Which of the following are conductors and which are insulators?
Sulphur, Silver, Copper, Cotton, Aluminium, Air, Nichrome, Graphite, Paper, porcelain, Mercury, Mica, Bakelite, Polythene, Manganin.
The figure blow shows a variable resistor in a dimmer switch.
How would you turn the switch to make the lights: (a) brighter, and (b) dimmer? Explain your answer.
Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be –
Give two examples of substances which are good conductors of electricity. Why do you think they are good conductors of electricity?
Classify the following into good conductors, resistors and insulators:
Rubber, Mercury, Nichrome, Polythene, Aluminium, Wood, Manganin, Bakelite, Iron, Paper, Thermocol, Metal coin
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?
Calculate the area of cross-section of a wire if its length is 1.0 m, its resistance is 23 Ω and the resistivity of the material of the wire is 1.84 × 10−6 Ω m.
A wire is 1.0 m long, 0.2 mm in diameter and has a resistance of 10 Ω. Calculate the resistivity of its material?
Calculate the resistance of a copper wire 1.0 km long and 0.50 mm diameter if the resistivity of copper is 1.7 × 10−8 Ω m.
A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10−8Ω 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?
Which has less electrical resistance : a thin wire or a thick wire (of the same length and same material)?
Fill in the following blanks with suitable words:
Copper is a good .......... Plastic is an ..........
Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistance and two insulators.
What is meant by the "resistance of a conductor" ? Write the relation between resistance, potential difference and current.
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|
(alloy of Cu and Ni)
|49 × 10−6|
(alloy of Cu, Mn and Ni)
|44 × 10−6|
(alloy of Ni, Cr, Mn and Fe)
|100 × 10−6|
|Glass||1010 − 1014|
|Insulators||Hard rubber||1013 − 1016|
|Ebonite||1015 − 1017|
|Diamond||1012 − 1013|
What will be the resistance of a metal wire of length 2 metres and area of cross-section 1.55 × 10−6 m2 if the resistivity of the metal be 2.8 × 10−8 Ω m?