Download Science - St. Paul H. S. School, Indore

Science study material (FA – IV )
CLASS - VI
CHAPTER 12- ELECTRICITY AND CIRCUITS
V. 1. (a) Electric heater and electric oven are cookingdevices.
(b)
Electric bulb and fluorescent tubelight are lighting devices.
(c)
Loudspeaker and tape recorder are sound produc-ing devices.
2. The complete path from one terminal of an electric cell through the bulb and back to the other terminal
of the electric cell is called Electric circuit.
3.
4.
Activity 8, page 152.
A device by which an electric circuit can easily be completed or broken is called electric switch.
An electric switch helps to start or stop electric appliances when required without disconnecting the
wires in the electric circuit.
5.
When main switch is put off, the current coming from power station stops flowing in the household
circuit. Thus, all appliances stop working.
6.
A cell is a device which converts chemical energy into electric energy when placed in a closed electric
circuit. A combination of two or more cells connected to an electric circuit is called ‘battery’.
Refer to Fig 12.6, page 147.
7.
CHAPTER 13- FUN WITH MAGNETS
1.
A piece of iron or steel which attracts other pieces ofiron towards itself is called magnet.
A permanent magnet is made from steel and does not lose its magnetism. However, a
temporary magnet is made from pure iron and it looses its magnetism quickly
Steel, nickel and cobalt are used for making permanent magnets.
2.
(i) The north pole of needle moves away from the magnet.
(ii)
The north pole of needle moves towards the magnet.
3. It can be struck on steel cupboard or iron object.
4. Shaving blade, steel cupboard and blade of knife are magnetic substances. A plastic ruler, a brass
button, a piece of chalk, a plastic mug, water and wooden stick are non-magnetic substances.
5. The main properties are attractive property (attracting pieces of iron towards itself) and directive
property (pointing in north-south direction when freely suspended).
6. A magnet which occurs naturally and it is not made by any artificial means is called a natural magnet.
Example : Magnetite.
A substance to which properties of the natural magnet are imparted by artificial means is called is called
artificial magnet. Example : The magnets made from iron, steel, cobalt or nickel are called artificial
magnets.
7. Attraction can be caused by (i) a pole of magnet and iron articles (ii) opposite poles of a magnet.
However, repulsion is caused by two similar poles of two magnets. Thus, repulsion is the surest test of
magnetism.
8.(i) It attracts small pieces of iron and steel towards itself.
(ii)
It points in North-South direction when freely suspended
(iii) When broken, each piece is a complete magnet.
(iv) when rubbed over unmagnitised piece of steel, it magnetises it.
9.Refer to Article 13.4 (page 161).
10.
(i) By placing two magnets such that their similar poles face each other.
(ii)
By heating or rough handling.
11. The bar magnets should be stored in pairs in a wooden box, separated by a piece of wood, such that
their opposite ends face each other. Furthermore, pieces of iron should be placed at both the ends. These
pieces of iron are commonly called magnetic keepers.
12. Bring each end of the bar magnet near the North Pole of a freely suspended magnetic needle. The end
of bar magnet which shows repulsion is north pole of bar magnet.
CHAPTER 14 – WATER
1. To Show the presence of water vapour in air
Material required : Clean glass tumbler and ice cubes
Method : Place a few ice cubes inside the clean glass tumbler. After few minutes we will notice that
the outer surface of the glass tumbler becomes misty and finally droplets of water appear on it.
Conclusion : It is because as the air around the glass tumbler cools, the water vapour in air condenses
to form tiny droplets of water, which deposit themselves on the outer surface of glass tumbler.
2. Ocean water is salty, inspite of it, ocean water is the major source of fresh water on earth
because by the process of evaporation oceans add large amount of water vapours to the air. These
water vapours changes back to liquid state by the process of condensation.
Thus, we get fresh water.
3. The plants add water vapour in air by the process of transpiration. Plants absorb water from
the soilwith the help of their roots. The surplus water is released into the air through their leaves by
the process of transpiration.
4. Trees add water vapour to air by the process of transpiration. By deforestation the amount of
water vapour will decrease and this will cause less rain.
5. Clouds are made of droplets of water, ice crystals, particles of dust and air. The lower part of
Earth‘s atmosphere is full of water vapour. The warm air being lighter rises up and cools down. The
warm air can hold large amount of water vapour. However, when this air cools down high up in the
atmosphere, it can no longer hold a large amount of water vapour. Thus , the excess water vapour
condenseson dust particles to form the clouds.
6. Four harmful effects of excessive rains :
i) Water level in rivers, lakes and ponds rises.
ii) Heavy rains cause floods which cause soil erosion making the land barren and infertile.
iii) It leads to a loss of crops and other food items.
iv) Flood water mixes with waste material and leads to many diseases.
7. Water should be conserved as fresh water is much less on the earth than what we
need. Rain water harvesting is a technique to collect as much water as possible during
the rainy season for future use. In this system rainwater from the rooftop is brought
down by a pipe which emptiesitself in the filter tank containing sand and pebbles.
The water from filter tank is then made to seep into another tank for storage.