CLASS-10 SUBJECT : SCIENCE CHAPTER-10 LIGHT REFLECTION & REFRACTION.

 EVENTS CONVENT HIGH SCHOOL

09/11/2021      CLASS- 10   SESSION 2021-22
SUBJECT :  SCIENCE

CHAPTER-10
LIGHT REFLECTION & REFRACTION

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Question 1 Which one of the following materials cannot be used to make a lens ?
(a) Water
(b) Glass
(c) Plastic
(d) Clay
Answer:
(d) Clay

Question 2 The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object ?
(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus.
Answer:
(d) Between the pole of the mirror and its principal focus.

Question 3 Where should an object be placed in front of a convex lens to get a real image of the size of the object ?
(a) At the principal focus of the lens (b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus.
Answer:
(b) At twice the focal length.

Question 4 A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to be :
(a) Both concave.
(b) Both convex.
(c) the mirror is concave and the lens is convex.
(d) the mirror is convex, but the lens is concave.
Answer:
(a) Both concave

Question 5 No matter how far you stand from mirror, your image appears erect. The mirror is likely to be
(a) plane
(b) concave
(c) convex
(d) either plane or convex.
Answer:
(d) Either plane or convex.

Question 6 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) A convex lens of focal length 5 cm.

Question 7 We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror ? What is the nature of the image ? Is the image larger or smaller than the object ? Draw a ray diagram to show the image formation in this case.
Answer:
A concave mirror gives an erect image when the object is placed between the focus F and the pole P of the concave mirror, i.e., between 0 and 15 cm from the mirror. The image thus formed will be virtual, erect and larger than the object.

Question 8 Name the type of mirror used in the following situations.
(a) Headlights of a car.
(b) Side/rear-view mirror of a vehicle.
(c) Solar furnace.
Support your answer with reason.
Answer:
(a) Concave mirrors are used as reflectors in headlights of cars. When a bulb is located at the focus of the concave mirror, the light rays after reflection from the mirror travel over a large distance as a parallel beam of high intensity.

(b) A convex mirror is used as a side/rear-view mirror of a vehicle because

• A convex mirror always forms an erect, virtual and diminished image of an object placed anywhere in front it.
• A convex mirror has a wider field of view than a plane mirror of the same size.

(c) Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

Question 9 One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object ? Verify your answer experimentally. Explain your observations.
Answer:
A convex lens forms complete image of an object, even if its one half is covered with black paper. It can be explained by considering following two cases.
Case I : When the upper half of the lens is covered
In this case, a ray of light coming from the object will be refracted by the lower half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the following figure.

Case II: When the lower half of the lens Is covered
In this case, a ray of light coming from the object is refracted by the upper half of the lens. These rays meet at the other side of the lens to form the image of the given object, as shown in the given figure.

Question 10 An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
Answer:
Here : Object distance, u= -25 cm,
Object height, h = 5 cm,
Focal length, f = +10 cm
According to the lens formula, 1f=1ν−1u , we have
⇒ 1ν=1f−1u=110−125=15250orν=25015=16.66cm
The positive value of v shows that the image is formed at the other side of the lens.

The negative value of image height indicates that the image formed is inverted.
The position, size, and nature of image are shown alongside in the ray diagram.

Question 11
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens ? Draw the ray diagram.
Solution:
Focal length, f = -15 cm, Image distance, ν = -10 cm (as concave lens forms the image on the same side of the lens)
From the lens formula 1f=1ν−1u , we have

Object distance, u = -30 cm
The negative value of u indicates that the object is placed in front of the lens.

Question 12
An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.
Solution:
Object distance, u = -10 cm, Focal length, f = +15 cm, Image distance, ν = ?

Thus, image distance, ν = + 6 cm
Because ν is +ve, so a virtual image is formed at a distance of 6 cm behind the mirror.
Magnification, m=−υu=−6−30=15 (i.e. < 1)
The positive value of m shows that image erect and its value, which is less than 1, shows that image is smaller than the object. Thus, image is virtual, erect and diminished.

Class-8 Subject Science Chapter-16 LIGHTS

 EVENTS CONVENT HIGH SCHOOL

12/10/2021      CLASS-8     SESSION 2021-22
SUBJECT : SCIENCE

chapter - 16
lIGHTS 

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Textbook Questions

Question 1.Suppose you are in a dark room. Can you see objects in the room? Can you see objects out¬side the room? Explain.
Answer:
When we are in a dark room then we cannot see objects in the room. We can see the objects outside the room, because out of the room the light is available and the rays of light can enter our eyes after reflection from the objects.

Question 2.Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
Answer:

Regular Reflection	Diffused Reflection
(i) All the reflected rays are parallel.	(i) The reflected rays are not parallel.
(ii) It occurs on a smooth and polished surface.	(ii) It occurs on the rough surface.
(iii) Reflected rays are in one direction.	(iii) Reflected rays are scattered in different directions.

No, diffuse reflection doesn’t mean the failure of laws of reflection.

Question 3.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.

1. Polished wooden table
2. Chalk powder
3. Cardboard surface
4. Marble floor with water spread over it
5. Mirror
6. Piece of paper

Answer:

1. Regular reflection will take place because the surface is plane and polished.
2. Diffused reflection will take place because the surface is rough.
3. Diffused reflection will take place because the surface is rough.
4. Regular reflection will take place because the surface is smooth and plane.
5. Regular reflection will take place because the surface is plane and polished.
6. Diffused reflection will take place because the surface is rough.

Question 4.State the laws of reflection.
Answer:
The laws of reflections are:

• The incident ray, the normal and the reflected ray, all lie in the same plane.
• The angle of incidence is equal to the angle of reflection.

Question 5 Fill in the blanks in the following.
(a) A person 1 m in front of a plane mirror seems to be ______ m away from his image.
(b) If you touch your ______ ear with a right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with _____
(c) The size of the pupil becomes _______ when you see in dim light.
(d) Night birds have _______ cones than rods in their eyes.
Answer:
(a) 2
(b) left, left hand
(c) larger
(d) lesser

Question.6 Choose the correct option in Questions 
1.The angle of incidence is equal to the angle of reflection
(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never
Answer:
(a) Always

2. Image formed by a plane mirror is:
(a) virtual, behind the mirror and enlarged.
(b) virtual, behind the mirror and of the same size as the object.
(c) real at the surface of the mirror and enlarged.
(d) real, behind the mirror and of the same size as the object.
Answer:
(b) virtual, behind the mirror and of the same size as the object.

Class-6 Subject -Science Chapter-13 Fun with Magnets

 EVENTS CONVENT HIGH SCHOOL

12/10/2021      CLASS-6     SESSION 2021-22
SUBJECT : SCIENCE

chapter-13
FUN WITH MAGNETS 

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1. Fill in the blanks in the following:

(i) Artificial magnets are made in different shapes such as_________ ,_______ and
(ii) The materials which are attracted towards a magnet are called_________
(iii) Paper is not a________
(iv) In olden days, sailors used to find direction by suspending a piece of
(v) A magnet always has ________poles.
Ans:
(i) bar magnet, horse-shoe magnet and cylindrical magnet
(ii) magnetic materials
(iii) magnetic
(iv) bar magnet or lode stone
(v) two or a pair of

2. State whether the following statements are true or false:
(i) A cylindrical magnet has only one pole.
(ii) Natural magnets were discovered in Greece.
(iii) Similar poles of a magnet repel each other.
(iv) Maximum iron filings stick in the middle of a bar magnet when it is brought near them.
(v) Bar magnets always point towards North-South direction when suspended freely in air.
(vi) A compass can be used to find East-West direction at any place.
(vii) Rubber is a magnetic material.
Ans: 
(i) False
(ii) True
(iii) True
(iv) False
(v) True
(vi) True
(vii) False

3. It was observed that a pencil sharpener gets attracted by both the poles of a magnet although its body is made of plastic. Name a material that might have been used to make some part of it.
Ans:  Iron is used to make some part of sharpener due to which it is attracted toward magnet.

4.  Column I shows different positions in which one pole of a magnet is placed near that of the other. Column II indicates the resulting action between them for each situation. Fill in the blanks.

Ans:

VERY SHORT ANSWER TYPE QUESTIONS

1. Name the compound of iron contained in lode stone.
Ans: The compound of iron is iron oxide or magnetite.

2. Name the shepherd after which magnet was named.
Ans: Magnets.

3. How can you separate a magnetic substance from a mixture?
Ans: By using a bar magnet, the magnetic substance is separated from mixture.

4. At which place on a magnet, its magnetic force is maximum?
Ans: At poles.

5. In which direction does a suspended magnet come to rest?
Ans: Magnet comes to rest in N-S (north-south) direction.

SHORT ANSWER TYPE QUESTIONS

1. Draw the diagram of (a) Bar magnet (b) Horse-shoe magnet.
Ans:

2.Identify magnetic and non-magnetic substances from the list given below: Iron, Steel, Nickel, Plastic, Wood, Copper and a Stainless Steel spoon
Ans:

3. Draw a diagram of a magnetic compass.
Ans:

4. Write main properties of a magnet.
Ans: (i) Magnet has two poles—south pole and north pole.
(ii) Poles of magnet cannot be isolated.
(iii) Like poles repel each other and unlike poles attract each other.
(iv) Freely suspended magnet aligns in N-S direction.

5.Write two methods by which a magnet can be demagnetised.
Ans: (1) By hammering the magnet strongly.
(2) By heating a magnet strongly and keeping it in the east-west direction.