current

• Electrical current


  The rate of flow of electric charge
• When current flows, electrical work is done and energy transferred
• Charge


  Property of matter that causes a force when near another charge. Charge comes in two forms, positive and negative.
• One coulomb of charge is a package equivalent to 6,250,000,000,000,000,000 electrons
• Current


  The movement of charge through a conductor
• Types of current


  • Direct current
  • Alternating current
• Direct current


  The flow of electrons is consistently in one direction around the circuit
• Alternating current


  The direction of electron flow continually reverses
• Measuring current


  • Using an ammeter, which must be placed in series with the component
• One amp is the current that flows when one coulomb of charge passes a point in a circuit in one second
• If a current of 1.5 amps flows for 60 seconds

  90 coulombs of charge flow
• If a current of 13 amps flows for 10 seconds

  130 coulombs of charge flow
• If 10 coulombs of charge pass down a wire in 2 seconds

  The current is 5 amps
• Electrical current transfers energy around circuits
• Types of current


  • Direct
  • Alternating
• Electrical charge


  Moving electric charges, eg electrons moving through a metal wire
• Potential difference


  The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them.
• Resistor


  • Fixed-value resistors do not change their resistance, but with variable resistors it is possible to vary the resistance
• Bulb


  • A thin, high resistance wire that gets hot and glows when a current flows through it causing it to emit heat and light. Filaments are used in some types of bulb and electrical heaters.
• Diode


  • An electrical device that allows current to flow in one direction only
• Investigating current-voltage graphs


  1. Measure and observe current and potential difference

  2. Use appropriate apparatus and methods to measure current and potential difference for a resistor, bulb and diode
• For a fixed resistor


  The potential difference is directly proportional to the current
• Ohm's Law


  The rule that states that the current (I) flowing through a resistor (R) is directly proportional to the voltage (V) across the resistor, provided the temperature remains constant
• Resistance


  The opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms.
• Ohmic conductor


  A device that obeys Ohm's Law - potential difference and current are proportional, eg wire, resistor
• For a filament bulb

  The current does not increase as fast as the potential difference
• Vibrations


  Repeated movements back and forth (about a fixed point)
• Ions


  Electrically charged particle, formed when an atom or molecule gains or loses electrons
• Electrons


  Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons
• Semiconductor


  Insulating material doped with impurities to affect electron energy bands and therefore affect conduction properties
• For a semiconductor diode


  Only allows current to flow in one direction
• If the potential difference is arranged to try and push the current the wrong way (also called reverse-bias) no current will flow as the diode's resistance remains very large</b>
• Current will only flow if the diode is forward-biased
• When forward-biased, the diode's resistance is very large at low potential differences but at higher potential differences, the resistance quickly drops and current begins to flow
• Heating of the resistance wire can cause burns to the skin
• Do not touch the resistance wire whilst the circuits are connected and allow it time to cool