Electricity Flashcards
Current (I) definition
A measure of the flow of electrons around the circuit.
Measured in amperes, amps (A) = coulombs per second
Coulomb definition
Amount of electricity that 1 amps of current carries in one second.
Potential Difference (V) definition
Measured in volts (voltage)
Force driving the flow of electrons - measure of how much energy is transferred between two points in a circuit.
P.d. across a power supply or battery is the energy transferred to each coulomb of charge that passes through it.
Resistance (R) definition
Everything that resists or opposes the flow of electrons. Measured in ohms.
Which way does current flow?
Whereas conventional current assumes that current always flows from the positive to the negative.
OHM’s LAW:
V =
voltage =
I x R
current x resistance
OHM’S LAW: when resistance does not change, as we increase voltage, current should increase…
proportionally.
All circuits are a closed loop that include:
- a power source e.g. cell
- something for electrons to flow through e.g. wire
Components: Electrical power
cell; battery
Components: controls the flow of electricity
switch
Components: Filament Lamp
Small bulb - was banned as it’s temperature rises to dangerous temperatures/ inefficient as heat energy is wasted.
Contains metal filament that dramatically increases to high temperatures so much so that it glows, producing light.
Components: Fuses
break is too much current flows through, breaking the circuit - thus protects wires and other components from getting damaged if a faulty appliance has caused too much flow of current.
Components: Diode
only allows current to flow in one direction.
Component: LED
light-emmitting diode
light emmitted when current flows through in the forward direction - light is useful energy and no thermal energy is wasted - efficient
Components: to measure
Ammeter - current/ connected in series with component
Voltmeter - voltage/ connected in parallel
Components: Resistors: LDR
light-dependent resistor - resistance depends on the intensity of light
Components: Resistors: Fixed resistor
fixed to supply a certain number of ohms worth of resistance ALWAYS
Components: Resistors: Variable resistor
can be manually modified to desired amount of resistance
Components: Resistors: Thermistor
resistance depends on temperature
IV graphs fixed answers:
straight line through the normal when “assuming temperature stays constant” and the circuit is made with only wires and fixed resistors
voltage and current increase proportionally thus ohm’s law is obeyed.
IV graphs fixed answers: filament lamp - line through the normal - s shape
The more it heats up, the greater the resistance, so the curve gets less steep as resistance increases - less current can flow per unit of p.d. at high temperatures.
IV graphs fixed answers: Diode - curve when p.d is positive
only allows current to flow in one direction which is why they only show a current when the p.d is positive.
Why does an increase in temperature increase the resistance of wires and fixed resistors?
As temperature increases, the metal ions of the wire vibrate faster which makes it harder for electrons to pass along the wire (resistance increases).
Charge (Q) =
current x time
I x t
1 amp =
1 coulomb/sec
Charge meaning
a measure of the total current that flowed within a certain period of time
In a series circuit, the _____ current passes through each component
same
total current = same everywhere in the circuit
In a series circuit, the total potential difference of the power supply is ________ between the components
shared
total voltage = v1 + v2 + v3 + vn
In a series circuit, total resistance =
sum of all individual resistances of each component
How to calculate the voltage across a single component in series (using equation)
V = IR
we know the I is the same across the whole circuit
the resistance for that single component
times them together
How to calculate the voltage across a single component in series (using voltmeter)
connect in parallel
Due to ohm’s law, components with a greater resistance…
will always have a higher share of the voltage.
Potential difference in parallel circuits
V1 = V2 = V3 = Vt
t is total
Current in parallel circuits
It = I1 + I2 + I3 + In
in parallel circuits, loops that have greater resistance take a _______ share of the current
smaller
Resistance in parallel circuits
1/Rt = 1/R1 + 1/R2 + 1/Rn
the more components or loops there are in the circuit, the lower the resistance
a cell or battery provides a direct current - the current only flows….
in 1 direction and always has the same p.d.
mains electricity provides an alternating current ac - the current repeatedly changes…
direction and has an alternating p.d.
the frequency of mains electricity supply in the UK is ________ and its voltage is ________
50hZ
230 V
The Earth wire =
yellow
stops the appliance becoming live
p.d. of the Earth wire is 0 V - it only carries current if there is a fault
The neutral wire =
blue - completes the wire 0 V
Plastic is used for the wire coatings because it is a…
good insulator
The live wire =
brown
Dangerous because it has a high potential difference of 230 V
Copper is used for the wires because…
it is a good conductor and bends easily
transformers are…
devices that can change the potential difference of an alternating current
the national grid is a nationwide network of cables and transformers that…
link power stations to homes, offices, and other consumers of mains electricity.
short circuit =
when there is a fuse in place -> if the current is too high the fuse will melt and break the circuit
step-down transformer =
decreases the potential difference from the transmission cables to the mains supply in homes and offices so that it is safe to use.
step-up transformer =
used to increase the p.d. from the power stations to the transmission cables
What are the three wires in a cable:
- neutral
- live
- earth
what colour is the live wire and what does it do?
brown - it carried current to the appliance
what colour is the neutral wire and what does it do?
blue - completes the circuit by carrying the current back to the power supply.
what colour is the earth wire and what does it do?
yellow and green - acts as a safety precaution - if the live wire touches the casing of the appliance posing a threat to someone handling the appliance, it provides an alternative route for the electricity to flow.
