Electricity and Magnetism

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    • There are two types of charges, positive and negative charges
    • Unlike charges attract and like charges repel
    • Adding a charge to something involves the addition or removal of electrons
    • Current is related to the flow of charge
    • Current in metals is due to a flow of electrons
    • The potential difference across a circuit component is measured in volts
    • The electromotive force of an electrical source of energy is measured in volts
    • V=IR
      Potential Difference = Current multiplied by Resistance
    • For a parallel circuit, the current from the source is larger than the current in each branch
    • The combined resistance of two resistors in parallel is less than that of either resistor by itself
    • The current from the source is the sum of the currents in the separate branches of a parallel circuit
    • The sum of the potential differences across the components in a series circuit is equal to the total potential difference across the supply
    • Electric charge is measured in units called coulombs
    • An ammeter measures the current in a circuit and is connected in series
    • Conventional current flows in the direction opposite to that which electrons flow in.
    • Red = Conventional Current
      Green = flow of electrons
    • The energy supplied by the source in driving a unit charge around a circuit.
    • The maximum voltage a cell can produce is called the electromotive force (EMF), measured in volts.
    • The current at any point in a series circuit is the same
    • The current splits at each branch in a parallel circuit so the total current is always greater than the current in one branch
    • In parallel: Current across the source = sum of currents in the separate branches
    • Electrostatic repulsion is caused by the force between charges. When the charges are the same, they repel each other.
    • In experiments showing the production of electrostatic charges by friction, insulating solids like plastics are given a charge. This is done using friction to transfer electrons from the surface. By removing negative electrons, the insulator is left with a positive charge.
    • A charged object creates an electric field around itself. This can be shown by electric field lines.
    • Electric field lines always point away from positive charges and towards negative charges
      A) +
      B) -
      • The strength of an electric field depends on the distance from the object creating the field:
      • The field is strongest close to the charged object - this is shown by the field lines being closer together
      • The field becomes weaker further away from the charged object - this is shown by the field lines becoming further apart
    • Objects in an electric field will experience an electrostatic force
    • The force of an electrostatic force is either attractive or repulsive depending on whether the charges are opposite (positive and negative) or the same (positive and positive)
    • Fields lines always go away from positive charges and towards negative charges – they have the same direction as the direction of the force on a positively charged particle at a point in that field
    • The electric field between two parallel plates is a uniform electric field.
      The field lines are:
      • Directed from the positive to the negative plate
      • Parallel
      • Straight lines
    • Conductors allow charge carriers to freely move
    • Insulators do not allow charge carriers to move
    • conductor is a material that allows charge (usually electrons) to flow through it easily
      Examples of conductors are:
      • Silver
      • copper
      • Aluminium
      • Steel
      Conductors tend to be metals
    • An insulator is a material that has no free charges, hence does not allow the flow of charge through them very easily
      Examples of insulators are:
      • Rubber
      • Plastic
      • Glass
      • Wood
    • The current is the amount of charge passing a point in a circuit every second
    • Q = I × t
      Charge = Current × Time
    • Charge is measured in coulombs
    • Current is measured in amps
    • The electromotive Force (e.m.f.) is the name given to the potential difference of the power source in a circuit
    • The EMF of a circuit is defined as The electrical work done by a source in moving a unit charge around a complete circuit
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