Electricity Flashcards
Potential difference / voltage
The energy transferred per coulomb of charge
Voltmeter
Voltage is measured in volts (V) using a voltmeter
A voltmeter must be connected in parallel of the component as it measures the p.d across the circuit
Voltage in a series circuit
The p.d splits along components
Total V = V1 + V2
Voltage in a parallel circuit
The p.d supplied is equal to the voltages across each of the components
V1 = V2 = V3
Current
The amount of charge that passes a specific point in the circuit
Ammeter
Current is measured in amperes (A) using an ammeter
An ammeter must be connected in series with the circuit to measure the current flowing through it
Current in a series circuit
The current remains the same throughout the circuit
Current in a parallel circuit
The current divides at the point where the circuit branches
Resistance
Is the opposition to the flow of charge
Measured in ohms (Ω)
Resistance in a series circuit
When two or more resistors are connected, the combined resistance is higher than the individual resistance
Total R = R1 + R2
Resistance in a parallel circuit
When two or more resistors are connected, the current splits at the branches and does not go through each resistor, therefore the total combined resistance is less than any of the individual resistors
1 / total resistance = 1 / R1 + 1 / R2
Diode
Allows current to flow in a forward direction
The diode has a very high resistance in the reverse direction (current and voltage is never negative)
Light-dependent resistor (LDR)
The resistance of an LDR decreases as light intensity increases
Filament lamp
The resistance of a filament lamp increases as the temperature increases
Resistor
Resistance remains constant as the current changes
Current and voltage are directly proportional
Thermistor
The resistance of a thermistor decreases as the temperature increases
Energy transferred formula
Voltage x charge
Q x V
Energy transferred formula (2)
Power x time
P x T
Charge formula
Current x time
I x T
Power formula
Current x voltage
I x V
Power formula (2)
Current² x resistance
I² x R
Factors that affect resistance practical
Create a parallel circuit
Connect the crocodile clips to the resistance wire, 100 centimetres apart
Record the reading on the ammeter and on the
voltmeter
Move one of the crocodile clips closer until they are 90 cm apart
Record the new readings on the ammeter and the voltmeter
Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm
Characteristics of a variety of circuit elements practical
Create a circuit with a voltmeter around a component (resistor, bulb and a diode)
Ensure that the power supply is set to zero at the start
Record the reading on the voltmeter and ammeter
Use the variable resistor to alter the potential
difference
Repeat steps three to four, each time increasing the potential difference slightly
Repeat the experiment but replace the components
Mains electricity
Is an ac supply
Frequency of 50 Hz and voltage of 230V
Plug
Live wire - brown
Neutral wire - blue
Earth wire - green
Neutral wire
Blue colour
On the left of the plug
0V
Live wire
Brown colour
On the right of the plug
230V
Earth wire
Yellow and green colour
In the middle of the plug
0V
Outer insulation
Made from plastic
Cable grip
This holds the cable tightly in place so that wires do not become loose
Fuse
The fuse melts if the current is too high, breaking the circuit and the flow of current, preventing electrocution
Earthing
When there is a fault the earth wire takes the current from the live wire and sends it to the ground instead of the person touching it
The National Grid
The National Grid distributes electricity across the country
Step-up transformers
Increases the voltage and reduces the current, which reduces energy lost through heat
Step-down transformers
Reduces the voltage from the transmission voltage to the safer voltage of 230 V for home use
Static electricity
When an object becomes charged from friction between insulators
Electric fields
A charged object creates an electric field around itself