Class 10 › Science Electricity Class 10 Science · Chapter 11
Practice all → Summary Questions & answers Practise this chapter → View all Electric current is the flow of electric charge, driven by a potential difference and measured with an ammeter, while potential difference is measured with a voltmeter. Ohm’s law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across it (V = IR), where R is the resistance. Resistance depends on a material’s length, area and resistivity. Resistors can be combined in series, where resistances add, or in parallel, where the net resistance is smaller than the least. The heating effect of current (H = I²Rt) explains devices like electric heaters and the working of fuses, while electric power (P = VI) and energy (measured in kilowatt-hours) describe how much electricity an appliance uses. These ideas underpin all domestic and industrial wiring.
Electric current
Rate of flow of electric charge, measured in amperes.
Ohm’s law
\(V = IR\) — current is proportional to potential difference at constant temperature.
Resistance
Opposition to current flow, measured in ohms.
Electric power
Rate of consuming electrical energy, \(P = VI\).
Q1 Why are series circuits not used for domestic wiring? Answer Q2 Why is tungsten used for the filament of an electric bulb? Answer Q3 Define electric current and state its SI unit. Answer Q4 What is potential difference, and how is it measured? Answer Q6 On what factors does the resistance of a conductor depend? Answer Q7 How does the net resistance change in series and in parallel? Answer Q8 Why is parallel arrangement used in domestic wiring? Answer Q9 State the heating effect of current and one application. Answer Q10 Define electric power and the commercial unit of electrical energy. Answer Q1 1. What does an electric circuit mean? Answer Q2 2. Define the unit of current. Answer Q3 3. Calculate the number of electrons constituting one coulomb of charge. Answer Q1 1. Name a device that helps to maintain a potential difference across a conductor. Answer Q2 2. What is meant by saying that the potential difference between two points is 1
,
mathrmV? Answer Q3 3. How much energy is given to each coulomb of charge passing through a 6
,
mathrmV battery? Answer Q1 1. On what factors does the resistance of a conductor depend? Answer Q2 2. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why? Answer Q3 3. 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? Answer Q4 4. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal? Answer Q5 5. Use the data in Table 11.2 to answer the following – (a) Which among iron and mercury is a better conductor? Answer Q6 (b) Which material is the best conductor? Answer Q1 1. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2
,
mathrmV each, a 5
,
Omega resistor, an 8
,
Omega resistor, and a 12
,
Omega resistor, and a plug key, all connected in series. Answer Q2 2. Redraw the circuit of Question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12
,
Omega resistor. What would be the readings in the ammeter and the voltmeter? Answer Q1 1. Judge the equivalent resistance when the following are connected in parallel – (a) 1
,
Omega and 10
6
,
Omega, (b) 1
,
Omega and 10
3
,
Omega, and 10
6
,
Omega. Answer Q2 2. An electric lamp of 100
,
Omega, a toaster of resistance 50
,
Omega, and a water filter of resistance 500
,
Omega are connected in parallel to a 220
,
mathrmV source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it? Answer Q3 3. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series? Answer Q4 4. How can three resistors of resistances 2
,
Omega, 3
,
Omega, and 6
,
Omega be connected to give a total resistance of (a) 4
,
Omega, (b) 1
,
Omega? Answer Q5 5. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4
,
Omega, 8
,
Omega, 12
,
Omega, 24
,
Omega? Answer Q1 1. Why does the cord of an electric heater not glow while the heating element does? Answer Q2 2. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50
,
mathrmV. Answer Q3 3. An electric iron of resistance 20
,
Omega takes a current of 5
,
mathrmA. Calculate the heat developed in 30
,
mathrms. Answer Q1 1. What determines the rate at which energy is delivered by a current? Answer Q2 2. An electric motor takes 5
,
mathrmA from a 220
,
mathrmV line. Determine the power of the motor and the energy consumed in 2
,
mathrmh. Answer Q1 1. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R′, then the ratio R/R′ is – (a) 1/25 (b) 1/5 (c) 5 (d) 25 Answer Q2 2. Which of the following terms does not represent electrical power in a circuit? (a) I
2
R (b) IR
2
(c) VI (d) V
2
/R Answer Q3 3. An electric bulb is rated 220
,
mathrmV and 100
,
mathrmW. When it is operated on 110
,
mathrmV, the power consumed will be – (a) 100
,
mathrmW (b) 75
,
mathrmW (c) 50
,
mathrmW (d) 25
,
mathrmW Answer Q4 4. Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be – (a) 1:2 (b) 2:1 (c) 1:4 (d) 4:1 Answer Q5 5. How is a voltmeter connected in the circuit to measure the potential difference between two points? Answer Q6 6. A copper wire has diameter 0.5
,
mathrmmm and resistivity of 1.6
times10
−8
,
Omega
,
mathrmm. What will be the length of this wire to make its resistance 10
,
Omega? How much does the resistance change if the diameter is doubled? Answer Q7 7. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below – I
(
mathrmamperes)
quad0.5
quad1.0
quad2.0
quad3.0
quad4.0 V
(
mathrmvolts)
quad1.6
quad3.4
quad6.7
quad10.2
quad13.2 Plot a graph between V and I and calculate the resistance of that resistor. Answer Q8 8. When a 12
,
mathrmV battery is connected across an unknown resistor, there is a current of 2.5
,
mathrmmA in the circuit. Find the value of the resistance of the resistor. Answer Q9 9. A battery of 9
,
mathrmV is connected in series with resistors of 0.2
,
Omega, 0.3
,
Omega, 0.4
,
Omega, 0.5
,
Omega and 12
,
Omega, respectively. How much current would flow through the 12
,
Omega resistor? Answer Q10 10. How many 176
,
Omega resistors (in parallel) are required to carry 5
,
mathrmA on a 220
,
mathrmV line? Answer Q11 11. Show how you would connect three resistors, each of resistance 6
,
Omega, so that the combination has a resistance of (i) 9
,
Omega, (ii) 4
,
Omega. Answer Q12 12. Several electric bulbs designed to be used on a 220
,
mathrmV electric supply line, are rated 10
,
mathrmW. How many lamps can be connected in parallel with each other across the two wires of 220
,
mathrmV line if the maximum allowable current is 5
,
mathrmA? Answer Q13 13. A hot plate of an electric oven connected to a 220
,
mathrmV line has two resistance coils A and B, each of 24
,
Omega resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases? Answer Q14 14. Compare the power used in the 2
,
Omega resistor in each of the following circuits: (i) a 6
,
mathrmV battery in series with 1
,
Omega and 2
,
Omega resistors, and (ii) a 4
,
mathrmV battery in parallel with 12
,
Omega and 2
,
Omega resistors. Answer Q15 15. Two lamps, one rated 100
,
mathrmW at 220
,
mathrmV, and the other 60
,
mathrmW at 220
,
mathrmV, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220
,
mathrmV? Answer Q16 16. Which uses more energy, a 250
,
mathrmW TV set in 1
,
mathrmhr, or a 1200
,
mathrmW toaster in 10 minutes? Answer Q17 17. An electric heater of resistance 44
,
Omega draws 5
,
mathrmA from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater. Answer Q18 18. Explain the following. (a) Why is the tungsten used almost exclusively for filament of electric lamps? Answer Q19 (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? Answer Q20 (c) Why is the series arrangement not used for domestic circuits? Answer Q21 (d) How does the resistance of a wire vary with its area of cross-section? Answer Q22 (e) Why are copper and aluminium wires usually employed for electricity transmission? Answer
Ohm’s law is expressed as:
A R = VI B V = IR C V = I/R D I = VR
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