Turn up the heating The electric current Heating effects of a current Voltage – Current graphs.

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AS Level Electricity - Circuits

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Presentation transcript:

Turn up the heating The electric current Heating effects of a current Voltage – Current graphs

Electric current (I) What is an electric current? An electric current is a flow of charges and it is measured in amperes (A). An electric current through a circuit is similar to water running through a system of pipes. Describe the features of an electric current that this model cannot explain. Hint: what happens if you cut the water pipe? If we cut the water pipe the water still runs out, but cutting a wire in the circuit breaks the circuit and the electric current stops flowing.

Heating effects of a current Choose the component that for a given current will get hotter than the others. Resistor Diode Filament lamp

Resistors For relatively low currents the resistor stays at constant temperature and its resistance does not change. I V For this value of the current the resistance is constant and the temperature does not rise. Back

Diodes The current increases at higher and higher rates, so the resistance gets lower. I V For this value of the current the resistance is lower and the diode does not get hot. Back

Filament lamps The current decreases at higher and higher rates, so the resistance gets higher. I V For this value of the current the resistance is higher and the filament inside the lamp gets hotter. Back

Heating effects of a current If we keep the same current flowing through a circuit and we change the resistance, the higher the resistance, the hotter the component. Which of these wires will get hotter when the same current flows through them?

Heating effects of a current If we keep the same current flowing through a circuit and we change the resistance, the higher the resistance, the hotter the component. Which of these wires will get hotter when the same current flows through them?

Voltage – Current graphs What does the gradient of this graph represent? The gradient of a V – I graph is the resistance I V The gradient of the line is V/I, but R = V/I Gradient = Resistance

Voltage – Current graphs So if you calculate the gradient of the graph you have found the resistance! I (A) V (V) Calculate the gradient of this graph Gradient = 5 volts 6 amps = 0.83 ohms