## 18.  D.C. Circuits

Content

•      Current and potential difference in circuits

•      Series and parallel circuits

•      Potential divider circuit

•      Thermistor and light-dependent resistor

Learning  Outcomes

Candidates should be able to:

(a)   draw circuit diagrams with power sources (cell, battery, d.c. supply or a.c. supply), switches, lamps, resistors (fixed and variable), variable potential divider (potentiometer), fuses, ammeters and voltmeters, bells, light-dependent resistors, thermistors and light-emitting diodes

(b)  state that the current at every point in a series circuit is the same and apply the principle to new situations or to solve related problems

(c)   state that the sum of the potential differences in a series circuit is equal to the potential difference across the whole circuit and apply the principle to new situations or to solve related problems

(d)   state that the current from the source is the sum of the currents in the separate branches of a parallel circuit and apply the principle to new situations or to solve related problems

(e)   state that the potential difference across the separate branches of a parallel circuit is the same and apply the principle to new situations or to solve related problems

(f)    recall  and  apply  the  relevant relationships, including R  =  V/I  and  those  for  current,  potential differences and resistors in series and in parallel circuits, in calculations involving a whole circuit

(g)   describe the action of a variable potential divider (potentiometer)

(h)  describe the action of thermistors and light-dependent resistors and explain their use as input transducers in potential dividers

(i)    solve simple circuit problems involving thermistors and light-dependent resistors