Module 4 definitions

• Conductors

  A material that allows the flow of electrical charge. Good conductors have a larger amount of free charge carriers to carry a current.
• Conservation of Charge
• Conventional Current

  The flow from positive to negative, used to describe the direction of current in a circuit.
• Coulomb

  The unit of charge.
• Electric Current

  The rate of flow of charge in a circuit.
• Electrolytes

  Substances that contain ions that when dissolved in a solution, act as charge carriers and allow current to flow.
• Electron Flow


  The opposite direction to conventional current flow. Electrons flow from negative to positive.
• Elementary Charge

  The smallest possible charge, equal to the charge of an electron.
• Insulators

  A material that has no free charge carriers and so doesn't allow the flow of electrical charge.
• Kirchhoff's First Law

  A consequence of the conservation of charge. The total current entering a junction must equal the total current leaving it.
• Mean Drift Velocity

  The average velocity of an electron passing through an object. It is proportional to the current, and inversely proportional to the number of charge carriers and the cross-sectional area of the object.
• Quantisation of Charge
• Semiconductors

  A material that has the ability to change its number of charge carriers, and so its ability to conduct electricity. Light dependent resistors and thermistors are both examples.
• Diode


  A component that allows current through in one direction only. In the correct direction, diodes have a threshold voltage (typically 0.6 V) above which current can flow.
• Electromotive Force

  The energy supplied by a source per unit charge passing through the source, measured in volts.
• Filament Lamp


  A bulb consisting of a metal filament, that heats up and glows to produce light. As the filament increases in temperature, its resistance increases since the metal ions vibrate more and make it harder for the charge carriers to pass through.
• 1. V Characteristics


  Plots of current against voltage, that show how different components behave.
• Kilowatt-Hour


  A unit of electrical energy. It is usually used to measure domestic power consumption.
• Light-Dependent Resistor


  A light sensitive semiconductor whose resistance increases when light intensity decreases.
• Negative Temperature Coefficient Thermistor

  A thermistor whose resistance decreases as temperature increases.
• Ohm


  The unit of resistance.
• Ohmic Conductor


  A conductor for which the current flow is directly proportional to the potential difference across it, when under constant physical conditions.
• Ohm's Law


  The current and potential difference through an ohmic conductor held under constant physical conditions are directly proportional, with the constant of proportionality being resistance.
• Potential Difference


  The difference in electrical potential between two points in a circuit. It is also the work done per coulomb to move a charge from the lower potential point to the higher potential point. It is measured in Volts.
• Power


  The rate of energy transfer in a circuit. It can be calculated as the product of the current and the potential difference between two points. It is measured in Watts.
• Resistance


  A measure of how difficult it is for current to flow through a material.
• Resistivity


  A measure of how difficult it is for charge to travel through a material. It is proportional to the object's resistance and cross-sectional area, and inversely proportional to the object's length. It is measured in Ohm metres.
• Resistor


  A device that has a fixed resistance and follows Ohm's law.
• Volt


  The unit of potential difference.
• Conservation of Energy
• Internal Resistance


  The resistance to the flow of charge within a source. Internal resistance results in energy being dissipated within the source.
• Kirchhoff's Second Law


  A consequence of the conservation of energy. The sum of the voltages in any closed loop must equal zero.
• Lost Volts


  The difference between a source's emf and the terminal voltage. It is equal to the potential difference across the source's internal resistance.
• Parallel Circuit


  Components are said to be connected in parallel when they are connected across each other (separate loops).
• Potential Divider


  A method of splitting a potential difference, by connecting two resistors in series. The total potential difference is split in the ratio of their resistances.
• Resistors in Parallel


  The potential difference across resistors connected in parallel is identical for each resistor. The current is split between the resistors. The total resistance is equal to the inverse of the sum of the inverses of the resistances of the resistors.
• Resistors in Series


  The current through resistors connected in series is identical for each resistor. The potential difference is split in the ratio of their resistances. The total resistance is equal to the sum of the resistances of the resistors.
• Sensor Circuits


  A circuit that reacts to external conditions. They commonly involve a semiconductor connected in a potential divider arrangement.
• Series Circuit


  Components are said to be connected in series when they are connected end to end (in one loop).
• Terminal PD


  The potential difference across the terminals of a power source. It is equal to the source's emf minus any voltage drop over the source's internal resistance.