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Current Electricity (Assignment-I) 1. A copper wire of area of cross-section 2.09 x 10-12 sq cm carries a current of 1 amp. Calculate current density. [4.784 x 105 A/m2] 2. There is a wire of resistance 100 Ω. What is the resistance of another wire of same material but length and radius respectively twice and half of the first wire? [800Ω] 3. Calculate the resistance of a hollow cylinder of inner and outer radius respectively 0.2 m and 0.3 m. The length of the cylinder is 3.4 m and its specific resistance is 2 x 10-8 Ω-m. [0.4 µΩ] 4. In a neon gas discharge tube 2.98 x 1018 Ne+ ion move to the right through a cross-section of the tube each second, while 1.2 x 1019 electrons move to the left in the same time. Find the magnitude of the current. [2.384 A] 5. A metal wire of diameter 2 mm and of length 100 mm has a resistance of 0.545 Ω at 20° C and 0.805 Ω at 150°C. Find the value of temperature co-efficient of resistance. [3.9 x 10-3 °C-1] 6. A wire having a mass of 0.45 kg possesses resistance of 0.14 Ω. If the resistivity of the material of the wire is 1.78 x 10-8 ohm-m, calculate its length and radius. Given that density of material of wire is 8.93x10 3 kg/m3. [8.9 x10-4 m] 7. A wire of resistance 5 ohm is drawn, so that its length is increased to twice its original length. Calculate its new resistance. [20 ohm] 8. The resistance of a conductor is 6 Ω at 50° C and 7 Ω at 100° C. Find its resistance at 0°C. [5 Ω] 9. Compare the resistance of two wires of same material. Their lengths are in the ratio of 2:3 & their diameters are in the ratio of 1:2. [8:3] 10. A given wire of resistance R is stretched so as to reduce its diameter to half its previous value. What will be its new value? [16R] 11. When a current i is flowing thro’ a conductor, the drift velocity is v. If 2i current is flowed thro’ the same metal but having double the area of cross-section, then the drift velocity will be…….??? [v] 12. A wire of diameter 0.02 m contains 1028 free electrons/cubic meter. For an electric current of 1 A, the drift velocity of the free electrons is nearly……..???? [2 x 10-4 m/s] 13. When the length & area of cross-section of a wire are doubled, then its resistance is……?? [remains same] 14. The resistivity of a wire is ρ. Its volume is 3 m 3 and its resistance is 3 Ω, then its length will be..? [3/√ρ] 15. Resistance of tungsten wire at 150°C is 133 Ω. Its resistance temperature co -efficient is 0.0045 °C-1. The resistance of the wire at 500 °C is …??? [258 ohm] 16. The conductivity of superconductor is …….?? [ infinite ] 17. Two wires A and B of same material & same mass have radius 2r and r. If the resistance of wire A is 34 Ω, what will be the resistance of wire B? [544 Ω] 18. A nichrome wire 50 m long and 1 sq mm cross-section area carries a current of 4A when connected to a 2V battery. Find the resistivity of nichrome wire. [1 x10-8 Ω-m] 19. The length of resistance wire is increased by 10%. What is the corresponding change in the resistance of the wire? [21%] 20. Two wires that are made up of two different materials whose resistivity are in the ratio 2:3 and length 3:4 and area 4:5. The ratio of their resistances is…..??? [5:8]