Hard calculas question?
A voltage V across a resistance R generates a current C = V/R. Suppose a constant voltage of 12 volts is put across a resistance that is decreasing at a rate of 0.4 ohms per second when the resistance is 4 ohms.
(a) At what rate is the current changing?
dC/dt
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Verified answer
c = v / r
dc/dr = -v/r²
dc/dt = (dc/dr) (dr/dt) .................. chain rule
dc/dt = (-12/(4)²) (-0.4) ............... dr/dt given as -0.4 ohms/s
dc/dt = 3/10 amp/s
Answer: 3/10 amp/s