Solve the all parts of given problem:
Problem: A cylindrical resistor of radius 3.1 mm and length 1.3 cm is made of material that has a resistivity of 5.9 x 10-5 Ω•m.
Part A: What is the magnitude of the current density?
Part B: What is the potential difference (in V) when the energy dissipation rate in the resistor is 1.3 W?
Please help for the above problem, totally confused!! Show each steps if possible, Thanks.