Transcript P5 Electric Circuits

Grade Boundaries
A* 90%
A 80%
B 70%
C 60%
P5
Electric
Circuits
Model of the Atom
• Electrons
Negative
• Protons
Positive
• Neurons no
charge
Static Electricity
• Materials can only
lose or gain Electrons
• Protons don’t move
• This will make them
positive or negative
• Static Electricity only
happens between
two insulators.
• Conductors direct the
charges to the Earth.
Structure of Metals
• Conductors
– Electrons free to
move
• Insulators
– Electrons are
not free to move
Circuit Symbols
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•
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Open Switch
Closed Switch
Lamp
Cell
Battery
Voltmeter
Resistor
Ammeter
Variable resistor
Thermistor
Light dependent resistor
(LDR)
Resistance
• Moving electrons can collide with atoms of a
conductor. This is called resistance.
• Resistance makes it harder for the current to flow.
• These collisions also make a conductor hot. EG: this
is why a light bulb is hot.
Thermistors
• Low Temperatures = High Resistance
• High Temperatures = Low Resistance
Light Dependent
Resistors
• Darkness = High Resistance
• Light = Low Resistance
Complete / Incomplete Circuits
• Ammeter
– Measures Current in
Amps.
– Must be connected
in series.
• Voltmeter
– Measures Voltage
(Potential Difference)
in Volts
– Must be connect in
parallel
Series / Parallel Circuits
• Series: if lamp
breaks, circuit
breaks
• Parallel: if
lamp breaks,
the other lamp
will still work
Series Circuits
–Atotal = A1=A2=A3
–Vtotal = V1+V2+V3
Parallel Circuits
–Atotal=A1+A2+A3
–Vtotal=V1=V2=V3
Ohm’s Law
• The current is directly
proportional to the
voltage.
• IE: if you double the
voltage, the current will
also double.
Resistors in Series and Parallel
Electromagnetic Induction
•
Moving a magnet
through a coil of wire
produces an electric
current.
•
To increase the voltage
you can:
1. Move the magnet faster
2. Use a stronger magnet
3. Increase the number of
coils
Electric Generator
•
•
•
Rotating coil inside a magnet
The size of the induced voltage can be increased by:
1. Increasing the speed of rotation of the coil
2. Increasing the strength of the magnetic field
3. Increasing the number of turns on the coil
4. Placing an iron core inside the coil
Generators produce Alternating Current
AC/DC
• Alternating Current: Produced in
Generators. Current reverses it’s flow every
half turn of the magnet.
• Direct Current: Produced by a battery.
Current flows in only one direction.
Transformers
• Change the Voltage of an AC supply
• Step-Up Transformer: Increases Voltage
• Step-Down Transformer: Decreases Voltage
Transformers
• Primary coil connected to AC supply
• Changing current produces a changing Magnetic Field
• This induces an AC in the secondary coil
Transformer Equation
Secondary Voltage = Number of Coils Secondary
Primary Voltage
Number of Coils Primary
Power
Energy Transferred
Energy Transferred = Power x Time
Energy = kilowatt-hours
Power = kilowatts (1000 watts)
Efficiency
• Energy cannot be created or destroyed. It can
only be transferred from one form to another.
• Most Electrical Energy is wasted in a lightbulb
as Heat Energy.
Cost of Electricity
Cost = Number of Units x Cost of One Unit
Efficiency
Efficiency = (useful energy/total energy)x100