Exam Lessons Physics

Series RLC Circuits, Resonant Frequency, Inductive Reactance & Capacitive Reactance – AC Circuits


New School physics pag 458-463


  1. Why is water not used as a thermometric substance.
  2. Differentiate between evaporation and boiling.


  1. A voltage supply of 12V r.m.s anf frequency of 90Hz is connected to a 4Ω resistor. Calculate the

peak value of the current . (a) 48.8A  (b) 30.0A (c) 27.5A (d)4.2A

  1. A 2µF capacitor is in series with a resistor of 5000Ω. A voltage of 5V r.m.s  and frequency, I= 100Hzis connected to them. What is the capacitive reactance?
  2. 795.5Ω  (b) 895.5 Ω (c)1795Ω (d) 2005.0Ω

3.   At what frequency will 20uf capacitor have a reactance of 500 ohms?

      (a)   100Hz                   (b)   50Hz         (c)        150Hz  (d) 100π Hz      (e) 30Hz

                  π                                  π                                     π                   π               π

4.   In an RLC series a,c circuit power is dissipated in (a) Resistance only           (b) Reactance only      (c) Resistance and reactance (d) Resistance, inductance and capacitance

5.   In a series L-C circuit, the inductance and the capacitance are 0.5H and 20µF respectively. Calculate the resonance frequency of the circuit (a) 24.2Hz (b) 36.7Hz (c) 50.3Hz (d) 60.5Hz


  1. Explain what is meant by the terms impedance, phase angle and reactance as applied to  an a.c. circuit. Calculate the impedance and phase angle for an a.c. circuit having a 100ohms resistance, 5uf capacitor in series if an a.c voltage of frequency 100Hz is applied across the circuit.
  2. Draw a vector diagram of the relationship of  I and V for an a.c. circuit containing

            (a) a pure inductor                  (b) a pure capacitor                (c ) a pure resistor