Electricity Flashcards
Current is measured in
amps
Current is the
rate of flow of positive charge at a point
At a junction, current is
conserved
Current is measure with
an ammeter in series
In a metal, current flows via
electrons
In a liquid, current flows via
ions
Potential Difference is also known as
Voltage
Voltage is
work done per unit charge
Voltage is measured with
a voltmeter in parallel
Resistance is measured in
ohms
Ohmic conductors have
constant resistance
An example of an ohmic conductor is
a resistor
Non-ohmic conductors have
variable resistance
An example of a non-ohmic conductor is
a filament lamp
With a thermistor, resistance
decreases as temperature increases
With a Light Dependent Resistor (LDR), resistance
decreases as light intensity increases
Components in Series are
end to end
In a series circuit, current is
conserved
In a series circuit, voltage is
shared (this is governed by each component’s resistance)
In a series circuit, the total resistance is
the sum of the individual resistances
Components in parallel are
in separate branches
In a parallel circuit current is
shared between brances
In a parallel circuit voltage is
the same across each branch
Parallel circuits are advantageous because
faults are isolated
Three hazards associated with Mains Electricity
- Damaged insulation can lead to shock or fire.
- High currents can heat wires causing insulation to melt leading to shocks or fires.
- Damp conducts electricity leading to shocks
Common fuse sizes
3A, 5A and 13A
A fuse is
a thin wire which overheats and melts when current is too high, thus protecting the circuit
A circuit breaker is
an electromagnetic switch which breaks when the current is too high.
Circuit breakers are better than fuses because
they can be reset and they work more quickly than fuses.
Earthing wires offer
a safe route if there is a short circuit as they have a very low resistance
Double insulation is a
plastic casing covering components
Power (P) equals
Current x Voltage or IV
Energy (E) equals
Charge x Voltage or QV
Charge (Q) equals
Current x Time or IT
Voltage (V) equals
Current x Resistance or IR
Describe what happens and why to resistance as current increases
- Current increases
- Temperature increases
- Electron vibration increases
- Electron collisions increase
- Resistance increases
AC is
Alternating Current which continuously changes direction
DC is
Direct Current which is always in one direction
Opposite charges
Attract
Likes charges
Repel
Charging involves
adding (negative charge) or removing (positive charge) electronsh
Charging creates
ions
Conductors allow
electron flow
Insulators impeded
electron flow
Describe how insulators become charged
When rubbed together, friction causes electrons to move from one (which becomes positively charged) to the other (which becomes negatively charged).
Two examples of Static Electricity
Lightning and charged balloon on a wall
How does lightning come about
- Electrostatic charge builds in clouds due to friction.
- When charge is large enough it is discharged through air to ground as lightning.
Why does a rubbed balloon stick to a wall?
- A rubbed balloon which is positively charged when held near a wall will repel the positive charge in the wall.
- Now negatively charged wall and positively charged balloon will be attracted as they have opposite charges.
Dangers of static electricity
- Electric shock when electrons flow from object through charged body to earth.
- When fuelling aircraft, charge created by friction on equipment could cause a spark and ignition.
Static electricity safety measures
Earthing as it allows electrons an alternative path and so there is no charge build up.
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