Calculate the resistance of one metre of copper wire that has a cross–sectional area of about 2 x 10-2 cm2 (using the value of resistivity of copper to be 1.2 × 10-8 ohm m) Compare the value of this resistance with that of a flashlight bulb, which has a power rating of 1 W and operates at 3 V. What does this comparison tell you ?
Length of the wire l = 1 m
Area of cross section of the wire A = 2 × 10-2 cm2
= 2 × 10-6 m2
Resistivity of copper ρ = 1.2 × 10-8 ohm m
Therefore R =
= 
= 0.6 × 10-2 Ω The resistance of a flash bulb of power rating 1W and voltage 3V has a resistance R′ = 
= 9 ΩThis clearly shows that the resistance of a flashbulb is much greater than the resistance of the copper wire of 1m length.
Area of cross section of the wire A = 2 × 10-2 cm2
= 2 × 10-6 m2
Resistivity of copper ρ = 1.2 × 10-8 ohm m
Therefore R =
= = 0.6 × 10-2 Ω The resistance of a flash bulb of power rating 1W and voltage 3V has a resistance R′ = = 9 ΩThis clearly shows that the resistance of a flashbulb is much greater than the resistance of the copper wire of 1m length. AI is thinking…
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