electricity class 10 cbse

S.No.	Electricity class 10
	Intext questions page 200
1	What does an electric circuit mean?
2	Define the unit of current.
3	Calculate the number of electrons constituting one coulomb of charge
	Intext questions page 202
1	Name a device that helps to maintain a potential difference across aconductor.
2	What is meant by saying that the potential difference between two pointsis 1 V?
3	How much energy is given to each coulomb of charge passing through a6 V battery?
	Intext questions page 209
1	On what factors does the resistance of a conductor depend?
2	Will current flow more easily through a thick wire or a thin wire of thesame material, when connected to the same source? Why?
3	Let the resistance of an electrical component remains constant whilethe potential difference across the two ends of the component decreasesto half of its former value. What change will occur in the current throughit?
4	Why are coils of electric toasters and electric irons made of an alloyrather than a pure metal?
5	Use the data in Table 12.2 to answer the following –(a) Which among iron and mercury is a better conductor?(b) Which material is the best conductor?
	Intext questions page 213 ( electricity class 10 cbse )
1	Draw a schematic diagram of a circuit consisting of a battery of threecells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, anda plug key, all connected in series.
2	Redraw the circuit of Question 1, putting in an ammeter to measurethe current through the resistors and a voltmeter to measure thepotential difference across the 12 Ω resistor. What would be the readingsin the ammeter and the voltmeter?
	Intext questions page 216  ( electricity class 10 cbse )
1	Judge the equivalent resistance when the following are connected inparallel – (a) 1 Ω and 106 Ω, (b) 1 Ω and 103 Ω, and 106 Ω
2	An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filterof resistance 500 Ω are connected in parallel to a 220 V source. What isthe resistance of an electric iron connected to the same source thattakes as much current as all three appliances, and what is the currentthrough it?
3	What are the advantages of connecting electrical devices in parallelwith the battery instead of connecting them in series?
4	How can three resistors of resistances 2 Ω, 3 Ω, and 6 Ω be connected togive a total resistance of (a) 4 Ω, (b) 1 Ω?
5	What is (a) the highest, (b) the lowest total resistance that can be securedby combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?
	Intext questions page 218  ( electricity class 10 cbse )
1	Why does the cord of an electric heater not glow while the heating elementdoes?
2	Compute the heat generated while transferring 96000 coulomb of chargein one hour through a potential difference of 50 V.
3	An electric iron of resistance 20 Ω takes a current of 5 A. Calculate theheat developed in 30 s.
	Intext questions page 220  ( electricity class 10 cbse )
1	What determines the rate at which energy is delivered by a current?
2	An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.
	EXERCISES  ( electricity class 10 )
1	A piece of wire of resistance R is cut into five equal parts. These parts are thenconnected in parallel. If the equivalent resistance of this combination is R′, then theratio R/R′ is –(a) 1/25 (b) 1/5 (c) 5 (d) 25
2	Which of the following terms does not represent electrical power in a circuit?(a) I2R (b) IR2 (c) VI (d) V2/R
3	An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, thepower consumed will be –(a) 100 W (b) 75 W (c) 50 W (d) 25 W
4	Two conducting wires of the same material and of equal lengths and equal diametersare first connected in series and then parallel in a circuit across the same potentialdifference. The ratio of heat produced in series and parallel combinations would be –(a) 1:2 (b) 2:1 (c) 1:4 (d) 4:1
5	How is a voltmeter connected in the circuit to measure the potential differencebetween two points?
6	A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10–8 Ω m. What will bethe length of this wire to make its resistance 10 Ω? How much does the resistancechange if the diameter is doubled?
7	The values of current I flowing in a given resistor for the corresponding values ofpotential difference V across the resistor are given below –I (amperes) 0.5 1.0 2.0 3.0 4.0V (volts) 1.6 3.4 6.7 10.2 13.2Plot a graph between V and I and calculate the resistance of that resistor.
8	When a 12 V battery is connected across an unknown resistor, there is a current of2.5 mA in the circuit. Find the value of the resistance of the resistor.
9	A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω , 0.5 Ωand 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
10	How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
11	Show how you would connect three resistors, each of resistance 6 Ω, so that thecombination has a resistance of (i) 9 Ω, (ii) 4 Ω.
12	Several electric bulbs designed to be used on a 220 V electric supply line, are rated10 W. How many lamps can be connected in parallel with each other across the twowires of 220 V line if the maximum allowable current is 5 A?
13	A hot plate of an electric oven connected to a 220 V line has two resistance coils Aand B, each of 24 Ω resistance, which may be used separately, in series, or inparallel. What are the currents in the three cases?
14	Compare the power used in the 2 Ω resistor in each of the following circuits:(i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallelwith 12 Ω and 2 Ω resistors.
15	Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connectedin parallel to electric mains supply. What current is drawn from the line if the supplyvoltage is 220 V?
16	Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
17	An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours.Calculate the rate at which heat is developed in the heater
18	Explain the following.(a) Why is the tungsten used almost exclusively for filament of electric lamps?(b) Why are the conductors of electric heating devices, such as bread-toastersand electric irons, made of an alloy rather than a pure metal?(c) Why is the series arrangement not used for domestic circuits?(d) How does the resistance of a wire vary with its area of cross-section?(e) Why are copper and aluminium wires usually employed for electricitytransmission?