Depends on both the resistance (R) of the component and the potential difference (V) across the component
Relationship between resistance and current
The greater the resistance of the component, the smaller the current for a given potential difference across the component
Ohm's Law
V = IR, where V is the potential difference in volts (V), I is the current in amperes (A), and R is the resistance in ohms (Ω)
If the resistance is constant, an ohmic conductor, current is directly proportional to the potential difference
If the resistance of components such as lamps, diodes, thermistors, and LDRs is not constant, the graph is nonlinear
Resistance increases with current as electrons transfer energy to atoms, causing them to vibratemore
Resistance changes with temperature, length, light intensity, and voltage
Total resistance for two resistors in parallel is less than the resistance of the smallest resistor
Total current into a junction
Total current in each of the branches
Potential difference across each "branch"
Is the same
The total resistance for two resistors in parallel is less than the resistance of the smallest resistor
Mains electricity in the United Kingdom has a frequency of 50 Hz and is about 230 V
AC is alternating current, which comes from the mains
DC, direct current, is the movement of charge in one direction only
Wires in a plug
Live wire
Neutral wire
Earth wire
Live wire
Brown, at 230V
Carries the alternating potential difference from the supply
May be dangerous even if mains circuit is off, as current may still be flowing through it
Neutral wire
Blue, at 0V
Completes the circuit
Earth wire
Green and Yellow stripes, at 0V
Only carries a current if there is a fault
Safety wire to stop the appliance becoming live
Connected to the earth and to the casing
If the live wire touches the metal casing of the appliance, it will become live (you’ll get a serious electric shock if you touch it, as current flows through you to the ground)
Power
Energy transferred per second
Directly proportional to current and voltage
Power loss is proportional to resistance, and to the square of the current
Energy is transferred from chemical potential in batteries to electrical energy in wires to any form of useful energy in the devices they power
Energy transferred = Power multiplied time
Energy transferred = Charge × potential difference
The power, P, in watts W, the potential difference, V, in volts V, the current, I, in amperes A, and the resistance, R, in ohms Ω
Ways electrical energy may be transferred by appliances
Kinetic energy for a motor
Thermal energy in a kettle
Work done when charge flows through a circuit, and is also equal to energy transfer
Energy Transfers in everyday appliances
Ways electrical energy may be transferred by the appliance
Kinetic energy for a motor
Thermal energy in a kettle
Work done is when charge flows through a circuit, and is also equal to energy transferred, as all the electrical energy (ideally) gets transferred to the appliance
Power rating of an appliance shows the power it uses in Watts, so greater power rating means it uses more energy
The National Grid is a system of cables and transformers linking power stations to consumers across the UK
Electrical power is transferred from power stations to consumers using the National Grid
Transformers
1. Change the potential difference
2. Step-up Transformers increase the pd from the power station to the National Grid, so as the power is constant, current decreases so less energy is lost
3. Step-down Transformers decrease the pd from the National Grid to consumers for consumer safety
If a body has the same amount of positive and negative charge, they cancel out, forming a neutral body (i.e. protons and electrons in a neutral atom)
Like charges repel
Opposite charges attract
Insulators do not conduct electricity, their electrons cannot flow throughout the material, they are fixed
Conductors can conduct electricity, their electrons can flow, and are not fixed (they are delocalised)
Static Electricity occurs when two insulators are rubbed together, forming a positive charge on one object and a negative charge on the other
If conductors were rubbed, electrons will flow in/out of them cancelling out any effect, so they stay neutral
Sparking occurs when enough charge builds up, and the objects are close but not touching, the “spark” is when the charge jumps through the air from the highly negative object to the highly positive object, to balance out the charges
The charged objects experience a force – electrostatic force (of attraction/repulsion)