NCERT solutions for class 10 science chapter 12 Electricity: While doing preparation for class 10 board exams, you must know that chapter 12 Electricity is one of the most important chapters. This is a scoring chapter and also very useful when you go to class 12. So it will be good for you if you clear your concepts in class 10 itself. The solutions of NCERT for class 10 science chapter 12 Electricity will help you understand that electrical energy is one of the major forms of energy that we are using in our daily lives. One of the important features of electric energy is that it can be transmitted to a large distance with very little power loss. The electrical energy is obtained from various sources such as water, steam, and nuclear energy, etc.
In the CBSE NCERT solutions for class 10 science chapter, 12 Electricity questions related to direct current are discussed. Direct current is unidirectional current whereas the alternating current changes its direction periodically. The measurement of the current is done with the help of ammeter and voltage with the help of a voltmeter. Another important topic that you can understand with the help of solutions for NCERT class 10 science chapter 12 Electricity is a combination of resistors in series and parallel. The main aim of NCERT solutions for class 10 science chapter 12 Electricity is to give a better knowledge of how to use the concept while answering the questions. The NCERT solutions will help you score well in the CBSE board exam.
The solutions of NCERT class 10 science chapter 12 electricity deal with the questions related to the concept of:
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Certain points to remember from solutions for class 10 science chapter 12 electricity for NCERT
Topic 12.1 Electric Current and Circuit
Q.1 What does an electric circuit mean?
Answer:
A closed and continuous path of electric current is known as the electric circuit. It consists of electric circuit elements like battery, resistors etc and electric devices like a switch and measuring devices like ammeters etc.
Q.2 Define the unit of current.
Answer:
Ampere(A) is unit of current.1A is flow of 1C of charge through a wire in 1s of time.
Q.3 Calculate the number of electrons constituting one coulomb of charge.
Answer:
Given: Q=1C
We know that the charge of an electron
Thus, the number of electrons constituting one coulomb of charge is electrons.
Topic 12.2 Electric Potential and Potential Difference
Q.1 Name a device that helps to maintain a potential difference across a conductor.
Answer:
Battery, cell or power supply source helps to maintain a potential difference across a conductor.
Q.2 What is meant by saying that the potential difference between two points is 1 V?
Answer:
The potential difference between two points is 1 V means 1 J of work is required to move a charge of amount 1C from one point to another.
Q.3 How much energy is given to each coulomb of charge passing through a 6 V battery?
Answer:
Given : potential difference = 6V and carge =1C.
J
Thus, 6J energy is given to each coulomb of charge passing through a 6 V battery.
Topic 12.5 Factors on which the resistance of a conductor depends
Q.1 On what factors does the resistance of a conductor depend?
Answer:
The resistance of a conductor depends on :
1. Cross section area of the conductor.
2.length of conductor
3.The temperature of the conductor.
4. Nature of material of the conductor.
Answer:
We know that resistance is given as
R=resistance
=resistivity
l=length of wire
A=area of cross section
Resistance is inversely proportional to the area of cross-section.
Thicker the wire more is cross-sectional area resulting in less resistance resulting in more current flow.
Answer:
By Ohm's law,
V=IR
V= potential difference
I =current
R = resistance
Now, the potential difference is reduced to half i.e.
R' = R=resistance
I' =current
Current flowing is reduced to half.
Q.4 Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Answer:
The resistivity of an alloy is higher than pure metal so alloy does not melt at high temperature. Thus, coils of electric toasters and electric irons made of an alloy rather than a pure metal.
Q.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?
Answer:
Lower the value of resistivity lower will be the resistance for a material of given area and length. If resistance is law current flow will be high when a potential difference is applied across the conductor.
(a).resistivity of iron =
the resistivity of mercury =
the resistivity of mercury is more than iron so iron is a better conductor than mercury.
(b).From the table, we can observe silver has the lowest resistivity so it is the best conductor.
Topic 12.6 Resistance of a system of resistors
Answer:
The schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a resistor, an resistor, and a resistor, and a plug key, all connected in series is as shown below :
Answer:
The diagram is as shown :
Resistance of circuit =R=5+8+12=25
Potential = 6V
Now, for 12 ohm resistor, current = 0.24 A.
By Ohm's law,
The reading of the ammeter is o.24A and the voltmeter is 2.88V.
Topic 12.6.2 Resistors in Parallel
Q.1 Judge the equivalent resistance when the following are connected in parallel –
Answer:
R=Equivalent resistance
R=Equivalent resistance
Answer:
Given :
R=Equivalent resistance
By Ohm's law,
Hence, the resistance of electric iron is 31.25 and current through it is 7.04A.
Answer:
In parallel, there is no division of voltage among the appliances so the potential difference across all appliance is equal and the total effective resistance of a circuit can be reduced. Hence, connecting electrical devices in parallel with the battery is beneficial instead of connecting them in series.
Q.4 How can three resistors of resistances be connected to give a total resistance of
Answer:
(a)
R=Equivalent resistance
(b).1 Ohm
R=Equivalent resistance
Connect all the three resistors in parallel
Answer:
(a) the highest total resistance is obtained when all the resistors are connected in series
Answer:
(b) the lowest total resistance is R is obtained when all the resistors are connected in parallel.
Q. 1. Why does the cord of an electric heater not glow while the heating element does?
Answer:
The heating element of an electric heater is a resistor.
The amount of heat production is given as , .
The resistance of elements (alloys) of an electric heater is high. As current flow through this element, it becomes hot and glows red.
The resistance of cord (metal like Cu or Al)of an electric heater is low. As current flow through this element, it does not becomes hot and does not glow red.
Answer:
Given : potential difference = 50 V.
Charge = 9600 C
time = 1 hr=3600 s
So,
Q.3 An electric iron of resistance takes a current of 5 A. Calculate the heat developed in 30 s.
Answer:
Given : resistance=R= , TIME =30s , current =I=5A
Topic 12.8 Electric power
Answer:
The rate at which energy is delivered by a current is power.
Power P=I^{2}R, where I is the current and R is the resistance of the circuit/ appliance. Power depends on the current drawn by the appliance and the resistance of the appliance.
Answer:
Given: I= 5 A and V= 220 V.
Power=P=VI
Time = 2hr=
The energy consumed =
Power of motor = 1100W
Energy consumed by motor = 7920000J
NCERT solutions for class 10 science chapter 12 Electricity- Exercise solutions
Answer:
Given: A piece of wire of resistance is cut into five equal parts.
Resistance of each part is .
Hence,
Thus, option D is correct.
Q. 2. Which of the following terms does not represent electrical power in a circuit?
Answer:
We know that power = P=VI....................................1
Put , V=IR in equation 1
Pur , in equation 1,
P= power, V=potencial difference, I= current,R=resistance
P cannot be .
Thus, option B is correct.
Q. 3. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be
(a) 100 W (b) 75 W (c) 50 W (d) 25 W
Answer:
Given : V=220V,P=100W
The resistance of the bulb
If bulb is operated on 110 Vand resistance is the same , the power consumed will be P'
Hence, option D is correct.
(a) 1:2 (b) 2:1 (c) 1:4 (d) 4:1
Answer:
If resistors are connected in parallel, the net resistance is given as
If resistors are connected in series, the net resistance is given as
Heat produced = H =
Thus, option C is correct.
Q. 5. How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer:
A voltmeter should be connected in parallel, to measure the potential difference between two points.
Answer:
Given : diameter=d= 0.5 mm and resistivity = = m.,resistance =R=10
Area =A
We know
If the diameter is doubled.
d=1 mm
Area =A'
We know
Hence, new resistance is of original resistance.
Q. 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 (amperes) 0.5 1.0 2.0 3.0 4.0
V (volts) 1.6 3.4 6.7 10.2 13.2
Plot a graph between V and I and calculate the resistance of that resistor
Answer:
The plot between voltage and current is as shown :
The slope of the line gives resistance (R)
Answer:
Given : V=12V , I = 2.5 mA = 0.0025 A
Answer:
Total resistance =R
V = 9V
Hence, All resistors are in series so 0.67A current would flow through the resistor.
Q.10. How many resistors (in parallel) are required to carry 5 A on a 220 V line?
Answer:
Given: V=220V and I =5A
Let x number of resistors are connected in parallel to obtain 44 Ohm equivalent resistance.
Thus,
Hence, 4 resistors of 176 Ohm are connected in parallel to obtain 44 Ohm.
Answer:
(i)
R=Equivalent resistance
(ii)
.
R=Equivalent resistance
Answer:
Given: V=220V and P=10W
Let x be the number of bulbs.
I = 5A and V=220V
For x bulbs of resistance 4680 Ohm, are connected in parallel to obtain 44 Ohm equivalent resistance.
Thus,
Hence, 110 bulbs of 4840 Ohm are connected in parallel to obtain 44 Ohm.
Q.13. A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
Answer:
Given : V=220V and Resistance of each coil=R =24A
When coil is used separately,current in coil is
When two coils are connected in series, net resistance is
current in coil is I'
When two coils are connected in parallel, net resistance is
current in the coil is I''
Q.14. Compare the power used in the resistor in each of the following circuits:
(i) a 6 V battery in series with and resistors
(ii) a 4 V battery in parallel with and resistors.
Answer:
i) Given: V=6V
R=1+2=3Ohm
In, a series current is constant.
So, power =P
ii) Given: V=6V , R=2 Ohm
In, parallel combination voltage in the circuit is constant.
So, power =P
Answer:
Given :
For lamp one: Power = P1=100W and V = 220V
For lamp two: Power = P2=60W and V = 220V
Thus, the net current drawn from the supply is 0.455+0.273=0.728A
Q.16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
Answer:
For TV set :
Given : Power = 250W and time = 1 hr = 3600 seconds
Energy consumed = H=PI
For toaster :
Given : Power = 1200W and time = 10 minutes = 600 seconds
Energy consumed = H=PI
Thus, the TV set uses more energy than a toaster.
Answer:
Given: R=8 Ohm ,I=15A and t= 2hr
The heat developed in the heater is H.
The rate at which heat is developed is given as
Q.18(a). Explain the following.
(a) Why is the tungsten used almost exclusively for filament of electric lamps?
Answer:
The tungsten used almost exclusively for filament of electric lamps because the melting point of tungsten is very high. The bulb glows at a very high temperature. So tungsten filament does not melt when bulb glows.
Q.18.(b) Explain the following.
Answer:
The conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal because the resistivity of the alloy is more than a pure metal. So the resistance will be hight and the heating effect will be high.
Q.18.(c) Explain the following.
(c) Why is the series arrangement not used for domestic circuits?
Answer:
If any of the elements in the circuit get damaged the entire circuit will be affected. If an element brake there will not be any current flow through the circuit. So the series circuit is not preferred in the domestic circuit.
Q.18.(d) Explain the following.
(d) How does the resistance of a wire vary with its area of cross-section?
Answer:
We know that
Thus, the resistance of a wire is inversely proportional to its area of cross-section.
Q.18.(e) Explain the following.
(e) Why are copper and aluminium wires usually employed for electricity transmission?
Answer:
Copper and aluminium wires usually employed for electricity transmission because they have low resistivity and they are good conductors of electricity.
What is meant by saying that the potential difference between two points is 1 V?
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
Q.15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?