Electric current Electric current is a flow of charge In metallic conductors, the charge is carried by electrons

Where do these electrons come from? Electrons are in the circuit Insulators do not have free electrons

Chemical reactions in the battery supply the energy to move the electrons All electrons in the circuit feel the effect of the battery – action at a distance

Electrons are free in the conductor Thermal motion – 1000’s meters per second Drift velocity caused by battery – millimeters per second

Electrons collide with atoms and ions - energy is converted into other forms The amount of energy converted depends on the nature of the conductor

The drift of electrons is the electric current Convention – electric current is from plus to minus Ions carry charge in cells and solutions of electrolytes

Voltage Voltage = Potential difference Voltage is a measure of ENERGY Voltage of battery is the energy available for each unit of charge. 6 V means that there are 6 J of energy for each unit of charge

Voltage across a resistor is the energy being converted by each unit of charge in the resistor The greater the resistance at a point, the greater the fraction of the total energy that is converted at that point. Principle of Conservation of Energy applies.

6V 4 V 2 V 20 Ω 10 Ω 2 joules of energy are converted for each coulomb 6 joules of energy are transferred to each coulomb from the battery 4 joules of energy are converted for each coulomb

6V 6 joules of energy are transferred to each coulomb from the battery 6 V Each coulomb is giving up 6 joules of energy If there was only one component, e.g. a bulb, in the circuit, all 6 joules would be converted there.

The more items that are in a series circuit, the less energy will be converted in each, as there are only 6 joules to be shared between them The energy is converted in direct proportion to the size of the resistance

In a parallel circuit, all the components convert the same amount of energy from each unit of charge that passes through them i.e. the amount it receives from the 6 V battery - 6 J The potential difference (voltage) between the ends of each component is the same - 6 V

In a parallel circuit, there will be different currents flowing through the components if they have different resistances.

6 joules of energy are converted for each unit of charge I = I 1 + I 2 6 joules of energy are converted for each unit of charge 6 joules of energy are transferred from the battery to each unit of charge 6 V I I1I1 I2I2

Remember For different value resistors in series –same current, different voltage in parallel –same voltage, different current

Resistance Opposition to current in a metallic conductor depends on length cross-sectional area material

R must not be in a working circuit Ω Ohmmeter R

The Multimeter COM VΩmA 10A DC OFF V Ω A V DISPLAY 10A