Seating plan for Cycle Test - 1
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Science Class 8 : Fuel Fire and Flame
Fuel, Fire and Flame Q1. You are provided with three watch glasses containing milk,petrol and mustard oil, respectively. Suppose you bring a burning candle near these materials one by one, which material(s) will catch fire instantly and why? Ans. Petrol will catch fire instantly because it is highly inflammable and its ignition temperature is very less as compared to other substance. Ignition temperature is the lowest temperature at which the substance catches fire. Q2. What are the essential requirements to produce fire? How fire extinguisher is useful for controlling fire. Ans. Three essential requirements. a. Fuel b. Air c. Heat to acquire the ignition temperature. Flames need fuel oxygen and heat in order to burn. Fire extinguishers are designed to remove one of these elements by applying an agent that either cools the burning fuel, or removes or displaces the surrounding oxygen. Q3. Give two examples each for a
Science Class 8 Friction : A necessary evil
Friction : A necessary evil Q1. When the cutting edge of a knife is put against a fast-rotating stone to sharpen it, sparks are seen to fly. Explain the reason. Ans. Friction generates heat. When the cutting edge of a knife comes in contact with a fast rotating stone, heat is produced due to friction between the grinding stone and the cutting edge of the knife. As the friction is very large, a large amount of heat is produced and sparks are seen flying while sharpening the cutting edge of the knife. Q2. We have two identical metal sheets.One of them is rubbed with sand paper and other with ordinary paper. The one rubbed with sand paper shines more than the other. Give reason. Ans. The friction between the sand paper and the metal sheet is very large as compared to that between the ordinary paper and metal sheet. The sand paper is able to remove the outer dull layer from the metal sheet more effectively. Therefore, the
Science: Forces in action
Force in Action Q 1 Explain the construction and working of Manometer. Ans. Manometer is a device which is used to measure the pressure exterted by liquids. Construction : It consists of a U-tube made of glasses or transparent polythene with both its ends open, fixed vertically on a stand. Filled with colored water or mercury. A plastic funnel is fixed at one end of the tube and covered with rubber balloon sheath. Working : When dipped inside the container having liquid in it the level of mercury changes and the difference between the initial and final level of the mercury shows the pressure exerted by the liquid. Q2 Give two examples each of situation in which you push or pull to change the state of motion of objects. Ans . Two examples of push force are as follows : - A heavy box at rest is pushed to move it from one room to another. This changes the state of motion of the box. - A player pushes a football
