Resistance-1 = (voltage-1) / (current-1) =
(12 V) / (0.185 A) = 64.9 ohms .
Resistance-2 = (voltage-2) / (current-2) =
(90 V ) / (1.25 A) = 72 ohms .
The resistance changed between situation-1 and situation-2 .
How did that happen ?
Power = (voltage) x (current)
Power-1 = (12) x (0.185) = 2.22 watts
Power-2 = (90) x (1.25) = 112.5 watts
The poor resistor dissipated 51 times as much power during
the second trial. It got all heated up, and its resistance went
through the roof.
Carbon resistors behave nicely and reliably, until you try to
toast bread or light up your bedroom with them.
