CBSE ADDA

Microorganisms Definition The organisms which cannot be observed with the naked eye and can be seen only through a microscope are called microorganisms or microbes. Food and water become unsafe for consumption due to the presence of harmful organisms, commonly referred to as germs . These germs are so small that they are invisible to the naked eye, but can often cause dangerous diseases. Since these organisms can be seen only through a microscope, they are called microorganisms or microbes. When the body is attacked by germs or pathogens, medicines called antibiotics are given. Antibiotics act against the bacteria within the body, without harming the person. Microorganisms Microorganisms are present in the air, water, food and even inside our bodies. While a majority of the microbes are harmless, some of them have the capability of causing dangerous diseases. Microorganisms Bacteria Algae Fungi Protozoa Vir

8 th synthetic materials Þ          Synthetic materials are kinds of materials obtained from the synthesis of chemicals. Þ      The chemicals used for synthetic materials are obtained from petroleum and natural gas(methane) Þ      Petroleum and natural gas is compound of hydrogen and oxygen called hydrocarbon. Þ      Monomers are simple chemical molecules of hydrocarbon. Þ      When monomers join end to end form a long chain of monomers called polymers. The process of the formation of polymers is called polymerization. Þ      Cellulose [beet root] is polymers of glucose while Hemoglobin is polymers of amino acid. Þ      Fibres are thin thread like materials used to prepared cloths. Þ      Fibres obtained on mixing natural and synthetic fiber are called semi synthetic fibre. e.g. rayon Rayon Þ      Rayon is synthetic fibres obtained from cellulose. Þ      Rayon are of three types: Viscose Cupreammonium (cupro)  and acetate rayons. Viscose Rayon Þ      In ind

Force A force is an agent which can change or try to change the state of an object. Force is the product of  mass and acceleration F = ma Force has both magnitude and direction, making it a vector quantity. The SI unit used to measure force is the Newton (symbol N), which is equivalent to kg•m•s-2 Actions like picking, opening, shutting, kicking, hitting, lifting, flicking, pushing, pulling are often used to describe certain tasks. Each of these actions usually results in some kind of change in the motion of an object. A force is a push or pull upon an object resulting from the object's interaction with another object.   Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction. All forces (interactions) between objects can be placed into two broad categories: • Contact forces, and • Non Contact for

1. The current passing through a room heater has been halved. What will happen to the heat produced by it? 2. An electric iron of resistance 20 ohm draws a current of 5 amperes. Calculate the heat produced in 30 seconds. 3. An electric heater of resistance 8 ohm takes a current of 15 A from the mains supply line. Calculate the rate at which heat is developed in the heater. 4. A resistance of 40 ohms and one of 60 ohms are arranged in series across 220 volt supply. Find the heat in joules produced by this combination in half a minute. 5. A resistance of 25 ohm is connected to a 12 V battery. Calculate the heat energy in joules generated per minute. 6. 100 joules of heat is produced per second in a 4 ohm resistor. What is the potential difference across the resistor? 7. An electric iron is connected to the mains power supply of 220 V. When the electric iron is adjusted at minimum heating’ it consumes a power of 360 W but at ‘maximum heating’ it takes a power of 840 W. Ca