# Munali Boys High School/CURRENT ELECTRICITY/CHAPTER 2: ELECTRIC CIRCUITS

## CHAPTER 2: ELECTRIC CIRCUITS

This chapter is meant for pupils of physics in high schools.

# Preknowledge

 Before the chapter, pupils should do the basics of current electricity,namely: current, voltage,potential difference and effective resistance

Objectives
 At the end of this topic pupils should be able to define an electric circuit,distinguish between a series and a parallel circuit,calculate effective resistance,current and potential difference in cicuits

# Assessment

 Pupils should do an exercise at the end of the notes below

Definition
 An electric circuit is a path in which current flows.An example of this may be a single copper wire whose two ends are connected to a battery

## TWO TYPES OF CIRCUIT

There are two types of electric circuits.These are:

1. Series Circuit
2. Parallel Circuit

Definition
 A series circuit is one in which the components come one after the other along the same loop

Definition
 A parallel circuit is one in which the components (resistors) are connected in separate loops

{{Key points|On Series and Parallel circuits:

1. In a series cicuit the formula below is used to calculate the effective resistance.
            R = r1 + r2 + r3....      Where: R = effective resistance and r1,r2 and r3.... are the given
resistance values.


If the resistors are connected in parallel their effective resistance is found from the formula below.

              1/R = 1/r1 + 1/r2 + 1/r3.........

1. The current is the same everywhere in a series circuit. Therefore, same current flows through every component.

In a parallel circuit current is shared by the components(resistors).The higher the resistance of a component, the lower is the current that flows through it.In both cases(series and parallel circuits),current is calculated calculated from the formula: I = V/R Where: I = current, V = voltage and R = effective resistance

1. In series and parallel connections, the potential difference is found from the formula below
              P.d = Ir                 where: P.d = potential difference across a component
I  = current through the component
r  = resistance of a component


In a series circuit the p.d depends on the resistance of a component.The higher the resistance the higher is the p.d across it.In a parallel circuit the p.d across each resistor is the same.Therefore, p.d acros r1=p.d across r2 = p.d across r3 etc.

# Self Assessment

 what is an electric circuit? How does a series circuit differ from a parallel circuit? A current of 4A flows through a component. The p.d across the component is 8V. calculate the resistance of the component