Resistance!

Question

1. Find the resistance of a 30 meter length of copper wire of 0.8 mm diameter.
2. How hot would a copper wire need to be for its resistance to be 3% larger than its value at room temperature (20ºC)?

Answer 1

R = (ρL)/A

 

Where

R = resistance

ρ = resistivity of material (will have to look up for copper)

A = cross sectional area

L = length of wire

Remember to use base units (i.e. meter).

 

To find the new resistance after a temperature change you use the formula: R = R_0(1+α(T-T_0))

R = new resistance

R_0 = resistance at room temperature

α = temperature coefficient (will have to look up for copper)

T = new temperature

T_0 = room temperature

 

You want the resistance to be 3 percent higher so you want R = 1.03*R_0.