A rectangular block of iron has a cross section of 1.2 cm x 1.2 cm * 15 cm. What is the resistance of the opposing square ends? What is the resistance between two of the rectangular faces?

Answer 1

To answer this, you need to know the resistivity of the material, which is the resistance between two parallel faces of a cubic meter of the material. Let's call it RHO (ohm-meters).

Resistance is RHO x length of the material in meters divided by the cross sectional area in square meters.

Your material's cross section is 1.2cm x 1.2cm, or 1.44 cm squared, and 15 cm long.

Converting everything to meters, you get (RHO x (0.15 meter)) / (1.44 x 10^-4 meters squared) = approx. RHO x (0.1 x 10^4)/meter. A uniform bar of iron at 20 degrees celsius has a resistivity of about 100 nano ohm.meter (100 x 10^-9 ohms,meter).

So finally, the resistance is approx (100 x 10^-9 ohm,meter) x (1 x 10^5)/meter = 1 x 10^-2 ohm.