A high-wattage resistor for employ in a dc power supply is formed through depositing Carbon containing a square cross-section to an insulated former containing a cylindrical shape along with a diameter of 2.5 millimetres. A section with the component is demonstrated in figure below. The length of the resistor that uses Carbon containing a resistivity of 4.5 x 10-5 as its base material is 2.5 cm. Find out the outer dimension 'a' required to generate a resistance of 0.5 ?.
Figure: Cross Section of the Resistor