Science
In our homes, we receive the supply of electric power through a main supply also called mains, either supported through overhead electric poles or by underground cables. In our country the potential difference between the two wires (live wire and neutral wire) of this supply is 220 V.
(a) Write the colours of the insulation covers of the line wires through which supply comes to our homes.
(b) What should be the current rating of the electric circuit (220 V) so that an electric iron of 1 kW power rating can be operated ?
(c) What is the function of the earth wire? State the advantage of the earth wire in domestic electric appliances such as electric iron.
OR
(c) List two precautions to be taken to avoid electrical accidents. State how these precautions prevent possible damage to the circuit/appliance.
Related Questions
(a) The power of a lens 'X' is -2·5 D. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens ?
(b) "The value of magnification 'm' for a lens is -2." Using new Cartesian Sign Convention and considering that an object is placed at a distance of 20 cm from the optical centre of this lens, state :
- the nature of the image formed;
- size of the image compared to the size of the object;
- position of the image, and
- sign of the height of the image.
(c) The numerical values of the focal lengths of two lenses A and B are 10 cm and 20 cm respectively. Which one of the two will show higher degree of convergence/divergence? Give reason to justify your answer.
(a) Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass.
(b) State Snell’s law of refraction of light.
(c) Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of :
- object distance, and
- magnification
Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.
(a) Write balanced chemical equations to show the products formed during electrolysis of brine.
(b) List two uses of any one product obtained during electrolysis of brine.
(c) A mild non-corrosive basic salt ‘A’, used for faster cooking, is strongly heated to produce a compound ‘B’, that is used for removing permanent hardness of water. Identify A and B and also write the equation for the reaction that occurs when A is heated.
OR
(c) Define water of crystallisation. Give two examples of salts that have water of crystallisation.
The maintenance functions of all living organisms must go on even when they are not doing anything particular. Even when we are just sitting in a class or even asleep, this maintenance job has to go on. These maintenance processes require energy to prevent damage and break-down of cells and tissues, which is obtained by the individual organism from the food prepared by the autotrophs, called producers.
(a) Name and define the process by which green plants prepare food.
(b) Write chemical equation involved in the above process.
(c) State in proper sequence the events that occur in synthesis of food by desert plants.
OR
(c) Explain giving reasons what happens to the rate at which the green plants will prepare food
- during cloudy weather, and
- when stomata get blocked due to dust.