P3: Electric Circuits

P3: Electric Circuits

1. Circuits

   • Current
     • Electric current is the rate of flow of electrical charge, which will only flow if a circuit is closed and if there is a source of potential difference E.G. battery.
   • Charge Equation
     • Charge (coloumbs, C) = Current (A) x Time (s)
   • Symbols

2. Resistance Equation

   • Resistance = Potential Difference (V) / Current (A)
   • Can use this for whole circuits or individual components

3. Energy & Power in Circuits

   • An electrical current transfers energy from a power supply (batteries, cells etc). A power supply works on a charge and transfers energy to it, and charges transfer energy to a component as they pass through it, by going against the resistance of the component.
   • Equations
     • Potential Difference = Work Done (Energy Transferred) / Charge
     • Energy Transferred (Work Done) = Charge x Potential Difference
     • Power (W) = Energy (J) / Time (s)
     • Power (W) = Potential Difference (V) x current (A)

4. Magnetic Field

   • All magnets have 2 poles - North and South pole. They produce a magnetic field (a region where other magnets feel a force), which can be shown by drawing magnetic field lines which go from the north to the south pole.

5. The Motor Effect

   • When a wire is put near a magnet, the two magnetic field interact with each other, which causes a force to be exerted on both the wire and the magnet. It usually causes the wire to move. The wire has to be at a right angle to the magnetic field, because the force reacts the best when it is like this
   • Force Equation
     • Force (N) = Magnetic Field Strength (T) x Current (A) x length of conductor (m)

6. Transformers

   • They have a size of the potential difference of an alternating current. They have 2 coils of wire and an iron core. When an alternating current is applied through one of the coils, it creates an alternating magnetic field.
   • Step Up Transformer
     • Potential difference goes up.
   • Step Down Transformer
     • Potential difference decreases

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