Problem solving tips
3 min read

Alternating Current

- Want to score better marks in exams? Have a look at some problem solving tips.
1
Tip 1: Problem based on the calculation of impedances.
  • The calculation of impedance in several circuits is asked in a very tricked manner. Students need to be very careful about the behavior of the circuits at various instants.
  • When asked about the impedance of LCR circuit at resonant frequency, we need not to solve for all components. It is simply the magnitude of resistance in the circuit.
2
Tip 2: Problem based on calculation of voltage across any component.
  • If in the problem there is an EMF source connected across one component and you are asked about the impedance or value of another component that can be safely added to the circuit, first of all make sure that all parameter through the component are the RMS values.
  • If the new component is required to be connected in series, remans the same through both and if it connected in parallel, remains the same.
  • Depending on the nature of component, the net impedance of the circuit can be obtained and thus the value for that component can be found.
3
Tip 3: Drawing the phasor diagram for a circuit.
  • Phasor diagrams play a very important role in determining the phase difference between voltage and current. In order to draw a phasor, first we need to decide a reference.
  • Generally for a parallel circuit, we consider the source voltage as reference whereas in series circuit, we take source current as reference.
  • The drawing of whole phasor should start with the reference first and then drawing all other parameters. However one should keep a note that phasors being vectors can only be added by vector methods of addition.
  • Now we need to remember the phases difference for the three passive components.
  1. Resistor: Voltage and current are in same phase.
  2. Inductor: Voltage leads current by 90 degree.
  3. Capacitor: Current leads voltage by 90 degree.
expand