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LOCKERBIE ACADEMY PHYSICS DEPT

LOCKERBIE ACADEMY PHYSICS DEPT

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LOCKERBIE ACADEMY PHYSICS DEPT

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  1. LOCKERBIE ACADEMY PHYSICS DEPT Nat 5 PHYSICS ELECTRICITY & ELECTRONICS

  2. LOCKERBIE ACADEMY PHYSICS DEPT Ways to work out voltage divider circuits. Follow the plan below:

  3. LOCKERBIE ACADEMY PHYSICS DEPT 1. Identify the component (the input device) 2. Set the conditions 3. Decide what happens to the resistance • Work out the effect of the voltage across the component 5. Find the effect on Vout 6. Find the effect on the transistor (include the magic number) 7. Find the effect on the output device

  4. Vs M V 0V LOCKERBIE ACADEMY PHYSICS DEPT

  5. Vs M V 0V 1. Identify the component LDR

  6. Vs M V 0V 2. Set the conditions As light increases

  7. Vs M V 0V 3. Decide what happens to the resistance As light increases RESISTANCE decreases

  8. Vs M V 0V • Work out the effect of the voltage across the component As resistance decreases voltage across the LDR decreases

  9. Vs M V 0V 5. Find the effect on Vout As VLDR decreases Vout increasesas they are not the same

  10. Vs M V 0V 6. Find the effect on the transistor (include the magic number) As Vout increases the voltage will increase above 0.7V (the magic number), the transistor will switch on current will flow between the emitter and collector and the motor will be on.

  11. Vs M V 0V 7. Find the effect on the output device Current will flow between the emitter and collector and the motor will be on.

  12. Vs M V 0V 2. Set the conditions 1. Identify the component 3. Decide what happens to the resistance • Work out the effect of the voltage across the component 5. Find the effect on Vout 6. Find the effect on the transistor (include the magic number) 7. Find the effect on the output device

  13. Vs M V 0V How this circuit works LDR As light increases RESISTANCE decreases Voltage across the LDR decreases As VLDR decrease Vout increases as they are not the same As Vout increases the voltage will increase above 0.7V (the magic number), the transistor will switch on. Charge will flow between the emitter and collector and the motor will be on

  14. Vs t V 0V Now try this one yourself

  15. Other TRANSISTORS • N-channel enhancement MOSFETS work in a similar way but the SWITCHING VOLTAGE is 1.8V

  16. Past Paper Q