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Q85PE
Expert-verified(a) How much power is dissipated in a short circuit of \(240 - V\)\({\rm{AC}}\) through a resistance of \(0.250{\rm{ }}\Omega \)?
(b) What current flows?
If a potential difference \(\Delta V\) is maintained across a circuit element, the power or rate at which energy is supplied to the element, as,
\(P = I\Delta V\)
Because the potential difference across a resistor is given by \(\Delta V = IR\), we can express the power delivered to a resistor as,
\(\begin{align}{}P = {I^2}R\\ = \frac{{{{\left( {\Delta V} \right)}^2}}}{R}...(1)\end{align}\)
The energy delivered to a resistor be electrical transmission appears in the form of internal energy in the resistor.
Ohm's Law:
The current \(I\) through a circuit element (other than a battery) can be determined by dividing the potential difference \(\Delta V\) across the circuit element by its resistance \(R\) as,
\(I = \frac{{\Delta V}}{R}...\left( 2 \right)\)
a.
The power dissipated in the circuit is found from Equation \((1)\)as,
\(P = \frac{{{{(\Delta V)}^2}}}{R}\)
Entering the values for \(\Delta V\) and \(R\), it is obtained as,
\(\begin{align}{}P &= \frac{{{{(240\;V)}^2}}}{{0.250{\rm{ }}\Omega }}\\& = 2.30 \times {10^5}\;W\\ &= \left( {2.30 \times {{10}^5}\;W} \right)\left( {\frac{{1\;kW}}{{1000\;W}}} \right)\\ &= 230\;kW\end{align}\)
Therefore, the value for the power is obtained as \(P = 230\;kW\).
b.
The current in the insulator is found by using Ohm's law from Equation \((2)\)as,
\(I = \frac{{\Delta V}}{R}\)
Entering the values for \(\Delta V\) and \(R\), it is obtained as,
\(\begin{align}{}I = \frac{{240{\rm{ }}V}}{{0.250{\rm{ }}\Omega }}\\ = 960{\rm{ }}A\end{align}\)
Therefore, the value of the current is obtained as \(I = 960{\rm{ }}A\).
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