A rectangular block of copper has sides of length 15 cm, 26 cm, and 43 cm. If the block is connected to a 5.0 V source across two of its opposite faces, find the following. (a) What is the maximum current the block can carry?

the case is the one  with the greatest current, L=15 cm ,   i = 2.19 10⁸  A

Explanation:

Ohm's law is

          V = i R

Resistance is

         R = ρ L / A

Where L is the length of the electrons pass and A the area perpendicular to the current

      i = V / R

      i = V (A / ρ L)

      i = V / ρ  (A / L)

We can calculate the relationship between the area and the length to know in which direction the maximum currents

Case 1

      L = 0.15 m

      A = 0.26 0.43 = 0.1118 m2

      A / L = 0.1118 / 0.15

      A / L = 0.7453 m

Case 2

        L = 0.26 m

        A = 0.15 0.43 = 0.0645 m2

        A / L = 0.248 m

Case 3

       L = 0.43 m

       A = 0.15 0.26 = 0.039 m2

        A / L = 0.0907 m

We can see that the case is the one  with the greatest current, L=15 cm

Let's calculate the current

     i = 5 / 1.7 10⁻⁸ (0.7453)

      i = 2.19 10⁸  A

more than, less

less than, more