3. What we are going to achieve today 1)Using an Oscilloscope demo 2)Potential Dividers as control circuits 3)Revision and extension of work done so far; ready for the test.
4. Oscilloscopes A quick Demo and Explanation Next lesson you will use one as a voltmeter for an AC signal Name That Tune!
6. Deriving the Equation Current through the R1 and R2 I = V/R I = Vin / (R 1 + R 2 ) Voltage across R 1 V = I R 1 V = Vin (R 1 / (R 1 +R 2 ) ) Voltage across R 2 V out = I R 2
7. Uses of potential dividers When it is warm the thermistor has a low resistance When will Vout be high? When will Vout be low? R Thermistor What could this circuit be used for? R is set to be the average resistance of the thermistor’s resistance
8. Uses of potential dividers When it is warm the thermistor has a low resistance When will Vout be high? When it is warm When will Vout be low? When it is cold R Thermistor What could this circuit be used for? Control the speed of a fan R is set to be the average resistance of the thermistor’s resistance
9. Photodiode When it is dark the photodiode has a high resistance What could this circuit be used for? When is Vout high? When is Vout low? R is set to be the average resistance of the LDR’s resistance
10. Photodiode When it is dark the photodiode has a high resistance What could this circuit be used for? Control street lights When is Vout high? When it is dark When is Vout low? When it is light
11. Variable resistor 9 Volts R Variable resistor R is set to be the average resistance of the variable resistor’s resistance The variable resistor can be adjusted to change the resistance. What could this circuit be used for?
12. Variable resistor 9 Volts R Variable resistor R is set to be the average resistance of the variable resistor’s resistance The variable resistor can be adjusted to change the resistance. What could this circuit be used for? Volume control Dimmer Switch Shower Temperature The person is the feed back device
13. Revision and Extension Topics we have covered so far Lesson one (charge carriers) What is an electric current? How can we calculate the charge flow in a circuit? What are the charge carriers? What do we mean by potential difference? How can we calculate electrical power? What is resistance heating? How do energy transfers take place in electrical devices? Lesson two (potential differnce) How does the current through a filament lamp vary with pd? What are the characteristics of a diode? When can we use Ohm’s law? Lesson three (resistivity) What causes electrical resistance? What is a superconductor? What can we use thermistor for? Lesson four (resistors) What are the rules for series and parallel circuits? How do we use the rules in circuits? What are the principles behind these rules? How do we calculate currents in circuits with; resistors in series and parallel?
15. Lesson One Charge carriers – can be electrons or ions (positively or negatively charged atoms) Charge is a property of charge carriers ∆ Q = I ∆ t e = 1.6 x 10 C V = IR The coulomb is defined as equal to the charge flow in one second when the current is one Ampere. C = A s (Q = I t) The definition of the volt is work done per coulomb of charge transferred between two points V = W/Q
16. Lesson Two 1) P=VI, 2)P= I 2 R , 3)P =V 2 / R Power in electrical circuits can be found by Power is measured in Watts Work in an electrical circuit W =IV∆t Lesson three Resistivity Lesson four Rt =R1 + R2 +R3
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18. Mission impossible Enter the code to stop the bomb Find the answer to all these questions to find the 6 digit code
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