CBSE Class 10 Science Chapter-12 Electricity – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 10 Science Chapter 12 – Electricity prepared by expert Science teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 10 Science Chapter-12 Electricity Important Questions
CBSE Class 10 science Important Questions Chapter 12 – Electricity
2 Mark Questions
1. How does use of fuse wire protect electrical appliances?
Ans. When large amount of current flows through the circuit, temperature of the wire increases and fuse wire gets melted. This in term prevent the flow of current in the other circuits of the house and thus saved electrical appliances.
2. Calculate the resistance of an electric bulb which allows a 10A current when connected to a 220V power source?
Ans. I=10A, V=220V
R=
= 
=22 ohm
3. (i) Identify the V-I graphs for ohmic and non-ohmic materials.
(ii) Give one example of each.
Ans. (i)(a) Ohmic material
(b) Non-ohmic material
(ii) Example of ohmic material – Copper, Nichrome etc.
Example of Non-ohmic material –Diode, Transistor etc.
4. What do the following symbols represent in a circuit?
Write the name and one function of each?
Ans. (i) 
It represents a battery which maintains a potential difference across the circuit element for the flow of current in the circuit.
(ii) 
It is an ammeter which measures the current flowing in the circuit.
5. Define the term “volt”?
Ans. The potential difference between two points A and B is said to be one volt if 1 joule of work is done to move 1 coulomb of charge from one point to another point in an electric field.
6. Why does the connecting rod of an electric heater not glow while the heating element does?
Ans. The connecting cord of an electric heater does not glow because its resistance is less as compared to the heating element. Hence more heat is produced is the heating element as compared to the connecting cord and it glows.
7. n resistors each of resistance R are first connected in series and then in parallel. What is the ratio of the total effective resistance of the circuit is series combination and parallel combination?
Ans. In series combination Rs=nR
For parallel Rp=
8. Draw a schematic diagram of a circuit consisting of 3V battery, 5 ohm, 3 
and 1resistor, an ammeter and a plug key, all connected in series.
Ans.
9. A copper wire has diameter 0.5mm and Resistivity of 
what be the length of this wire to make its resistance
? How much does the resistance change if diameter is doubled?
Ans. D= 0.5 mm = 0.5
m
P= 1.6210-8 
R= 10
Length of the wire, l=121.14m
10. Alloys are used in electrical heating devices rather than pure metals. Give reason.
Ans. Alloys are used in electricity heating devices rather than pure metals because Resistivity of an alloy is more and hence more heat is produced in any alloy. Moreover, alloy does not burn (or oxidize easily at higher temperature).
11. On what factor does the resistance of a conductor depend?
Ans. Resistance depends on the following factors
(1) R 
l (length of the conductor)
(2) R l/A (area of cross – section)
(3) R t (temperature)
(4) R depends on nature of material.
12. Calculate the number of electron consisting one coulomb of charge?
Ans. q 1e
x = no. of electrons
Since = n e
x = q/e = 
13. What does an electric circuit mean?
Ans. An electric circuit is a continuous and closed path of an electric current. If the electric circuit complete, current can flow through the circuit.
14. Define the unit of current.
Ans. SI unit of electric current is Ampere. Current is said to be 1 ampere, if 1 coulomb charge flows per second across a cross-section of conductor.
15. Calculate the number of electrons constituting one coulomb of charge.
Ans. Charge on one electron 
coulomb.
No of electron in one coulomb of charge = 
16. What is meant by saying that the potential difference between two points is 1 v?
Ans. The potential difference between two points is said to be 1 volt, if 1 joule of work is to be done for moving charge of 1 coulomb from one point to another.
17. Ammeter burns out when connected in parallel. Give reasons.
Ans. Ammeter consists of a wire of low resistance when connected in parallel, a large amount of current passes though it hence gets burnt i.e. short circuited.
18. Judge the equivalent resistance when the following are connected in parallel:
(a) 1 Ω and 106 Ω
(b) 1 Ω, 103 Ω and 106 Ω
Ans. When the resistances are joined in parallel, the resultant resistance in parallel arrangement is given by:
(a) 
R = 1Ω
(b) 
R= 1Ω
19. An electric iron of resistance 20 takes a current of 5 A. Calculate the heat developed in 30 s.
Ans. Resistance of electric iron (R) = 20Ω, current (I) = 5 A and time = 30 s.
Heat generated 
= 15000j.
20. Compute the heat generated while transferring 96000 coulomb of charge in one hour
through a potential difference of 50 V.
Ans. Charge transferred (Q) = 96000 C, time = 1 hour = 
and potential difference (V)= 50 V.
Heat generated (H) = VIt = V.Q = 
= 4800000 j =
.
21. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and energy consumed in 2 h.
Ans. It is given that current drawn by electric motor (I) = 5 A. the line voltage V = 220 V time (t) = 2
h. Power of motor (P) = P = VI 
= 1100 W and the energy consumed 
= 2200 Wh or 2.2kWh.
22. How is a voltmeter connected in the circuit to measure the potential difference between two points?
Ans. A voltmeter is always connected in parallel to resistance across the point between which the potential difference is to be measured.
23. When a 12 v battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
Ans. Voltage of battery = V = 12 V, Current (I) = 2.5 mA 
Resistance (R) = V/I 
= 4800 Ω.
24. Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220V line if the maximum allowable current is 5 A?
Ans. Each bulb is rated as 10 W, 220 V, It draws a current (I) = P/V = 10W/220 V= 1/22 A.
As the maximum allowable current is 5A and all lamps are connected in parallel, hence maximum number of bulbs joined in parallel with each other
.
25. 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?
Ans. Current drawn by 1st lamp rated 100 W at 220 V = P/V = 100/ 220 = 5/11 A.
Current drawn by 2nd lamp rated 60 W at 220 V = 60/220 = 3/11 A.
In parallel arrangement the total current = I1 +I2 = 3/11+ 5/11 = 8/11 = 0.73 A.
26. Which uses more energy, a 250 W TV set in 1 hour, or a 1200 W toaster in 10 minutes?
Ans. Energy used by a TV set of power 250 W in 1 hour =
.
Energy used by toaster of power 1200 W in 10 minute (10/60 h)
= 200 Wh.
27. An electric heater of resistance 8 draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater.
Ans. Resistance of electric heater (R) = 8Ω, current (I) = 15 A.
Rate at which heat developed in the heater 
= 1800 W.
28. In the given figure what is the ratio of current in A
Ans. V=IR
V=const.
29. Two wires of equal cross sectional area, one of copper and other of managing have same resistance. Which one will be longer?
Ans.
P manganin > P copper
L copper > L manganin
30. A Rectangular block of iron has dimensions LX LX b. What is the resistance of the block measured between the two square ends? Given p resistivity.
Ans. 
31. Three equal resistances are connected in series then in parallel. What will be the ratio of their Resistances?
Ans. 
32. Justify for any pair of resistance the equivalent resistance equivalent resistance in parallel.
Ans. Since, RV/I
A=Series, B=Parallel
33. How many bulbs of 81 should be joined in parallel to draw a current of 2A from a battery of 4 V?
Ans. 
let ‘n’ battery of bulbs.
34. Two cubes A and B are of the same material. The side of B is thrice as that of A. Find the ratio RA/RB.
Ans. 
35. 
electrons are flowing through the filament of bulb for two minutes. Find owing through the circuit. Charge on one electron
.
Ans. 
36. A nichrome wire of resistivity l00XlW m and copper wire of resistivity 1.62M ohm-m of same length and same area of cross section are connected in series , current is passed through them, why does the nichrome wire gets heated first?
Ans. 
Nichrome wire has higher resistivity than copper wire Therefore, it is heated first.
37. What is represented by joule/coulomb?
Ans. It represents potential difference.
38. A charge of 2C moves between two plates, maintained at a p.d of IV. What is the energy acquired by the charge?
Ans. 
The resistance of a voltmeter is very high and for an ideal voltmeter, its value is infinity.
39. Which has more resistance: 100W bulb or 60W bulb?
Ans. As Ra 1/P. Thus, the resistance of 60W bulb is more.
40. What happens to the current in a circuit if its resistance is doubled?
Ans. MI a I/It, the current is reduced to half of its previous value.
41. What happens to the resistance of a circuit if the current through it is doubled?
Ans. The resistance of the circuit does not depend on the current through it.
42. How does the resistance of a wire depend upon its radius?
Ans. As R a 1/A, R a 1/ i.e. R a v
43. Two wires are of the same length, same radius, but one of them is of copper and the other is of iron. Which will have more resistance.
Ans. As R = p1/A, but A and I are same it depends only on resistivity and it is more for iron so iron has more resistance.
44. Two wires of same material and same length have radii r and r Compare their resistances.
Ans. If R and It are resistances, then R = r because p and I are same.
