Given: A material with a bulk resistivity of ? = 120 Om is to be used to manufac

Question

Given: A material with a bulk resistivity of ? = 120 Om is to be used to manufacture a 75 kO resistor that must dissipate P = 80 W of power. The maximum allowable current density for this material is J = 120 A/m2. The shape of the resistor is a rectangle.

Required: Determine the resistor length in cm, cross-sectional area in cm2, the maximum allowable applied voltage and the maximum allowable current.


i found the voltage and the current, but no answer i try to input for the length or cross-sectional area works.

Explanation / Answer

we know that ?=120 Om    or 12k Ocm ?12k=RA/l (where R is resistance, A is area, and l is length)
?A/l=12k/75k    =0.16 now max current density=120=I/A and P=I2R=80    ?80=I2*75k I=0.0326A back to current density, 120=0.0326/A A=2.72x10-4 m2 ?in cm2, A=2.72 cm2
back to resistivity: 2.72/l=0.16
l=17cm

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