Electric current flows from the negative end to to the the positive end of the cell (electrons are negative)
Electrons carry energy from the cell and pass it to the components in the circuit such as the lamp (electrical energy is transferred to light and thermal energy)
When electrons return to the positive side of the cell, they are carrying less energy
A) cell
B) lamp
C) open switch
D) closed switch
Series current: has no branches, the current can only flow in one path
Current = flow of electric charge unit- is ampere (A)/amp
Measure current by using an ammeter
Current is never used up in a series circuit, it is the same all the way around
Conventional current: drawing in the opposite direction
Parallel circuits contain branches: some current passes through both of the branches
The current in the branches adds up to the total current leaving the cell
Potential difference (voltage)
Potential difference of 1 volt tells us that 1 joule of energy is transferred for each coulomb of charge that is moving through the circuit
The total p.d across both lamps (in series circuit) is the same as the p.d across the whole cell- the higher the p.d the brighter the lamp will be as it’s transferring more energy
if there are two lamps then the p.d will be /2 because it's being shared
For components connected in parallel, the potential difference
across each component (branch) is the same
Batteries: two or more cells together
Must be connected in the same direction
The volt would multiple by the amount of ‘cells’ present
eg; 3 cells, volt is 9 → 3 x 9 = 18 volts
Electrical charge is measured in coulombs (C)
Current of 1 ampere = 1 coulomb of charge flowing
the size of electric current is the rate of flow of electrical charge
Charge flow (coulombs) = current (amperes) x time (seconds)
Q = I X T
A) charge flow
B) current
C) time
energy transferred (J) = charge flow (c) x potential difference (v)
E = Q x V
As electrons move through a conductor, they collide with atoms in the metal, electrical energy is transferred into other forms (eg: thermal)
Cell contains chemical energy → transferred to electrical energy → carried by current around circuit
Resistance : the potential difference required to drive a current through a component (ohms/Ω) high p.d, high resistance
resistance = p.d / current
R = V/I
Resistors: circuit components that provide a given resistance to a circuit
current through resistor is directly proportional to the p.d
resistance is constant; an ohmic conductor
(will only stay constant if the temperature is constant! )
Filament Lamp: very fine wire (filament) the tightly coiled wire gets hot when a current passes through- this gives off the light
Current through a filament lamp is not directional proportional to to p.d
That's because the filament gets hot, which causes the resistance to increase- at high temp the atoms vibrate more, the electrons in the current collide more with the atoms so more energy is needed to push current through
As p.d increases the current no longer increases as much
Current in diode flows in one direction: it has very high resistance in the reverse direction
Extremely useful for controlling the flow of current in circuits
Light-emitting diode (LED)
Gives off light when current flows through
Extremes energy-efficient source of light
Signs
A) LED
B) diode
Resistors in series add together; the current has to pass through each resistor in turn. It cannot bypass any resistor
Equivalent resistance: you can instead replace multiple resistors with one (eg: 150 resistor instead of 100 and 50)
Current = potential difference / resistance
I = V/R
LDR = Light dependant resistor
In dark conditions the LDR has high resistance, but in light it is low
In light = resistance is low, it takes little energy for current to pass through LDR, the p.d is low
P.d is shared between components so the p.d across the lamp is large and the lamp would let light out
If the phone is help to a person ear, the LDR is in darkness, so the resistance rises sharply; great deal of energy for current to pass through, so p.d across LDR is very high
Less electrical energy for the lamp- p.d is now very low and lamp is dim, screen turns off
Thermistors: resistance decreases when temperature increases
Under cool conditions; the resistance of the thermistor is high which means it takes a lot of energy for the current to pass through - p.d would be high
If temperature is hot, resistance of thermistor falls, less energy for current to pass through thermistor p.d is now low
Required Practical: Resistance
Attach a wire to a metre ruler and then connect the wire to the rest of circuit using crocodile clips- only the part of the wire between the clips is connected - move clips to change the length
Problems:
Zero error- subtract the zero error from the reading (due to crocodile clips not being on zero on ruler, resistance caused between contact of clips and wire)
Heating effect: temperature of wire will increase then resistance will also increase- use a low p.d to keep current low, reducing any heating in the wire & only turn on current when taking a reading
Required Practical : Current / PD Characteristics
Resistor
Read voltmeter to find the p.d across the resistor, use ammeter to read current through the resistor
Then record the values in a table
Adjust the variable resistor and record the new reading on the ammeter & voltmeter (do this multiple times to get a rage of readings)
Switch the direction of the battery, this means the direction of the p.d should reverse- readings should be negative values
Record a range of readings
Required Practical : Current / PD Characteristics
Filament Lamp
Read voltmeter to find the p.d across the filament lamp, use ammeter to read current
Then record the values in a table
Adjust the variable resistor and record the new reading on the ammeter & voltmeter (do this multiple times to get a rage of readings)
Switch the direction of the battery, this means the direction of the p.d should reverse- readings should be negative values
Record a range of readings
Required Practical : Current / PD Characteristics
Diode: Extra resistor: diode are easily damaged by high current- keep current relatively low, because current is slow we need a sensitive ammeter (milliammeter
Read voltmeter to find the p.d across the diode, milliammeter to read current
Then record the values in a table
Adjust the variable resistor and record the new reading on the ammeter & voltmeter (do multiple times to get a range of readings)
Switch direction of the battery - direction of the p.d should reverse- readings should be negative values
Record a range of readings
Energy Transfer by Appliances
Blender and fan = Electrical energy → kinetic energy of electrical motors
Iron & Kettle = Electrical energy → thermal energy
Hair Dryer & washing machine = electrical energy → kinetic energy of motors + thermal energy
Power = the rate at which energy is transferred 1 watt = 1 J per second
Thermal energy appliance needs higher power
energy = power x time
E = p x t
power = p.d x current
power = current^2 x resistance
Current from cell = direct current (electrons only flow in one reaction) Mains power supply = alternating current (constantly changing in direction)
Benefit- easy to use, transformer to increase or decrease the p.d
In UK, Frequency = 50 Hertz (hz), p.d = 230 volts Oscilloscope: to look at AC and DC, Frequency = Number of cycles in one cycle
Main Electricity
The wires are made of copped which is a good conductor of electricity: coating are made of plastic which does not conduct electricity
Brown Wire: live wire carries alternating p.d from power supply (230V)
Connected to a fuse in the plug
Dangerous, fatal if touched: has a high p.d - Current would flow through the person into the earth they'd be electrocuted
Blue wire: neutral, completes the circuit- p.d = 0V compared to the live wire
transfers electricity away from the appliance to avoid overloading
Green & yellow wire: earth wire, a safety wire
Connected into the ground with a metal rod
If the case becomes live, a huge current flows to the earth- the fuse melts and shuts of the current, prevents anyone from getting an eclectic shock from touching the case
Metal cases: can be dangerous
If live wire comes loose and touches metal case, the case can become live: could give someone a fatal electric shock if they touch it.
Acts as a safety wire to stop the appliance from becoming live
National grid: system of transformers and cables
Electricity passed through step-up transformer which increase the potential difference to several hundred thousand volts- less energy is lost in power cables when p.d is high