Chapter 9 Electricity
Series circuits
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If one component is broken none will work.
Total current decrease after each component (resistor).
Parallel circuits
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If one component is broken the other branches will work
Current splits equal between branches if components are the same
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Ammeter is used to show how current is divided
Advantages of parallel circuits
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Think of examples!!!
Questions 1-5 page 304 – 305
Current and voltage in parallel circuits
What is voltage?
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Its linked to the electrical energy in a circuit
Symbol for volt is V
It is supplied by a cell, battery or power supply
Most cells supply 1.5V
Battery is 2 or more cells
Most batteries supply 6V, 9V or 12V
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Electrical supply come from power stations/generators
o Most countries is 220V to 240V
o Some countries is 110V to 120V
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In a circuit we call the energy source the energy supply
Battery made from 2 cells -
Battery made from many cells -
A 240V main supply -
Measuring voltage
Voltage in series circuit
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Energy is always conserved
Energy change by the component must be equal to the energy of the cell.
Voltage must add up to meet the voltage of cell
Current in series is the same all over, but voltage can change
Adding more components in a series circuit
Voltage:
Ampere:
Voltage in a parallel circuit
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Voltage over each branch is equal to the voltage of the cell
Adding more components in a parallel circuit
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The more branches with components the higher the current through the cell.
Adding more components in a branch will decrease that branch current flow
Voltage for each branch will stay the same as the cell
Questions 1-6 page 313 – 315
Resistance
Resistance – How easy or difficult it is for electrons to move through a material
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Copper wire has a very low resistance (0.5 – 1.0Ω per 100m)
Insulators like plastic has a very high resistance
Resistance is measured in ohms (𝛺)
Some conductors have a high resistance like a Filament of a bulb
o Moving current transfer thermal energy in the filament – cause the light
Increase in resistance → decrease in current
Ohm’s law
Voltage (V) = current (I) x resistance (R)
Volts (V)
= Amps (A) x Ohms (Ω)
Resistors
Questions 1-4 page 322
Practical circuits
Variable resistors
Everyday circuits
Fridge =
Buzzer for warning =
Open door of car
when lights is on =
Questions 1-4 page 328 – 329
Check your progress