Grade 10 Science Electricity Notes - NCERT PDF

Chapter:11 ELECTRICITY (Printed Notes) class: X Page No: 172 Q1. What does an electric circuit mean? Ans: A continuous closed path along which an electric current flow is called an electric circuit. Q2. Define the unit of cu...

Chapter:11 ELECTRICITY (Printed Notes) class: X Page No: 172 Q1. What does an electric circuit mean? Ans: A continuous closed path along which an electric current flow is called an electric circuit. Q2. Define the unit of current. Ans: The S.I unit of current is ‘Ampere’. When one coulomb of charge flows through any section of a conductor in one second then the current through it is said to be one ampere. I = Q/t or 1 A = I C /s. Page No: 174 Q2. What is meant by saying that the potential difference between two points is IV? Ans: The potential difference between two points is said to be 1 volt, if 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other. Page No:181 Q2. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why? Ans: The current will flow more easily through a thick wire, than a thin wire of the same material. Larger the area of cross-section of a conductor more is the ease with which the electrons can move through the conductor. Therefore, smaller is the resistance of the conductor. Q3. Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it? Ans: When potential difference is halved, the current through the component also decreases to half of its initial value. This is according to ohm’s law i.e., V ∝ I. Q4. Why are coils of electric toasters and electric irons are made of an alloy rather than a pure metal? Ans: The coils of electric toasters, electric irons and other heating devices are made of an alloy rather than a pure metal because (i) the resistivity of an alloy is much higher than that of a pure metal, and (ii) an alloy does not undergo oxidation (or burn) easily even at high temperature, when it is red hot. Q5. Use the data in Table 12.2 (in NCERT Book on Page No. 207) to answer the following : (a) Which among iron and mercury is a better conductor? (b) Which material is the best conductor? Ans: (a) Resistivity of iron = 10.0 x 10-8 Ω m Resistivity of mercury = 94.0 x 10-8 Ω m. Thus, iron is a better conductor because it has lower resistivity than mercury. (b) Because silver has the lowest resistivity of 1.60 x 10-8 Ω m, therefore silver is the best conductor. Page No: 188 Q3. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series? Ans: Advantages of connecting electrical devices in parallel with the battery are: ➔ In parallel circuits, if an electrical appliance stops working due to some defect, then all other appliances keep working normally. ➔ In parallel circuits, each electrical appliance has its own switch due to which it can be turned on turned off independently, without affecting other appliances. ➔ In parallel circuits, each electrical appliance gets the same voltage (220 V) as that of the power supply line.  ➔ In the parallel connection of electrical appliances, the overall resistance of the household circuit is reduced due to which the current from the power supply is high. Page No: 190 Q1. Why does the cord of an electric heater not glow while the heating element does? Ans: The heating element of an electric heater made of nichrome glows because it becomes red-hot due to the large amount of heat produced on passing current because of its high resistance, but the cord of the electric heater made of copper does not glow because negligible heat is produced in it by passing current because of its extremely low resistance. Page Number: 192 Q1. What determines the rate at which energy is delivered by a current? Ans: Resistance of the circuit determines the rate at which energy is delivered by a current. Page Number: 194 Q18. Explain the following: (a) Why is tungsten used almost exclusively for filament of electric lamps? (b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal? (c) Why is the series arrangement not used for domestic circuits? (iv) How does the resistance of a wire vary with its area of cross-section? (v) Why are copper and aluminium wires usually employed for electricity transmission? Ans: (i) The tungsten is used almost exclusively for filament of electric lamps because it has a very high melting point (3300°C). On passing electricity through tungsten filament, its temperature reaches to 2700°C and it gives heat and light energy without melting. (ii) The conductors of electric heating devices such as bread-toasters and electric irons, are made of an alloy rather than a pure metal because the resistivity of an alloy is much higher than that of pure metal and an alloy does not undergo oxidation (or burn) easily even at high temperature. (iii) The series arrangement is not used for domestic circuits because in series circuit, if one electrical appliance stops working due to some defect, than all other appliances also stop working because the whole circuit is broken. (iv) The resistance of a wire is inversely proportional to its area of cross-section, i.e., Resistance R ∝ (1/πr2). If the area of cross section of a conductor of fixed length is increased, then resistance decreases because there are more free electrons for movement in conductor. (v) Copper and aluminium wires usually employed for electricity transmission because they have very low resistances. So, they do not become too hot on passing electric current.