2. 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.
3. Calculate the number of electrons constituting one coulomb of charge.
Ans. Charge on one electron = 1.6 x 10-19coulomb.
No of electron in one coulomb of charge = 1/1.6 x 10-19 = 6.25 x 1018 electrons.
Page No. 202
1. Name a device that helps to maintain a potential difference between across a conductor.
Ans. Battery
2. 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.
3. How much energy is given to each coulomb of charge passing through a 6-volt battery?
Ans. Potential difference (V) = 6 V
Charge (Q) = 1 C
Energy = total work done (W) = Q x V = 1x6 = 6 joule.
Page No. 209
1. On what factor does the resistance of a conductor depend?
Ans. The resistance of a conductor depends on
i. length of conductor (l)
ii. Area of cross-section (A)
iii. Temperature
iv. Nature of material used to make conductor
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?
Ans. The current flows more easily through a thick wire as compared to thin wire of the same material, when connected to the same source. It is due to the reason that resistance increases with decrease in thickness.
3. Let the resistance of an electric 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. It is given that resistance R of the electrical component remains constant but the potential difference across the ends of the component decreases to half of its value.
Hence, as per Ohm’s law, new current also decreases to half of its original value.
4. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Ans. Coils of electric toasters and electric irons are made of an alloy due to the following reasons:
i. Resistivity of an alloy is generally higher than that of pure metal.
ii. At high temperature, an alloy does not oxidize readily. Hence, coil of an alloy has longer life.
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?
Ans. (a) Iron is the better conductor than mercury.
(b) Silver is the best conductor because its resistivity is the least.
Page No. 213
1. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V, each, a 5 Ώ resistor, 8 Ώ resistors and a 12 Ώ and a plug key, all connected in series.
Ans. The schematic diagram of circuit is as follows:

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 Ώ resistors. What would be the reading in the ammeter and voltmeter?
Ans.

Here ammeter A has been joined in series of circuit and voltmeter V is joined in parallel to 12 ohms’ resistor.
Total voltage of battery V = 3x2 = 6 V.
Total resistance R = R1+ R2+ R3 = 5 Ω +8 Ω +12 Ω = 25 Ω
Ammeter reading (current) = I = V/R = 6/25 = 0.24 A.
Voltmeter reading = IR = 0.24 x 12 = 2.88 V.
Posted by Rishabh Pawar
5 years, 1 month ago
Test
King Adithya H M... 5 years, 1 month ago
0Thank You