Chapter : 13 Topic : Electricity and Circuits

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CLASS 6

, TERM – II (SSM) SUBJECT: SCIENCE

Chapter : 13

Topic : Electricity and Circuits

C. Short Answer Questions

1. We should not operate electrical switches with wet hands because we can get an electric shock. As water is a conductor of electricity, so water on the wet hands may conduct some electricity from the switch into our body and thus can lead to fatal consequences.

2. The Circuit in which the path from one terminal of cell to another terminal of cell is incomplete and the electric current does not flow through it is called an open circuit.

3. Do it yourself 4. Do it yourself.

5. When the switch is in 'on' position, the electric circuit is complete and the current is allowed to flow through the circuit.

When the switch is in 'off' position, the circuit is incomplete and the current does not flow through the circuit

D. LONG ANSWER QUESTIONS

1. An electric bulb has an outer case made of glass that is fixed on a metallic base. It consists of a tiny, thin wire called a

filament. The filament is made up of

tungsten and is fixed to two thick

wires. One of these thick wires is

connected to the metal case at the

base of the bulb. The other thick wire

is connected to the metal tip at the

centre of the base. The metal tip at

the centre of the base and the metal

casing at its lower end act as

terminals of the bulb.

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2. The materials that allow electric current to pass through them are called conductors. Metals are good conductors of electricity. Among non-metals, only graphite is a good conductor of electricity. Switches, electrical plugs and sockets are made up of conductors. While as, the materials that do not allow electric current to pass through them are called insulators. Rubber, plastic, wood and glass are some examples of insulators. The covering of electrical wires, plug tops, switches and other parts of electrical appliances that people might touch are made from insulators like rubber or plastic.

3. Electric current flows when one or more cells are connected to other components such as bulb by electric wires in an unbroken (or complete) closed loop. Such an unbroken loop is called electric circuit. Thus, the electric circuit provides a complete path for electricity to pass between the terminals of an electric cell. In an electric circuit, the direction of flow of electricity is taken to be from the positive terminal of the cell to the negative terminal of the cell.

A Simple device used to open or close an electric circuit is called electric switch.

When the key is closed, the electric circuit is complete and the current is allowed to flow through the circuit. The appliance (like a bulb or a fan), which is the part of the circuit, works. When the key is open, the circuit is incomplete, no current flows and the appliance does not work.

4. Do it yourself.

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Chapter : 14 Topic : Magnetism C. Short Answer Questions:

1. Do it yourself.

2. Do it yourself.

3.

Natural Magnets Artificial Magnets

1. Natural magnets are those magnets which occur naturally in nature.

Artificial magnets are those magnets which are made by humans.

2. These magnets generally have low magnetic power.

These magnets have strong magnetic power.

3. Natural magnets are permanent magnets.

Artificial magnets may be either permanent or temporary magnets.

4. Magnetite is an example of natural magnet.

Bar magnet, horse shoe magnet are some examples of artificial magnets.

4. A freely suspended magnet always rests pointing in the north-south direction. This property of a magnet is called its directive property.

5. To prove repulsion is a sure test for magnetism, an activity needs to be performed.

Things needed : Bar magnet, metallic bar, thread.

Take a bar magnet. Suspend it with the help of a thread. Now, bring one end of a metallic bar near one pole of the suspended magnet at a time. If one end of the metallic bar is attracted and the other is repelled, the metallic bar is a magnet. If both the ends of the metallic bar are attracted, then it is not a magnet. Thus, it proves Repulsion is a sure test for magnetism.

6. Do it yourself.

D. LONG ANSWER QUESTIONS.

1. To make a magnetic compass.

Things needed: A sewing needle, a bar magnet, a cork or rubber and a cup.

Method: Magnetise a sewing needle with a bar magnet. Pass the magnetised

needle through a small piece of cork or rubber. Place this cork containing the

magnetised needle in a cup containing water. Make sure that the needle does not

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touch water. When the needle comes to rest, it points to the north-south direction.

Rotate the cork with the needle inserted in it in different directions.

Observation: It would be observed that the needle always points to the north- south direction. Thus, the magnetic compass is ready for use.

2. The ends of a magnet, where the magnetic force is the strongest, are called its poles. A magnet has always two poles. The two poles of magnet are near its free ends. The pole of the magnet that points towards the north is called the north pole of the magnet. The other end that points towards the south is called the south pole of the magnet. Usually, the north and south poles are marked on the magnet as 'N' and 'S'. The north and South Pole of a magnet always exist together. Every magnet whether small or big has a north pole and a south pole. It is impossible to have a magnet having only one pole.

3. Do it yourself

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CHAPTER : 15 WATER Short Answer Questions:

1. The process of release of extra water in plants into the air in the form of water vapour’s through aerial parts is called transpiration.

2. Absence of rain in a particular region for a long time, leading to severe shortage of water is called drought.

3. (a) The problem of water shortage is increasing day by day due to increasing population.

(b) Puja cares for her neighbours and helps all.

4. The reservoir of water collected over the hard, non porous rock below the surface of earth is called ground water.

Long answer questions:

1. Rain is useful to us because

I. It brings relief by cooling the environment especially after hot summer days.

II. It is important for irrigating the crops in fields.

III. It maintains the supply of water on land by filling lakes, ponds and raising the water table.

2. The life of animals living in soil get affected by heavy rains, as the land gets covered in water. The animals (snake and earthworms) that live in soil come out in search of air and food.

3. The main purpose of rain water harvesting is not only to hold rainwater on the surface of earth but also to make rainwater percolate under the ground more efficiently so as to recharge ground water. This ground water can be taken out through various underground water sources like tube wells, hand pumps, etc. as and when required .The advantage of rain water is that it increases the availability of ground water and helps in overcoming water shortage.

The other advantages of rainwater harvesting are

I. Soil erosion can be checked by rainwater harvesting.

II. It helps to control flood.

III. Dry months also avail water supply for irrigation and other purposes.

IV. It reduces the run off loss of rain water.

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4. (a)The trees absorb water from the soil through their roots. They release excess water as water vapours by the process of transpiration. This water vapour goes into the air and form clouds. The roots of trees also help in deep percolation of rainwater and thus enrich the water table.

(b)The flood water submerge the standing crops, grasslands and forests. Due to this the plant does not get sufficient amount of air and nutrients and die.

(c) The problems faced by people after floods are:

I. Floods in city areas leads to water logged roads and streets. This disrupts the traffic on roads and cause inconvenience to people.

II. Flood causes extensive damage to crops. This may cause acute food shortage and deaths due to hunger.

III. Flood causes serious injuries or deaths of domestic animals by drowning.

IV. When flood water recedes, it causes spreading of diseases like cholera, dysentery, diarrhea, etc.

V. Flood washes away top layer of soil thus reduces fertility of soil.

5. (a) As the population is increasing rapidly, the number of people using water is also increasing day by day. Also more and more water is used in agriculture for producing food and by the industries which manufactures a large variety of products for our use .All the factors are leading to shortage of water in many parts of world including our country. Keeping in view the shortage of usable water, it is essential that water is used carefully. We should take care not to waste water.

(b) The ways to conserve water are:

I. Plant more and more trees.

II. Use a bucket and a mug instead of shower while taking bath.

III. Close the taps tightly after using them.

IV. Avoid cleaning utensils under running water.

V. Check overflowing of water tanks.

VI. Recycle waste water.

VII. Adopt rainwater harvesting to store the rain water.

(c) The two main types of rainwater harvesting are:

I. Rooftop rainwater harvesting.

II. Roadside rainwater harvesting

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HOTS (Higher Order Thinking Skills) Questions:

1. Flood and drought damage the crops and create acute food shortage leading to increase prices of food grains, fruits and vegetables.

2. (a) Fog in cold winter mornings reduce visibility due to which several accidents take place.

(b) Presence of tiny drops of dew on grass

(c) Rain maintains the supply of water on land by filling lakes, ponds, and streams and raising the water table.

(d) Ground becomes submerged under water during flood which causes extensive damage to human life and property.

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CHAPTER 16 - AIR AROUND US C. Short answer questions:

1. (a)water vapour (b)Dust smoke and gases especially carbon dioxide and oxides of nitrogen and sulphur.

2. The blanket of air that surrounds the earth is called atmosphere. The major components of air are nitrogen. Oxygen, carbon dioxide, and few other gases, water vapour and dust particles.

3. (a)The doctor provides extra oxygen to priyanka’s uncle by an oxygen cylinder.

(b)Care for others and taking quick decisions.

4. Nitrogen is needed by living organisms as it forms various components of the body of living organisms like proteins and nucleic acids.

5. If there is no air in water, the aquatic animals and plants will die. In the absence of oxygen, the aquatic animals will be unable to breathe. The aquatic plants will also be unable to perform photosynthesis and respiration.

6. Air helps in maintaining proper temperature on the earth. When sun rays falls on earth, some of them get absorbed by atmosphere and rest are reflected back. This trapped heat prevents earth’s atmosphere from too much cooling and maintain appropriate temperature.

7. The air around the glass contains water vapour. The cold surface of the glass containing the ice cools the air around it and the water vapour of the air condenses on the outer surface of the glass. This occurs due to condensation.

D. Long answer questions:

1. Animals inhale oxygen from air and exhale carbon dioxide which goes into the air. The burning of fuel uses oxygen from the air and gives out carbon dioxide.

Green plants use carbon dioxide from the air for the process called photosynthesis during day and give out oxygen. The process of respiration in plants takes place during day as well as night. But during day, the oxygen released during photosynthesis is more than the oxygen used in respiration.

Therefore the oxygen is released in the atmosphere .In the above mentioned ways, plants and animals maintain the balance of oxygen and carbon dioxide in the air.

2. To show the presence of air in water

Things needed: A beaker, tripod stand, a burner, some water.

Method: Take some water in a beaker and keep it on tripod stand. Heat the water slowly by using a burner.

You will observe that, much before the water begins to boil; tiny bubbles

appear on the inner side of the beaker. These bubbles come from the air

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dissolved in water. Actually, when water is heated, the solubility of air in it decreases. As a result the air dissolved comes out in the form of tiny bubbles.

When the dissolved gas has been driven off through heating and the same water is heated again after short interval of time we do not observe bubbles. On further heating, water itself turns into vapour and finally, begins to boil. It shows that air is dissolved in water.

3. (a) No, all organisms do not breathe through lungs. Most of the terrestrial organisms breathe through lungs.

(b)The aquatic organisms take oxygen dissolved in water for breathing.

4. The air is useful to us in many ways. The major uses are as follows:

I. Oxygen is used by all living organisms for respiration.

II. Oxygen is necessary for burning fuels.

III. Compressed air is used for inflating tyres of bicycles, scooters, cars, and busses. It is also used in balloons footballs etc.

IV. Moving air has force. This force helps yachts (sailing boats), parachutes and gliders to move.

V. Moving air (wind) is used to turn the blades of windmills. A windmill is used to draw water from tube wells to run flour mills and generate electricity.

VI. Wind helps in the dispersal of seed in plants. It also helps in pollination.

E. HOTS (high order thinking skill) questions:

1. We should breathe through nose because the fine hair and mucus present inside the nose prevent dust particles to enter our lungs. If we breathe through mouth, harmful dust particles and germs may enter our body and affect our health.

2. Some insects live in soil, come out of the soil during heavy rain because rain water fills up all the spaces occupied by the air in the soil and no air is left in the soil to breathe.

3. Coastal areas are surrounded with sea and evaporation of sea water increases the humidity of environment and makes the weather more humid than the central region where sea is not found.

4. We can improve the air quality of our locality by : I. Planting more and more trees.

II. Using cleaner fuels like CNG vehicles instead of petrol and diesel.

III. Reducing the use of vehicle running with petrol and diesel.

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IV. Using smokeless sources of energy such as tidal energy and solar energy.

V. Walking and using rickshaw or bicycle for shorter distances.

5. During the day, the rate of photosynthesis in plants is much more than the rate of respiration. In day time, the total carbon dioxide produced during respiration is used by plants in photosynthesis thus carbon dioxide is not released in the environment. At night, no photosynthesis but only respiration takes place. Thus, only carbon dioxide is released by plants. We also produce carbon dioxide during breathing .Thus it is advised not to sleep under the trees at night because it can cause suffocation and breathlessness.