Download circular powerpoint

Electric Circuits
Explaining
Electric
circuits
P5.5 Measuring
resistance
P5.4 Resistors in
parallel
P5.1 Static
electricity
P5.2 Current and
voltage
P5.4 Resistors in
Series
Introduction
Electric Circuits
21st Century P5.1 – 5.5
Electric Circuits
•
•
•
•
•
P5.1 Static Electricity
P5.2 Current and Voltage
P5.4 Resistors in series
P5.4 Resistors in Parallel
P5.5 Measuring resistance
We will be examining the above sections and any
formulas relating to them.
Task
Use the presentation and your own
knowledge to complete the electric circuits
work sheet. You will then use this sheet to
complete some past paper questions.
Electric Circuits
Explaining
Electric
circuits
P5.5 Measuring
resistance
P5.4 Resistors in
parallel
P5.1 Static
electricity
P5.2 Current and
voltage
P5.4 Resistors in
Series
Static Electricity
Some staff felt that shock therapy was going too far to
What is it?
Static charge is literally charge that cannot
move. It is static. The charge in this case is
an electric charge.
The particles that move are electrons. They
have a negative charge.
How to create it
Demonstration of static
electricity
Experimenting with static charge
Uses of static electricity
 photocopiers
and laser
printers
 spray painting cars
 filtering
factory
smoke
 heart
defibrillators
Electric Circuits
Explaining
Electric
circuits
P5.5 Measuring
resistance
P5.4 Resistors in
parallel
P5.1 Static
electricity
P5.2 Current and
voltage
P5.4 Resistors in
Series
Current and Voltage
Definition - Current
• A flow of electric charge – Usually
electrons
Definition - Voltage
 The amount of energy transferred to or from
charges when they pass between two points
Conductors and insulators
• Conductors have large numbers of free
electrons. This makes it easy for current to
flow through them.
• Insulators have very few free electrons. This
makes it hard for current to flow through
them.
Measuring current
• We use a ammeter to measure current. The
unit of current is the amp. An ammeter is
wired in series.
Measuring voltage
• Voltage is measured using a voltmeter. It is
measured in volts (V) a voltmeter is
connected in parallel
Electric Circuits
Explaining
Electric
circuits
P5.5 Measuring
resistance
P5.4 Resistors in
parallel
P5.1 Static
electricity
P5.2 Current and
voltage
P5.4 Resistors in
Series
Resistors in series
Resistance
• All electrical components have resistance.
They convert the energy from the electrons
into other forms of energy, often heat.
• If there are multiple components we need to
be able to add them together. Components
can be connected in series or parallel
Formula
• Components in series follow one after the other
whereas components in parallel run along side by
side.
• We can add resistors in series together with the
following formula :-
RT  R1  R 2  R3  .......
Units
• The unit for resistance is the ohm.

Additional Notes
• If an component has a high resistance it
converts a large amount of electrical energy
as the current flows through it.
• i.e A lamp with a high resistance will
change more electrical energy into light
Electric Circuits
Explaining
Electric
circuits
P5.5 Measuring
resistance
P5.4 Resistors in
parallel
P5.1 Static
electricity
P5.2 Current and
voltage
P5.4 Resistors in
Series
Resistors in parallel
Resistors in parallel
• We also need to be able to add resistors in
parallel.
• Parallel resistors run side by side
• This gives an extra route for the current to
flow through
• Because of this the overall resistance is less
than the resistance of any individual resistor
Formula
 This is the formula for calculating the total
resistance of resistors in parallel
1
1
1
1
 

 ......
RT R1 R2 R3
Additional notes
• The gradient of the line in a current voltage
graph represents the value of the resistance.
The steeper the line the higher the
resistance.
Electric Circuits
Explaining
Electric
circuits
P5.5 Measuring
resistance
P5.4 Resistors in
parallel
P5.1 Static
electricity
P5.2 Current and
voltage
P5.4 Resistors in
Series
Measuring resistance
Measuring resistance
• The size of the current flowing in a circuit
depends on the voltage of the cell and the
resistance of the circuit.
• This means that the size of the resistance
can be found if we know the current and
voltage in a circuit
Formula
• Voltage = Current X Resistance
• V=IR
V = Voltage
I = Current
R = Resistance
Units
• Voltage is measured in volts (v)
• Current is measured in amps (A)
• Resistance is measured in ohms (Ω)
Current voltage graph
• The graph opposite shows
current passing through a
resistor plotted against the
voltage across a resistor. As it
is a straight line it shows if we
double the voltage we will
double the current
Electric Circuits
Explaining
Electric
circuits
P5.5 Measuring
resistance
P5.4 Resistors in
parallel
P5.1 Static
electricity
P5.2 Current and
voltage
P5.4 Resistors in
Series