The image of an object formed by a mirror is real, inverted and is of magnification –1. If the image is at a distance of 40 cm from the mirror, where is the object placed? Where would the image be if the object is moved 
Answer:
 Since the image formed by the mirror is real and inverted, therefore the mirror is concave and magnification of the mirror will be

Light Reflection and Refraction Class 10 Science Important Questions

i.e., object and image both are formed at the centre of curvature, i.e., 40 cm from the mirror. Now, if the object is moved 20 cm towards the mirror, the object will be at the focus of the mirror and therefore the image will be formed at infinity.

Question: An object 4 cm in height, is placed at 15 cm in front of a concave mirror of focal length 10 cm. At what distance from the mirror
should a screen be placed to obtain a sharp image of the object. Calculate the height of the image.
Answer: Given : object distance, u = –15 cm,
object height, h = 4 cm, focal length, f = –10 cm;
Image distance, v = ?
Using mirror formula,

Light Reflection and Refraction Class 10 Science Important Questions

In order to obtain a sharp image of the object on the screen, screen should be placed at a distance of 30 cm in front of the mirror.

Light Reflection and Refraction Class 10 Science Important Questions

Question: If the image formed by mirror for all positions of the object placed in front of it is always virtual and diminished, state the type of the mirror. Draw a ray diagram in support of your answer. Where are such mirrors commonly used and why?
Answer:
 If the image formed is always virtual and diminished then the mirror used is convex.

Light Reflection and Refraction Class 10 Science Important Questions

Convex mirrors are widely used as rear view mirrors in cars, motorcycles etc. It produces an erect image that is smaller in size than the object hence giving a wide view.

Question: The image of a candle flame placed at a distance of 30 cm from a mirror is formed on a screen placed in front of the mirror at a
distance of 60 cm from its pole. What is the nature of the mirror? Find its focal length. If the height of the flame is 2.4 cm, find the height of its image. State whether the image formed is erect or inverted.
Answer:

Light Reflection and Refraction Class 10 Science Important Questions

Question: To construct a ray diagram we use two rays of light which are so chosen that it is easy to determine their directions aftr reflection from the mirror. Choose these two rays and state the path of these rays aftr reflection from a concave mirror. Use these two rays tofind the nature and position of the image of an object placed at a distance of 15 cm from a concave mirror of focal length 10 cm. 
Answer: We use two rays of light, one passing through the centre of curvature of a concave mirror, and another is parallel to the principal axis. After rflection, the ray passing through the centre of a concave mirror is reflected back along the same path and the ray parallel to the principal axis will pass through the principal focus.
u = –15 cm, f = –10 cm

Light Reflection and Refraction Class 10 Science Important Questions

From ray diagram, v = –30 cm, i.e., beyond C
Nature of image is real, inverted and magnified. 

Question: Draw a ray diagram to show the path of the reflected ray in each of the following cases. A ray of light incident on a convex mirror :
(a) strikes at its pole making an angle θ from the principal axis.
(b) is directed towards its principle focus.
(c) is parallel to its principal axis.
Answer: 

Light Reflection and Refraction Class 10 Science Important Questions
Light Reflection and Refraction Class 10 Science Important Questions
Light Reflection and Refraction Class 10 Science Important Questions

Question: A spherical mirror produces an image of magnification –1 on a screen placed at a distance of 40 cm from the mirror.
(i) Write type of mirror.
(ii) What is the nature of the image formed?
(iii) How far is the object located from the mirror?
(iv) Draw the ray diagram to show the image formation in this case. 
Answer: (i) This is a concave mirror.
(ii) The image is real and inverted and of same size.
(iii) As m = – 1

Light Reflection and Refraction Class 10 Science Important Questions

Hence, object is located at centre of curvature i.e., at distance of 40 cm from the pole of the mirror.
(i) Concave mirror because the image is real,inverted.
(ii) Object is placed at C.

Light Reflection and Refraction Class 10 Science Important Questions

Question: If the image formed by a mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a ray diagram to justify your answer. Where and why do we generally use this type of mirror? 
Answer: If the image formed is always virtual and diminished then the mirror used is convex.

Light Reflection and Refraction Class 10 Science Important Questions

Convex mirrors are widely used as rear view mirrors in cars, motorcycles etc. It produces an
erect image that is smaller in size than the object hence giving a wide view.

Question: The image formed by a spherical mirror is real, inverted and its magnification is –2. If the image is at a distance of 30 cm from the mirror, where is the object placed? Find the focal length of the mirror. List two characteristics of the image formed if the object is moved 10 cm towards the mirror.
Answer: Since the image formed is real and inverted,the mirror is concave.

Light Reflection and Refraction Class 10 Science Important Questions

If the object is shifed 10 cm the mirror, then the object is between principal focus and the optical centre and the image formed will be virtual and
erect. 

Question: A spherical mirror produces an image of magnification –1.0 on a screen placed at a distance of 30 cm from the pole of the mirror.
(i) Write the type of mirror in this case.
(ii) What is the focal length of the mirror?
(iii) What is the nature of the images formed?
(iv) Draw the ray diagram to show the image formation in this case?
Answer: (i) The mirror is concave mirror.
(ii) Distance the image from the object = – 30 cm

Light Reflection and Refraction Class 10 Science Important Questions

(iii) Image formed is real and inverted and of the same size of the object.
(iv) (i) Concave mirror because the image is real, inverted.
(ii) Object is placed at C.

Light Reflection and Refraction Class 10 Science Important Questions

Question: A student wants to obtain an erect image of an object using a concave mirror of 12 cm focal length. What should be the range of distance of the candle flame from the mirror? State the nature and size of the image he is likely to observe. Draw a ray diagram to show the image formation in this case.
Answer: To obtain an erect image, the object is placedin between pole and the focus of the concave mirror. So range of distance of the candle flame from the mirror is in between 12 cm.
Nature of the image = Virtual and erect.
Size of the image = Enlarged   

Question: A student has a concave mirror of 20 cm focal length and he wants to see an erect image of his face in the mirror. What should be the range of distance of the mirror from his face? State the nature and size of the image he is likely to observe. Draw a ray diagram to justify your answer. 
Answer: Focal length of a concave mirror = 20 cm Range will be in between 20 cm. Nature of the image = Virtual and erect Size of the image = Enlarged

Light Reflection and Refraction Class 10 Science Important Questions

Question: Calculate the magnification of the image of an object placed perpendicular to the principal axis of a concave mirror of focal length 15 cm. The object is at a distance of 20 cm from the mirror.  
Answer:
 Given, focal length of concave mirror,

Light Reflection and Refraction Class 10 Science Important Questions

Question: Mention the types of mirrors used as (i) rear view mirrors, (ii) shaving mirrors. List two reasons to justify your answer in each case.
Answer: (i) Convex mirror is used as rear view mirror because
(a) it gives erect image.
(b) it gives diminished image thus provides wider view of traffc behind the vehicle.
(ii) Concave mirror is used as shaving mirror because
(a) it gives erect image when mirror is close to the face.
(b) it gives enlarged image of the face so that a person can shave safely.

Question: State the types of mirrors used for (i) headlights and (ii) rear view mirrors, in motorcycles. Give reason to justify your answer in each case. 
Answer: (i) Concave mirrors are used in headlights of cars to get powerful beams of light.
(ii) Convex mirrors are used as rear-view mirrors of vehicle to get a wider field of view and and erect image of traffc behind.

Question: An object is placed between infinity and the pole of a convex mirror. Draw a ray diagram and also state the position, the relative size and the nature of the image formed.
Answer:

Light Reflection and Refraction Class 10 Science Important Questions

Position : Image is formed between pole and principal focus of the mirror.
Relative size : Image formed is diminished. Nature : Image formed is virtual and erect.

Question: Draw ray diagrams to show the formation of three times magnified (a) real, and (b) virtual image of an object by a converging lens. Mark the positions of O, F and 2F in each diagram.
Answer: Ray diagrams of an object placed between F1 and optical centre O of lens can be drawn as follows:

Light Reflection and Refraction Class 10 Science Important Questions

(i) The image formed is virtual and erect.
(ii) Image is formed infront of the lens.
(iii) Image formed is enlarged.

Question: With the help of a ray diagram explain why a convex mirror is preferred for rear view mirrors in the motor cars.
Answer: Convex mirror is preferred for rear view mirrors in motor cars because no matter where the object is located infront of convex mirror, it always gives erect and diminished image of the object, so that driver is able to see the large traffic view in small area and the image is erect. This can be interpreted from the following diagram.

Light Reflection and Refraction Class 10 Science Important Questions

Question: (a) Draw a diagram to show the refraction of light through a glass slab and mark angle of refraction and the lateral shft suffered
by a ray of light while passing through the slab. 
(b) If the refractive index of glass for light going from air to glass is 3/2, find the refractive index of air for light going from glass to air. 

Answer: 

Light Reflection and Refraction Class 10 Science Important Questions


(b) Refractive index of glass w.r.t air is 

Question: The image of an object formed by a lens is of magnification –1. If the distance between the object and its image is 60 cm, what is the focal length of the lens? If the object is moved
Answer: Magnification of –1 indicates that the image is real and inverted and is of the same size as of the object. The object must be at 2f and image also at 2f on the other side.
Total distance between image and object Also 4f = 60 cm⇒ f = 15 cm If object is moved 20 cm towards the lens, then the object will be between focus and optical centre of the lens and image formed will be virtual and erect and on the same side of the lens

Light Reflection and Refraction Class 10 Science Important Questions

Long Answer:

Question: (a) If the image formed by a mirror for all positions of the object placed in front of it is always diminished, erect and virtual state the type of the mirror and also draw a ray diagram to justify your answer. Write one use such mirrors are put to and why?
(b) Define the radius of curvature of spherical mirrors. Find the nature and focal length of a spherical mirror whose radius of curvature is +24 cm.
Answer: (a) If the image formed by a mirror for all positions of the object placed in front of it is always diminished, erect and virtual then the mirror is convex mirror.
The ray diagrams for the formation of image by a convex mirror for the rst position when the object is at in finity and the second position when the object is at a finite distance from the mirror is shown

Light Reflection and Refraction Class 10 Science Important Questions

Uses of Convex Mirrors Convex mirrors are commonly used as rear-view (wing) mirrors in vehicles because they always give an erect, though diminished, image. Also, they have a wider field of view as they are curved outwards. Thus, convex mirrors enable the driver to view a large area.
(b) Radius of Curvature : The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the radius of curvature of the mirror. It is represented by the letter R. 
∴ The radius of curvature is equal to twice the focal length.
∴ R = 2f
If R = +24 cm ∴ f = R/2=24/2=12 cm
Since the radius of curvature is positive. Then the mirror is convex mirror. Hence the nature of the image is virtual and erect.

Question: It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.
(i) What should be the range of distance of a object placed in front of the mirror?
(ii) Will the image be smaller or larger than the object. Draw ray diagram to show the formation of image in this case.
(iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror?
Draw ray diagram for this situation also to justify your answer.
Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams. 
Answer: Given : focal length of the concave mirror f = 12 cm
(i) If the object is placed between the pole and focus of the concave mirror, then the image formed is virtual and erect. Therefore, the range of distance of the object should be 0 < u < 12 cm. 
(ii)The image formed will be enlarged as shown below.

Light Reflection and Refraction Class 10 Science Important Questions

  
(iii) If the object is placed 24 cm in front of the mirror i.e., at the centre of the curvature then the image will also be formed at the centre of the curvature.

Light Reflection and Refraction Class 10 Science Important Questions

Question: (a) To construct a ray diagram we use two rays which are so chosen that it is easy to know their directions afer reflection from the mirror. Use these two rays and draw ray diagram to locate the image of an object placed between pole and focus of a concave mirror.
(b) A concave mirror produces three times magnified image on a screen. If the objects placed 20 cm in front of the mirror, how far is the screen from the object?
Answer: (a) Two lights rays whose path of reflection are priorly known are :
(i) When the incident ray passes through the centre of curvature of a concave mirror, it gets reflected in the same path.
(ii) When the ray is incident obliquely to the principal axis, towards the pole of mirror, it gets reflected back by making equal angles with the principal axis (laws of reflections).
Suppose an object is placed between focus and pole of the concave mirror. Then by using the above two rays, the image of the object can belocated as

Light Reflection and Refraction Class 10 Science Important Questions

Image formed is virtual, erect, magnified and it is formed behind the mirror.
(b) Given : Magnification, m = – 3 Object-distance, u = – 20 cm
Magnification, m=- v/u or -3= -v/-20 or v=-60 cm
The screen is placed in front of the mirror at a distance of 60 cm from the pole.
Thus, the screen is placed (= 60 cm – 20 cm) 40 cm away from the object.

Question: Suppose you have three concave mirrors A, B and C of focal lengths 10 cm, 15 cm and 20 cm. For each concave mirror you perform the experiment of image formation for three values of object distances of 10 cm, 20 cm and 30 cm. By giving reason, answer the following:
(a) For the three object distances, identify the mirror/mirrors which will form an image of magnification –1.
(b) Out of the three mirrors, identify the mirror which would be preferred to be used for shaving purposes/make up.
(c) For the mirror B draw ray diagram for image formation for object distances 10 cm and 20 cm. 
Answer: Given : fa = 10 cm, fb = 15 cm, fc = 20 cm
ua = 10 cm, ub = 20 cm, uc = 30 cm
(a) Magnfication of –1 implies that size of image is same as that of object or image is formed at the same distance as of the object. is is the case when
the object distance, u = 2f, i.e., when the object is at the centre of the curvature.
For fa , ub and for fb, uc , we get magnication – 1.
(b) Concave mirror forms virtual, erect and magnied image when the object is between focus and pole of the mirror, i.e., direct distance should
be less than the focal length of the mirror.
For object distance 10 cm, mirrors of focal length fb = 15 cm and fc = 20 cm can be used.
(c) 

Light Reflection and Refraction Class 10 Science Important Questions

Question: (a) Define the following terms in the context of spherical mirrors:
(i) Pole
(ii) Centre of curvature
(iii) Principal axis
(iv) Principal focus
(b) Draw ray diagrams to show the principal focus of a
(i) Concave mirror
(ii) Convex mirror
(c) Consider the following diagram in which
M is a mirror and P is an object and Q is its magnified image formed by the mirror.

Light Reflection and Refraction Class 10 Science Important Questions

State the type of the mirror M and one characteristic property of the image Q
Answer: (a) (i) Pole : The centre of the reflecting surface of a spherical mirror is a point called the pole. It lies in the surface of the mirror and its represented by the letter P.
(ii) Centre of curvature : The reflecting surface of a spherical mirror is a part of a sphere which has acentre. is point is called the centre of curvature of spherical mirror and is represented by the letter C. 
(iii) Principal axis : An imaginary line passing through the pole and the centre of curvature of a spherical mirror and normal to the mirror at its pole is called principal axis.
(iv) Principal focus : Incident rays parallel to principal axis, after reflection either converge to as appear to diverge from a fixed point on the principal axis known as principal focus of the spherical mirror.
(b) (i) 

Light Reflection and Refraction Class 10 Science Important Questions

(c) The object is placed between focus and pole of the mirror and a magnied image is formed behind the mirror.
∴ The mirror is concave and image formed is virtual and erect.

Question: A student has focused the image of a candle flame on a white screen using a concave mirror. The situation is a given below :
Length of the flame = 1.5 cm
Focal length of the mirror = 12 cm
Distance of flame from the mirror = 18 cm
If the flame is perpendicular to the principal axis of the mirror, then calculate the following:
(a) Distance of the image from the mirror
(b) Length of the image If the distance between the mirror and the flame is reduced to 10 cm, then what would be observed on the screen? Draw ray diagram to justify your answer from this situation.
Answer: Given: focal length of the concave mirror,
f = – 12 cm
Length of the flame, h = 1.5 cm
Distance of flame from the mirror, u = –18 cm 

Light Reflection and Refraction Class 10 Science Important Questions

Question: A student wants to project the image of a candle flame on the walls of school laboratory by using a mirror.
(a) Which type of mirror should he use and why?
(b) At what distance in terms of focal length ‘f ’ of the mirror should he place the candle flame so as to get the magnified image on the wall?
(c) Draw a ray diagram to show the formation of image in this case.
(d) Can he use this mirror to project a diminished image of the candle flame on the same wall? State ‘how’ if your answer is ‘yes’ and ‘why not’ if your answer is ‘no’
Answer: (a) He should use concave mirror to get image of candle flame on the walls of school laboratory.
Because concave mirror is a converging mirror and produce real image.
(b) He should place the candleflame in between centre of curvature C and principal focus F of the mirror to get the magnied image on the wall.
(c) 

Light Reflection and Refraction Class 10 Science Important Questions

(d) Yes, he can use concave mirror to project a diminished image of the candle flame on the same wall. He has to place the candle flame beyond centre of curvature to get diminished image.

Question: Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follows,without doing any calculations :

Light Reflection and Refraction Class 10 Science Important Questions

Answer: (a) When an object placed at the 2F from a convex lens, then its image is formed on the other side of the lens at the same distance from the lens.
Thus from S.No.(3) we can say that.
∴ f = v / 2⇒ f = 30/2 = +15cm
Thus, the focal length is + 15 cm.
(b) In this case S.No. (6) is incorrect as the object distance is between focus and pole, for such case, the image formed is virtual and on the same side as the object, hence image distance is negative.
(c)The approximate value of magnification for object distance –20 cm and image distance + 60 cm is –3. 

Light Reflection and Refraction Class 10 Science Important Questions

Question: Analyse the following observation table showing variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations.

Light Reflection and Refraction Class 10 Science Important Questions

(a) What is the focal length of the convex lens? Give reason to justify your answer.
(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?
(c) Select an appropriate scale and draw a ray diagram for the observation at S. No. 2. Also find the approximate value of magnification. 
Answer: (a) When an object is placed at 2F from the convex lens, then its image is formed on the other side of the lens at the same distance from the lens.
Thus from S.No. (3), we can say that
∴ f = v/2 = 40/2=20 cm
(b) In this case, S.No. (6) is incorrect as the object distance is between focus and optical centre for such cases, the image formed is virtual and image
distance is negative 

Light Reflection and Refraction Class 10 Science Important Questions

The approximate value of magnification for object
distance –60 cm and image distance +30 cm is –1/2.

Question: List the sign conventions for reflection of light by spherical mirrors. Draw a diagram and apply these conventions in the determination of focal length of a spherical mirror which forms a three times magnified real image of an object placed 16 cm infront of it.
Answer: Sign Convention for Reflection by Spherical Mirrors : While dealing with the reflection of light by spherical mirrors, we shall follow a set of sign conventions called the New Cartesian Sign Convention. The conventions are as follows:
(i) The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.
(ii) All distances parallel to the principal axis are measured from the pole of the mirror.
(iii) All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.
(iv) Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive.
(v) Distances measured perpendicular to and below the principal axis (along-y-axis) are taken as negative.

Light Reflection and Refraction Class 10 Science Important Questions

Question: (a) Draw a ray diagram to show the formation of image by a concave lens when an object is placed in front of it.
(b) In the above diagram mark the object distance (u) and the image distance (v) with their proper sign (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length ( f ) of the concave lens in this case.
(c) Find the nature and power of a lens which forms a real and inverted image of magnification –1 at a distance of 40 cm from its optical centre.
Answer:

Light Reflection and Refraction Class 10 Science Important Questions

Question: (a) Define focal length of a divergent lens.
(b) A divergent lens has a focal length of 30 cm forms the image of an object of size 6 cm on the same side as the object at a distance of 15 cm from its optical centre. Use lens formula to determine the distance of the object from the lens and the size of the image formed.
(c) Draw a ray diagram to show the formation of image in the above situation.
Answer: (a) Distance between the principal focus and the optical centre is known as the focal length of the lens.
(b) Given, f = –30 cm, v = –15 cm, h = 6 cm Now, from lens formula,

Light Reflection and Refraction Class 10 Science Important Questions

Question: At what distance from a concave lens of focal length 20 cm a 6 cm tall object be placed so as to obtain its image at 15 cm from the lens?
Also calculate the size of the image formed. Draw a ray diagram to justify your answer for the above situation and label it.
Answer: Focal length of concave lens, f = –20 cm Height of the object, h = 6 cm Image distance, v = –15 cm From lens formula, 

Light Reflection and Refraction Class 10 Science Important Questions

Question: (a) Draw a ray diagram to show the formation of image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.
(b) In the above ray diagram mark the object distance (u) and the image distance (v) with their proper sign (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.
(c) Find the power of a convex lens which forms a real and inverted image of magnification –1 of an object placed at a distance of 20 cm from its optical centre.
Answer: (a) Draw a ray diagram to show the formation of image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.
(b) In the above ray diagram mark the object distance (u) and the image distance (v) with their proper sign (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens inthis case.
(c) Find the power of a convex lens which forms a real and inverted image of magnification –1 of an object placed at a distance of 20 cm from its optical centre.

Light Reflection and Refraction Class 10 Science Important Questions