Resistors, lamps and diodes

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  • Created by: emews
  • Created on: 05-11-17 10:33
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  • Resistors, lamps and diodes
    • A resistor is an electrical component that restricts the flow of electric current
      • A graph of current against potential difference shows you how the current
    • When resistors are connected in series, the total resistance of two or more resistors is the sum of their individual resistance.
    • When resistors are connected in parallel, the combined resistance of two or more resistors is less than that of either resistor by itself.
    • Potentiometers are variable resistors with a resistance control that is adjusted once and then fixed.
    • filament lamp contains a thin coil of wire called the filament
    • This heats up when an electric current passes through it, and produces light as a result.
    • The resistance of a lamp increases as the temp increases
    • The current flowing through a filament lamp is not directly proportional to the voltage across it.
    • diodes
      • Diodes are electronic components which can be used to regulate the potential difference in circuits and to make logic gates
      • Very high resistance in one direction which means that current can only flow in the other direction,
      • LEDs and lamps
        • light-emitting diodes and lamps produce light when a current flows through them in the forward direction
        • LEDs and lapms are often used for indicator lights in electrical equipment, such as computers and televiion sets.
        • As LEDs use a much smaller current than other types of lighting, their use is increasing.
    • Thermistors and LDRs
      • Thermistors are used as temperature sensors, for example in fire alarms. The resistance decreases as the temperature increases
      • LDrs are used to detect light levels, for example in automatic security lights.
      • Their resistance decreases as the light intensity increases
    • Relays, capacitors and transistors
      • Relays may be used in circuits where it is not possible to have a direct electrical connection between the control circuit and the electrical components
      • A relay is a special type of switch turned on and off by an electromagnet.
      • When a current flows through the coil, an electromagnetic field is set up. The field attracts an iron armature, whose other end pushes the contacts together, completing the circuit.
      • When the current is switched off, the contacts open again, switching the circuit off. Relays are often used in circuits with thermistors and LDRs.
      • The circuit powering the coil is separate from the circuit switched on by the relay
      • A capacitor can store an electrical charge. Capacitors can be used to convert AC into DC. They can also be used to filter out fluctuations in a signal.
      • Transistors are tiny electronic switches and amplifiers.
        • Three main uses:
          • as an electronic switch within a circuit
          • to switch on another part of a circuit when a change in resistance is detected
          • to receive signals from low current devices and use these to turn on high current devices

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