The wires of our appliances are insulated with a material mixed with rubber, which has a very high resistivity. If a certain wire has a length of 2.5 m and the outer diameter is 5mm and its inner diameter is 0.5mm, what is its resistance? Note that the inner diameter is present to leave a hallow place where conducting wire ( usually copper) is present. Follow the format: Given: Required: Equation: Solution: Answer:

1- Some copper wire has a resistance of 200 at 20°C. A current is passed through the wire and the temperature rises to 90°C. Determine the resistance of the wire at 90°C, correct to the nearest ohm, assuming that the temperature coefficient of resistance is 0.004/°C at 0°C

An aluminium rod with square cross section is 1.3 m long and 3.8 mm on edge ) What is the resistance between its ends? The resistivity of aluminium is 2.75 - 10-8 Q.m. (ii) What must be the diameter of a cylindrical copper rod of length 1.3 m if its resistance is to be the same as that of the aluminium rod? The resistivity of copper is 1.69 * 10-8 Q.m. (iii) Calculate the current (in A) and the current density (in A/m^2) of the cylindrical copper if the potential drop across the ends of the wire is 0.060 V. Select one: a. (i) 3.27 x 10-30 (ii) 15.3 × 10-3 m (iii) l= 18.3 A and J=1 x 105 A/m2 b. (i) 2.50 x 10-3n (i) 3.4 × 10-3 m (iii) l= 24 A and J=2.64 x 10 A/m2 c. (i) 2.50 x 10-3 (ii) 3.4 x 10-3 m (iii) l= 24 A and J=2.08 x 106 A/m2 d. (i) 3.27 x 10-3 (ii) 8.14 x 10-3 m (iii) l= 18.3 A and J=2.64 x 106 A/m2

A copper wire has a resistance of 0.85 ohm at 200C. What will be its resistance at 400C ? Temperature coefficient of resistance of copper at 00C is 0.004/0C.

Notes on the verification of ohm's law by voltage method?

Only 2