Potential-Divide-and-Potentiometer.pptxp

Potential divider

1. 3 July 2015 Potential Dividers • Describe the action of a variable potential divider (potentiometer ) • recognize and show understanding of circuits operating as light-sensitive switches and temperature-operated alarms NB Answers in Notes section at bottom of each slide.

2. Resistance Recap Resistance (in ohms, Ω ) is a measurement of how difficult it for electric current to pass through any part of a circuit. What two measuring instruments would be required to calculate the resistance of this resistor? A V 2.0 A 12.0 V     Ω  

3. Series Circuit Recap A A A R 1 R 2 What is the total resistance of this circuit? Which ammeter would have the largest reading and why?

4. Series Circuit Recap R 1 R 2 What is the total resistance of this circuit? Which ammeter would have the largest reading and why? Calculate the current in this circuit. 3.0 V 6 Ω 6 Ω A

5. Series Circuit Recap R 1 R 2 What is the total resistance of this circuit? Which ammeter would have the largest reading and why? Calculate the current in this circuit. What is the reading on a voltmeter connected in parallel across both resistors and why? 3.0 V 6 Ω 6 Ω V

6. Series Circuit Recap R 1 R 2 What is the total resistance of this circuit? Which ammeter would have the largest reading and why? Calculate the current in this circuit. What is the reading on a voltmeter connected in parallel across both resistors and why? What is the reading on a voltmeter connected across one resistor and why? 3.0 V 6 Ω 6 Ω V

7. Series Circuit Recap R 1 R 2 What is the total resistance of this circuit? Which ammeter would have the largest reading and why? Calculate the current in this circuit. What is the reading on a voltmeter connected in parallel across both resistors and why? What is the reading on a voltmeter connected across one resistor and why? What is the reading on a voltmeter connected across the 2nd resistor and why? 3.0 V 6 Ω 6 Ω V

8. The potential divider circuit R 1 R 2 Calculate the current in this circuit. What will be the reading on a voltmeter connected across both resistors? 3.0 V 6 Ω 3 Ω V

9. The potential divider circuit R 1 R 2 Calculate the current in this circuit. What will be the reading on a voltmeter connected across both resistors? Calculate V 1 . 3.0 V 6 Ω 3 Ω V 1

10. The potential divider circuit R 1 R 2 Calculate the current in this circuit. What will be the reading on a voltmeter connected across both resistors? Calculate V 1 . Calculate V 2 . Explain why V 1 and V 2 are different 3.0 V 6 Ω 3 Ω V 2

11. The potentiometer A potentiometer is a single wire with a sliding contact that can be used to build a potential divide circuit. L V Investigate how the brightness of the bulb and the reading on the voltmeter change as the length L of the wire is changed. Explain the pattern obtained in terms of the potential divide circuit. R 2 R 1

12. BRIEF: We need a sensor where the voltage responds to the light intensity i.e. voltage should get larger as the light gets brighter V R 1 R 2 Problem . . . output The resistance of the LDR gets smaller as the light gets brighter . . . . . . so the voltage across R 1 gets smaller. Result: the output voltage gets smaller as the light intensity gets larger. V R 1 R 2 Problem solved!!! output The resistance of the LDR gets smaller as the light gets brighter... ...so the voltage across R 1 gets smaller… ...but the voltage across R 2 gets larger. Result: the output voltage gets larger as the light intensity gets larger.

13. The two circuits below include a buzzer that will sound if the voltage across is greater than 2.0 V. They also include a thermistor whose resistance gets lower as temperature increases. diskuss which of the two circuits will sound an alarm when it is too cold and why. diskuss which of the two circuits will sound an alarm when it is too hot and why . Why would it be useful to replace R 2 with a variable resistor be useful in both circuits? B R 1 R 2 output B R 1 R 2 output 3.0 V 3.0 V