Electrical Circuits

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In a circuit, current is the flow of charge.

It can be measured in coulombs per second where 1 C / s = 1 amp.

The electrons actually flow from negative to positive

Current (A) = Charge (C) / time (s) I = Q / t

They are vibrating about randomly inside the metal very quickly but they drift though the wire very slowly.

Current is large cos there are a LOT of electrons flowing, not cos they travel quickly.

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Amount of energy transferred per coulomb is called the voltage or potential difference (p.d.)

1 Volt = 1 Joule per Coulomb (1JC )

Voltage (V) = Energy Transferred (J) / Charge (C) V = W / Q

Through a bulb this energy is transferred into other forms, e.g. heat and light.

Power (W) = Energy Transferred (J) / time (s) P = W / t

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Greater the resistance then the bigger the voltage needed to make a certain current flow.

Resistance (Ohms) = Voltage (V) / Current (A) R = V / I

Components can vary, e.g. the resistance of a bulb gets bigger when the bulb gets hotter

When resistance is fixed then voltage and current are proportional.

Conductance (S) = Current (A) / Voltage (V) G = I / V

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