When a resistor is connected to a 12-V source, it draws a 185-mA current. The same resistor connected to a 90-V source draws a 1.25-A current. (a) Is the resistor ohmic? Justify your answer mathematically. (b) What is the rate of Joule heating in this resistor in both cases?

The resistor is not Ohmic

Explanation:

In the first case, from ohm's law: V=IR

R=V/I= 12/0.185=64.9 ohm

In the second case:

R=V/I= 90/1.25= 72ohm

The relationship between voltage and current is linear according to ohms law but that is not the case here.

Joule heating = I^2R

For case1: (0.185)^2 × 64.9 = 2.2W

For case2: (1.25)^2 ×72 =112.5W

the answer is definitely c.

the current is 0.6

voltage ÷ resistance = current

so 12 ÷ 20 = 0.6