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Chem. 133 – 2/6 Lecture

Chem. 133 – 2/6 Lecture. Announcements. Homework Set 1.1 – due today Quiz today Term Project Handout I have some additional possible projects related to a sustainable technology effort This will be placed near a term project sign up list in 516 Possible Schedule Change

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Chem. 133 – 2/6 Lecture

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  1. Chem. 133 – 2/6 Lecture

  2. Announcements • Homework Set 1.1 – due today • Quiz today • Term Project Handout • I have some additional possible projects related to a sustainable technology effort • This will be placed near a term project sign up list in 516 • Possible Schedule Change • I may have you attend scheduled research presentations by candidates for a new analytical chemist (3:30 to 4:30, late Feb. or early Mar.) in place of the first hour of lab. The lab schedule would be modified as a result.

  3. ElectronicsCapacitors Capacitors are devices to store charge capacitors are plates with small gap between plates charge spreads out along plate inducing opposite charge to other plate no dc current across gap (gap is non-conductive) 5 V Capacitance = C = q/V In capacitors, C = constant

  4. ElectronicsCapacitors Uses of Capacitors Storage of charge to provided needed power Power supply may not supply enough power to start motor (start up power > running power) with capacitor, initial available I is high motor

  5. ElectronicsCapacitors Use of Capacitors (continued) Analog data filter (RC filter – low pass type shown) signal out signal in Reduction of high frequency noise (example is numerically done filter)

  6. ElectronicsRC Circuits An RC circuit consists of a resistor and capacitor in series You are responsible for quantitative understanding of behavior from step change in voltage (see below) • Before t = 0, switch in down position so V = 0 all parts but short segment Switch 2) As switch is thrown (t = 0), charge travels through resistor to capacitor, but this takes time 5 V V = 5V 3) After some time, the capacitor is fully charged and current drops to zero

  7. ElectronicsRC Circuits Go to blackboard for more details of step change

  8. ElectronicsMore on RC Circuits • Application in Lab • when t(pulse period) >> RC, can treat as isolated step changes • VR quickly returns back to 0 and VC to VIn • when t(pulse period) ~ or < RC, can not treat as isolated step changes, and need to consider that VC changes slowly so will not reach Vin. • at the time of a step change to, VRo = Vin - VC and then later VR = (Vin - VC)e-t/RC at 10 ms, Vin -> -5V; VC = 3 V (not yet fully charged); VR = - 5V – 3V = -8V

  9. ElectronicsMore on RC Circuits For RC >> pulse time, it takes time for VC to become repetitive and a sawtooth wave results Calculation of t: DVC/Dt = (Vin – VC)/t or t = (Vin – VC)Dt/DVC = (-5 – 0.5V)(10 ms)/-0.91V = 60 ms (at 130 ms)

  10. Electrical MeasurementSome coverage in Ch. 17 Covers: How meters work Errors in measurements Most common measured quantities: Voltage Current Resistance Others (capacitance, frequency, etc.)

  11. Electrical MeasurementThe Ammeter An analog measurement Meters respond only to current Now less common than voltmeters Will not cover in detail Current produces magnetic field to deflect needle

  12. Electrical MeasurementDigital Voltmeter Main Components Analog to digital convertor Memory for data storage Data display (decimal readout) Circuits for converting R, I measurements to V measurements (for “multimeters”) Analog vs. Digital Analog has continuously variable vs. discrete values for digital Analog resolution based on needle and scale, digital resolution based on number of display digits (or on number of bits of A/D convertor) 4 3 7

  13. Electrical MeasurementDigital Voltmeter - Binary Digital Electronics can be understood better by using binary math In binary, only two possibilities exist: 0 1

  14. Electrical MeasurementBinary and Bits Counting in binary Number of digits = # bits = # parallel wires

  15. Electrical MeasurementBinary to Decimal Conversion (and visa versa) Go to blackboard

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