Science Class 6 Chapters 13, 14 and

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1 Chapter 13 Fun with Magnets Magnetic field of the Earth: Geographical North is Magnetic South and vice versa Two places where the magnetic needle becomes vertical are called the magnetic poles. The magnetic equator is the line joining the places where the magnetic needle becomes horizontal. Neutral points are where the magnetic field is equal in magnitude to the earth s horizontal magnetic field If North Pole of magnet faces geographical North, the Neutral points are situated symmetrically on either side of a magnet, at equal distances from the centre, in east-west direction. If NP faces geographical South, Neutral points are symmetrical, in north-south directions. copyright 10x10learning.com 4 1. Fill in the blanks in the following 1.1 Artificial magnets are made in different shapes such as bars and horseshoe. 1.2 The Materials which are attracted towards a magnet are called magnetic. 1.3 Paper is not a magnetic material. ( This question can also be asked as Paper is a non-magnetic material ) 1.4 In olden days, sailors used to find direction by suspending a piece of iron bar. 1.5 A magnet always has two poles. 10x10 Learning TM Page 1

2 2. State whether the following statements are true or false: 2.1 A cylindrical magnet has only one pole. False. 2.2 Artificial magnets were discovered in Greece. False. 2.3 Similar poles of a magnet repel each other. True 2.4 Maximum iron filings stick in the middle of a bar magnet when it is brought near them. False. 2.5 Bar magnets always point towards North-South direction. True. 2.6 A compass can be used to find East-West direction at any place. True. (Because after the north south directions are known, east and west can easily be found. ) 2.7 Rubber is a magnetic material. 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. Answer. The blade in the pencil sharpener is made of steel or iron. Therefore, it is getting attracted by both the poles of a magnet. 4. Write any two properties of a magnet. Answer. Two properties of a magnet are that like poles of two magnets repel each other. Unlike poles attract each other. 5. Where are poles of a bar magnet located? Answer. The poles in a bar magnet are located at the two ends of the bar. 6. A bar magnet has no markings to indicate its poles. How would you find out near which end is its north pole located? Answer. To find out which pole is the north pole in a bar magnet, another magnet whose south pole end is known is be taken near the end of the bar magnet. The north pole end of the bar magnet will be attracted to the south pole end of the second magnet. 10x10 Learning TM Page 2

3 7. You are given an iron strip. How will you make it into a magnet? Answer. There are several methods of making magnets. The simplest method is by rubbing one pole of a magnet from one edge of an iron bar to the other edge. On reaching the other edge magnet is lifted and placed back on the first edge. This is repeated 30 to 40 times. Only the magnet is lifted and rubbed against one surface of iron bar, in one direction. The iron bar is placed in one place. 8. How is a compass used to find directions? Answer. A compass has a magnetized needle that moves over a disc in which North and South are marked. The needle always points to the North Pole. As such, it is very easy to find the north with the help of a compass. Magnetism Magnetism is the power of attracting iron filings and arranging them at the two extreme points of North and South Poles. Unlike poles attract each other and like poles repel one another. Bar magnet, horse shoe magnet, magnetic needle and compass are examples of artificial magnet as magnetism is induced in them. Effective length is the distance between the two poles of a magnet. A magnet can have two equal parts either along its axis or perpendicular to it. No magnet has only one Pole All magnets indicates the direction towards the Magnetic North Pole of the Earth A loadstone found in nature is a natural Magnet. Induced magnetism is when an iron bar behaves like a magnet in the presence of a magnet. On removing the magnet, it no longer shows any properties of a magnet. The space around a magnet in which the needle of a compass rests in a direction other than the geographic north-south direction, is called magnetic field of the magnet. A magnetic field line is a continuous curve in a magnetic field such that tangent at any point of it gives the direction of the magnetic field at that point copyright 10x10learning.com 2 10x10 Learning TM Page 3

4 CHAPTER 14 WATER Formula is H2O Universal Solvent A colourless, tasteless, odourless liquid : 70% of human body and 70% of surface of Earth is made up of water. Vegetables and fruits and vegetation matter contains 60 per cent to 70 % water. Water can exist in all the three states of matter as water, water vapour, and ice. H2O is the formula. This means that two atom of hydrogen join with one atom of oxygen, to create water. Water is a universal solvent. This means it can dissolve the largest number of different kinds of matter. The pleasant taste of water is due to dissolved matter, like air, carbon dioxide, minerals. Distilled water has no taste. Boiling and Freezing points The boiling point of water at sea level, is 100 degree Centigrade. Any increase in atmospheric pressure, raises the boiling point and decrease in atmospheric pressure lowers it. An unusual quality of water is that, when cooled, it first contracts in volume, but at 4 degree C, it starts to expand and continues to expand till it reaches zero degrees. 1. Fill up the blanks in the following: 1.1 The process of changing of water into its vapour is called Evaporation. 1.2 The process of changing water vapour into water is called Condensation. 1.3 No rainfall for a year or more may lead to famine in that region. 1.4 Excessive rains may cause floods. 2. State for each of the following whether it is due to evaporation or condensation: 10x10 Learning TM Page 4

5 2.1 Water drops appear on the outer surface of a glass containing cold water = condensation. 2.2 Steam rising from wet clothes while they are ironed = evaporation. 2.3 Fog appearing on a cold winter morning. = condensation. 2.4 Blackboard dries up after wiping it. = evaporation. 2.5 Steam rising from a hot girdle when water is sprinkled on it = Evaporation. 3. Which of the following statements are true? 3.1 Water vapour is present in air only during the monsoon. False. 3.2 Water evaporates into air from oceans, rivers and lakes but not from the soil. False. 3.3 The process of water changing into its vapour, is called evaporation. True 3.4 The evaporation of water takes place only in sunlight. False. 3.5 Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler. True 4. Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how? Answer. Yes, spreading the uniform near an anghiti or a heater would help because the air around a hot point such as these two, gets warmer more quickly than the surrounding air. The warm air is lighter and rises up. The colder air that is heavier takes its place. This creates a faster cycle of warm and cold air around the anghiti or heater. The cycle helps to dry up the uniform quickly through evaporation. 10x10 Learning TM Page 5

6 5. Take out a cooled bottle of water from refrigerator and keep it on a table. After some time you notice a puddle of water around it. Why? Answer. When the bottle of water is taken out of the refrigerator, it is colder than the air of the room. Therefore, the water vapour present in the warmer air, collects as droplets of water on the surface of the colder bottle due to condensation. The droplets soon flow down to form a puddle at the base of the bottle of water. 6. To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet. Answer. The glasses of the spectacles become misty or wet due to condensation of the water vapour in the breath. The breath is warmer while the glass is cooler. Therefore, the warmer water vapour particles condense in to a mist on the glasses. 7. How are clouds formed? Answer. The seas and oceans cover 70 per cent of surface of the Earth. Water continuously gets evaporated over all the water surfaces. The water vapour is warmer and lighter and it rises to the higher layers of the atmosphere. There it gets cooled to form clouds. 8. When does a drought occur? Answer. Drought occurs when the seasonal rainfall in a region fails to occur. In India, seasonal rainfall is limited to four months of South West monsoon. This period is from June to September. The moisture laden south west winds move towards India to bring monsoon rains. If these winds get diverted, they fail to bring rainfall in India or parts of India. This results in drought. 10x10 Learning TM Page 6

7 CHAPTER 15 AIR AROUND US 1. What is the composition of air? Answer. The air is a mixture of many gases and harmful particles. The most important gases are water vapour, oxygen, nitrogen, carbon dioxide. The harmful particles are of dust and smoke, emissions from vehicles and industries. 2. Which gas in the atmosphere is essential for respiration? Answer. Oxygen is most essential for respiration. 3. How will you prove that air supports burning? Answer. Oxygen in the air is needed for burning. This can be proved by lighting a candle and covering it with a glass container or tumbler. After the limit air inside the tumbler is used up by the burning candle, the candle blows off by itself. This proves that air is needed for burning. 4. How will you show that air is dissolved in water? Answer. If some water is placed on fire for boiling, tiny bubbles are formed at the bottom of the container. The bubbles are of air in the water, converting into water vapour. When the water is boiling fully, larger bubbles of air can be seen as the air escapes from the water in the form of vapour. This shows that air is dissolved in water. 5. Why does a lump of cotton wool shrink in water? Answer. A lump of cotton wool shrinks in water because the air between its fibres, escapes and gets replaced by the heavier drops of water. 6. Fill in the blanks: 10x10 Learning TM Page 7

8 7. The layer of air around the earth is known as atmosphere. 8. The component of air used by green plants to make their food is carbon dioxide. 9. List five activities that are possible due to the presence of air. Answer. Five things possible due to the presence of air are: 1. All life forms are able to breathe and continue to live. 2. Fire burns for cooking food. 3. Plants produce their food in the presence of air and sunlight. This plant food is then eaten by birds, animals, insects and humans. 4. Water life and marine life exist because of air mixed in the water 5. Rainfall occurs due to presence of air and winds. 10. How do plants and animals help each other in the exchange of gases in the atmosphere? Answer. In the presence of sunlight, plants absorb carbon dioxide from the air, and break it into oxygen and carbon. Oxygen is thrown back into the air, and is used by other animals for breathing. Animals breathe out carbon dioxide. This carbon dioxide is again absorbed by plants. In this way plants and animals help each other in exchange of oxygen and carbon dioxide. 10x10 Learning TM Page 8

13. Fun with Magnets

13. Fun with Magnets 1. Fill in the blanks in the following (i) Artificial magnets are made in different shapes such as bar magnets, horse-shoe magnet and cylindrical or a ball-ended magnet. (ii) The Materials