Page No 202:
Question 2:
What is meant by saying that the potential difference between two points is 1 V?
Page No 202:
Question 3:
How much energy is given to each coulomb of charge passing through a 6 V battery?
Page No 209:
Question 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?
Page No 209:
Question 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?
Page No 209:
Question 4:
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Page No 209:
Question 5:
Use the data in Table 12.2 to answer the following −
Table 12.2 Electrical resistivity of some substances at 20°C
− | Material | Resistivity (Ω m) |
Conductors | Silver | 1.60 × 10−8 |
Copper | 1.62 × 10−8 | |
Aluminium | 2.63 × 10−8 | |
Tungsten | 5.20 × 10−8 | |
Nickel | 6.84 × 10−8 | |
Iron | 10.0 × 10−8 | |
Chromium | 12.9 × 10−8 | |
Mercury | 94.0 × 10−8 | |
Manganese | 1.84 × 10−6 | |
Constantan (alloy of Cu and Ni) | 49 × 10−6 | |
Alloys | Manganin (alloy of Cu, Mn and Ni) | 44 × 10−6 |
Nichrome (alloy of Ni, Cr, Mn and Fe) | 100 × 10−6 | |
Glass | 1010 − 1014 | |
Insulators | Hard rubber | 1013 − 1016 |
Ebonite | 1015 − 1017 | |
Diamond | 1012 − 1013 | |
Paper (dry) | 1012 |
(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?
Page No 213:
Question 2:
Redraw the circuit of question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure potential difference across the 12 Ω resistor. What would be the readings in the ammeter and the voltmeter?
Page No 216:
Question 2:
An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V 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?
Page No 216:
Question 3:
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
Page No 216:
Question 4:
How can three resistors of resistances 2 Ω, 3 Ω and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω?
Page No 216:
Question 5:
What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?
Page No 218:
Question 1:
Why does the cord of an electric heater not glow while the heating element does?
Page No 221:
Question 5:
How is a voltmeter connected in the circuit to measure the potential difference between two points?
Page No 221:
Question 6:
A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10−8 Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?
Page No 221:
Question 9:
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
Page No 221:
Question 10:
How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
Page No 221:
Question 12:
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 220 V line if the maximum allowable current is 5 A?
Page No 221:
Question 13:
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistances, which may be used separately, in series, or in parallel. What are the currents in the three cases?
Page No 221:
Question 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 parallel with 12 Ω and 2 Ω resistors.
Page No 222:
Question 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?
Page No 222:
Question 16:
Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
Page No 222:
Question 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-toasters and 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 electricity transmission?
Page No 221:
Question 2:
Which of the following terms does not represent electrical power in a circuit?
