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# Electric spark

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Electric spark

Electric spark

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• 1. OMTEX CLASSES SCIENCE AND TECHNOLOGY ELECTRIC SPARK FILL IN THE BLANKS State True or False. If false correct it. Match the column. GIVE SCIENTIFIC REASONS The material used for fuse has low melting point. Wood and glass are good insulators. The melting point of filament of a bulb is very high. Connecting wires in a circuit are made of copper and aluminium. Lightning occurs from sky to earth. Nichrome wire is used in heating device. A parallel combination of resistance decreases the effective resistance of the circuit. A series combination of resistances is used to increase the resistance of a circuit. A thick wire has a low resistance.
• 2. OMTEX CLASSES SCIENCE AND TECHNOLOGY Metals are good conductors of electricity. DEFINE 1 volt 1 ampere: 1 ohm: Potential: Resistivity: Electric power: 1 watt power. Joule’s law. Resistance. Insulators. Conductors. DISTINGUISH BETWEEN Resistances in series and parallel. Conductors and insulators. Resistance and resistivity. High resistance and low resistance. LAW'S Ohm’s law
• 3. OMTEX CLASSES SCIENCE AND TECHNOLOGY Joule’s law ANSWER IN BRIEF Resistors connected in Series Resistance connected in parallel Find the expression for resistivity of a material. P and Q are the two wires of same length and different cross sectional areas and made of same metal. Name the property which is same for both the wires and that which is different for both the wires. Resistivity of some material is given below. which one will be the best conductor.... If the resistance of wire A is four times the resistance of wire B, find the ratio of their cross sectional areas. Two dissimilar bulbs are connected in series, bulb will be brighter? (Hint: consider the resistance of the bulb). Explain why a conductor is heated when current flows through it. Explain the concept of resistance. Explain the working of electric fuse. Explain the working of electric iron.
• 4. OMTEX CLASSES SCIENCE AND TECHNOLOGY Flow of current through conductors. Electrical symbols used in electrical circuits Fuse is always connected in series. Why ? Why tungsten wire is not used in electric fuse ? Heating appliances consume more electricity. Why ? Why the commercial unit of power is different from its SI unit ? A mica sheet is used in an electrical iron. Why ? How are electrical appliances connected at home ? Why ? If the length of a copper wire is doubled and its radius is halved, what is the effect on its resistivity ? Ramesh connected number of bulbs with a nichrome wire whereas Suresh connected all the bulbs with copper wire of the same length and thickness. In whose case will the bulbs be brighter ? State the characteristics of connecting resistances in parallel. State the characteristics of connecting resistances in series.