Series and Parallel Circuits · Parallel, Example Equivalent resistance replaces the two original...
Transcript of Series and Parallel Circuits · Parallel, Example Equivalent resistance replaces the two original...
Series and Parallel Circuits
Types of Circuit
There are two types of electrical circuits;
SERIES CIRCUITSPARALLEL CIRCUITS
The components are connected end-to-end, one after the other.
They make a simple loop for the current to flow round.
SERIES CIRCUITS
If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.
PARALLEL CIRCUITS
The current has a choice of routes.
The components are connected side by side.
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
AA
This is how we draw an ammeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
Measuring Current
SERIES CIRCUIT
PARALLEL CIRCUIT
• current is the same at all points in the circuit.
2A 2A
2A
• current is shared
between the
components
2A2A
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
Different cells produce different voltages. The
bigger the voltage supplied by the cell, the bigger
the current.
Measuring Voltage
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
This is how we draw a voltmeter in a circuit.
SERIES CIRCUIT PARALLEL CIRCUIT
V
Series Circuit
1.5V
• Voltage is shared between the components
1.5V
3V
• Voltage is the same in all parts of the circuit.
3V
Parallel Circuit
3V
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
Equivalent Resistance
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
321eq R
1
R
1
R
1
R
1
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
Equivalent Resistance Series Circuits
Req = R1 + R2 + R3 + …
Equivalent Resistance Parallel Circuits
321eq R
1
R
1
R
1
R
1