1 List the factors on which the resistance of a conductor in the shape of a wire depends.
2. Why are alloys commonly used in electric heating devices? Given reason. [
3. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series ?
4. Why are the coils of electric toasters and electric irons made of an alloy rather than a pure metal
5. Why does the cord of an electric heater not glow while the heating element does?
6. How does use of a fuse wire protect electrical appliances?
7. Why is parallel arrangement used in domestic wiring?
8. What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 5 A. The reading of the ammeter decreases to half when the length of the wire is doubled. Why?
Answers
Answer:
1) The resistance of the conductor depends on the following factors:
(a) The temperature of the conductor.
(b)The cross-sectional area of the conductor.
(c)Length of the conductor.
(d)Nature of the material of the conductor.
2) Most electrical heating devices use alloys because they have high resistivity and the melting point is also high in them.
3) There is no division of voltage among the appliances when connected in parallel. The potential difference across each appliance is equal to the supplied voltage. The total effective resistance of the circuit can be reduced by connecting electrical appliances in parallel.
4) Coils of electric toasters and electric irons made of an alloy rather than a pure metal due to the following reasons: The resistivity of an alloy is higher than the pure metal. ... Alloy does not melt readily and get deformed. Alloys have a low-temperature coefficient of resistance.
5) The heating element of the heater is made up of alloy which has very high resistance so when current flows through the heating element, it becomes too hot and glows red. But the resistance of cord which is usually of copper or aluminum is very low so it does not glow.
6) The fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily.
7) The fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily.
8) Electrical resistivity is the property of the material independent of the geometry of conductor. It is basically resistance for a given area of cross-section of conductor per unit length. When length of wire is doubled, the resistance is also doubled, because resistance is directly proportional to length of wire. Hence according to ohms law for a given potential difference, the current reduces to half.