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RESISTORS

RESISTORS. Always remember…… V = IR (V= voltage in volts; I = current in amps; R = resistance in ohms). Special types of resistors. Diodes. A diode is a device which allows current to flow only in one direction. It is also known as a rectifier This is what a diode looks like.

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RESISTORS

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  1. RESISTORS Always remember…… V = IR (V= voltage in volts; I = current in amps; R = resistance in ohms)

  2. Special types of resistors

  3. Diodes • A diode is a device which allows current to flow only in one direction. • It is also known as a rectifier • This is what a diode looks like

  4. Diodes • This is the circuit symbol for a diode • Draw this symbol in your books • The arrow on the symbol shows the direction the current can flow.

  5. Diode • If the diode is reversed it acts like a very high value resistor and prevents current flow.

  6. Diode • Uses of diodes • Protecting equipment should the power be connected the wrong way round, • Converting a.c. into d.c.

  7. Light dependent resistor The LDR

  8. LDR • This is a resistor whose resistance depends on the amount of light falling on it.

  9. LDR • This is the circuit symbol for a diode • Draw this symbol in your books • The arrows represent light falling on the LDR

  10. LDR • When light falls on an LDR its resistance falls rapidly. • In low light or the dark – they act as high resistors. • In bright light they offer very little resistance Resistance of an LDR Light level

  11. LDR • LDR’s can be used to switch on street lights when light falls.

  12. Thermistors Temperature-dependent resistors

  13. Thermistor • This is a resistor whose resistance depends on the temperature.

  14. Thermistors • This is the circuit symbol for a thermistor • Draw this symbol in your books

  15. Thermisitors • Thermistors are used in circuits which are designed to be controlled by temperature, such as a sprinkler system.

  16. Investigating thermistors Temp Volts Amps Resistance oC V A ohms Calculate the resistance at 5 different temperatures

  17. Plot a graph of resistance against temperature for your thermistor.

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