Q35 of 72 Page 12

A copper wire has a diameter of 0.5 mm and resistivity of 1.6 ohm cm. How much of this wire would be required to make a 10 ohm coil?

Diameter of copper wire, D = 0.5mm Therefore Area of cross section A = = 0.1963 mm2 Resistivity of the copper wire ρ = 1.6 ohm cm = 16 ohm mm Let the required length be l Then l = R ×
        =10 ×
        = 0.12269 mm
        = 122. 7 × 10-6 m

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33 A piece of wire having resistance, R is cut into four equal parts. 
(i)  How will the resistance of each part compare with the original resistance?
(ii) If the four parts are placed in parallel, how will the resistance of the combination compare with the resistance of the original wire? 34 A piece of wire is redrawn by pulling it until its length is doubled. Compare the new resistance with the original value? 36 Draw a schematic diagram of a circuit consisting of a battery of four 2 V cells, a 5 ohm resistor,  an 8 ohm resistor and a 12 ohm resistor and a plug key all connected in series. 37 Redraw the circuit of problem 6, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the voltage across the 12 ohm resistor. What would be the readings in the ammeter and the voltmeter.