Topic 10 - Electricity and circuits Flashcards
Symbols needed for circuits
Cell, battery, open switch, closed switch, filament lamp, fuse, LED, power supply, resistor, variable resistor, ammeter, voltmeter, diode, LDR, thermistor, motor
Series circuits are
Circuits where components are connected from negative to positive in one line(except voltmeters)
If one component of a series circuit disconnects,
The whole thing stops working
Series circuits rules
Bigger supply voltage when there are more cells
The current is the same everywhere
The total voltage is shared between components
The total resistance increases when resistors are added
Parallel circuits are
Circuits where each component is seperately connected to the + and - of the supply(except ammeters)
If one component disconnects in parallel,
It doesnt affect the whole circuit
Parallel circuits rules
Potential difference is the same across all components
Current is shared between brances, so the total current is each parts current added together
There are junctions where the current splits and rejoins with equal magnitude at the end
The total resistance of circuit decreases if another resistor is added in parallel
Voltage/Potential difference is
The force driving the charge round. The energy transferred per coulomb of charge passed
1V =
1J per Coulomb
Energy transferred(J) =
Charge Moved(C) x Potential Difference(V)
Voltmeters measure
Voltage
Voltmeters are always connected in
Parallel
Ammeters measure
Current
Ammeters are always connected in
Series
Current is
The flow of electrical charge around the circuit
Current only flows if
There is a potential difference and the circuit is complete
Charge(C)=
Current(A) x time(s)
When current splits at a junction and rejoins after,
The current is conserved
Resistance is
Anything that flows the current down
The higher the resistance,
The lower the current
Potential difference(V)=
Current(A) x Resistance(Ohms)
How do resistors work
The electrons collide with the ionic lattice , so it is harder to flow through.
Temperature increases due to ions vibrating
This makes it harder for current to flow
Adding resistors in series means……, why?
The total resistance increases.
The voltage is shared between resistors. This reduces voltage and current.
The current is the same everywhere so total current decreases, leadign to resistance increasing
Adding resistors in parallel means…. ,why?
The total resistance decreases.
Adding an extra loop, and the potential difference is the same as the total
This means that the total current increases
To investigate the relationship of V, I, and resistance in series
The standard test circuit is used. Contains an ammeter, main component being tested, and voltmeter
Core practical: Constructing circuits to investigate relationship of V, I, resistance process
Connect standard test circuit
Use fixed resistor or filament lamp as component
Change potential difference of power supply, and measure current and voltage
Plot on graph and calculate resistance
Make sure circuit doesnt get too hot as it changes results
IV Graph for fixed resistors
Linear graph as current and voltage are directly proportional
Filament lamp IV graph
Non-linear
Goes neagtive in current because current can flow both ways if voltage is negative
Diode IV graph
Non linear but doesnt go negative current
Current only flows in one direction
LDR is
A light dependant resistor
LDR resistance pattern
In bright light, resistance increases
Vice versa
Thermistors are
A temperature dependant resistor
Thermistor resistance pattern
In hot conditions, resistance drops
Vice versa
Opposite of normal resistor
How to change circuit to test diode
Switch direction of diode after measurement to observe no current
How to change circuit to test thermistors
Keeping voltage the same, heat thermistor gradually. Resistance decreases
How to change circuit to test LDRs
Conduct experiment in dim room. Use dimmer switch to slowly change light level
When there is an electric current in a resistro,
There is energy transfers to thermal energy stores in the resistor
Electrical energy is dissipated as
Thermal energy in the surroundings
How to reduce unwanted energy transfer in wires
Use low resistance wires
Advantgaes of heating effect in wires`
Used in appliances to heat things. Current passes through and makes resistors hot, which heats things up.
Also used in filament bulbs
Disadvantages of heating effect in wires
Reduces efficiency
Can melt components
Energy transferred(J) =
Current(A) x Voltage(V) x Time(s)
Power is
The energy transferred per second and is measured in Watts
Power(W) =
Energy transferred(J) / Time(s)
Electrical power is also related to
The potential difference and current of the appliance
Electrical Power(W) =
Current(A) x Potential difference(V)
(When V isnt known) Electrical power(W) =
Current(A)^2 x Resistance(Ohms)
Two types of electricity supplies
Ac and DC
AC is
Alternating current, the current is travelling in alternating directions.
UK mains supply is
AC
DC is
Direct current. The current only travels in one direction
Cells and Batteries use
DC
UK mains supply voltage and frequency
230V
50Hz(times current alternates per second)
3 wires in plugs
Live wire - Brown
Neutral wire - Blue
Earth wire - Green and yellow
Live wire is
The wire carrying the voltage
Neutral wire is
Completes the circuit, so current can flow
Has no voltage
Earth wire
For safety and protecting wiring.
Carries current away if something goes wrong
How do fuses work
Connected to live wire so that if there is a surge in current, it melts and breaks the circuit. This means that current doesnt flow through casing and cause elctric shock
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