# Series and Parallel Circuits

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Series and Parallel Circuits
Chapter 23 Series and Parallel Circuits

Types of Circuit There are two types of electrical circuits;
PARALLEL CIRCUITS SERIES CIRCUITS

SERIES CIRCUITS The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

PARALLEL CIRCUITS The components are connected side by side.
The current has a choice of routes. If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.

Measuring Current Electric current is measured in amps (A) using an ammeter connected in series in the circuit. A

Measuring Current A A This is how we draw an ammeter in a circuit.
PARALLEL CIRCUIT SERIES CIRCUIT

Measuring Current SERIES CIRCUIT
current is the same at all points in the circuit. 2A PARALLEL CIRCUIT 2A 2A current is shared between the components 1A 1A

Measuring Voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter V

Measuring Voltage Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current. Unlike an ammeter a voltmeter is connected across the components Scientist usually use the term Potential Difference (pd) when they talk about voltage.

Measuring Voltage V V This is how we draw a voltmeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT

Series Circuit Voltage is shared between the components 3V 1.5V 1.5V

Parallel Circuit Voltage is the same in all parts of the circuit. 3V

Resistors in Series When two or more resistors are connected end-to-end, they are said to be in series The current is the same in all resistors because any charge that flows through one resistor flows through the other The sum of the potential differences across the resistors is equal to the total potential difference across the combination

Resistors in Series, cont
Potentials add ΔV = IR1 + IR2 = I (R1+R2) Consequence of Conservation of Energy The equivalent resistance has the effect on the circuit as the original combination of resistors

Equivalent Resistance – Series
Req = R1 + R2 + R3 + … The equivalent resistance of a series combination of resistors is the algebraic sum of the individual resistances and is always greater than any of the individual resistors

Equivalent Resistance – Series: An Example
Four resistors are replaced with their equivalent resistance

Resistors in Parallel The potential difference across each resistor is the same because each is connected directly across the battery terminals The current, I, that enters a point must be equal to the total current leaving that point I = I1 + I2 The currents are generally not the same Consequence of Conservation of Charge

Equivalent Resistance – Parallel, Example
Equivalent resistance replaces the two original resistances Household circuits are wired so the electrical devices are connected in parallel Circuit breakers may be used in series with other circuit elements for safety purposes

Equivalent Resistance – Parallel
The inverse of the equivalent resistance of two or more resistors connected in parallel is the algebraic sum of the inverses of the individual resistance The equivalent is always less than the smallest resistor in the group

Equivalent Resistance – Complex Circuit

Ground Wire Electrical equipment manufacturers use electrical cords that have a third wire, called a case ground Prevents shocks

Ground Fault Interrupts (GFI)
Special power outlets Used in hazardous areas Designed to protect people from electrical shock Senses currents (of about 5 mA or greater) leaking to ground Shuts off the current when above this level