Power and Electrical Energy
Power and Electrical Energy
- Work (W) is a function of force (F) and displacement (s) - \(W=Fs\) OR E = energy and \(E=Fs\)
- \(P = \frac{E}{t}\)
- \(P = IV\)
- But also \(V=IR\)
- So \(P=IIR\)
- Or \(P=I^2R\)
Calculating current in a circuit
Diagram: 12V - 120 ohms in series with a 80 ohm and 40 ohm in parallel
- \(\left( \frac{1}{40}+\frac{1}{80} \right)^{-1}=\frac{440}{3}\)
- \(\frac{12}{\frac{440}{3}}=\frac{9}{110}\)
- Current across 40 ohm resistor = \(\frac{3}{110}=0.0\dot{2}\dot{7}\)
- Current across 80 ohm resistor = \(\frac{3}{55}= 0.0\dot{5}\dot{4}\)
- Current across the 80 ohm branch only = \(0.054\times120=\frac{72}{11}\)
- \(12-\frac{72}{11}=5.\dot{4}\dot{5}\) or \(\frac{60}{11}\)
Another practise question
- 38 ohms across the circuit
-
current = \(\frac{6}{38}\)