Question

The energy transfer to a device is 112 000 J when there is a potential difference of 185 volts across it. If the current through the device is 0.0644 A, how long in hours is the current flowing? 

Answer 1

The power supplied by the device is given by

$P=V I$

Where.

$V=185\;V$ Is the voltage.

$I=0.0644 A$ Is the current.

Evaluating numerically.

$P=V I\\ P=185\;V\times 0.0644\;A\\ P=11.9\;W$

But remember that the power is given by

$P=\dfrac{E}{t}$

Where.

$E=112 000\;J$ Is the energy.

$t$ Is the time.

Obtaining the expression for time

$P=\dfrac{E}{t}\\ P\;t=E\\ t=\dfrac{E}{P}\\$

Evaluating numerically in seconds.

$t=\dfrac{E}{P}\\ t=\dfrac{112 000 J }{11.9\;W}\\ t=9411.8\;s$

The time in which the current flows is.

$t=9411.8\;s$