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Lab: AC Circuits

Lab: AC Circuits. Integrated Science II. Applications of AC Circuits. AC (Alternating Current) vs. DC (Direct Current) Examples: Radio. Applications of AC Circuits. Examples: Alternator (AC generator). Applications of AC Circuits. Examples: Transformer.

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Lab: AC Circuits

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  1. Lab: AC Circuits Integrated Science II

  2. Applications of AC Circuits • AC (Alternating Current) vs.DC (Direct Current) • Examples: • Radio

  3. Applications of AC Circuits • Examples: • Alternator (AC generator)

  4. Applications of AC Circuits • Examples: • Transformer Used to step voltagesup or down-Exist in MOST devices!

  5. AC Circuit Elements • Resistors • Capacitors • Two conductors (plates) separated by a gap • Inductors (Solenoids) • Coils of wire • AC Power Supply (Function Generator)

  6. AC Circuit Elements • Resistors • Same elements as used for DC circuits • Ohm’s law still valid for AC currents • Voltage difference across a resistor with AC current flowing through it: • SI unit of resistance: Ohm (Ω)

  7. AC Circuit Elements • Capacitors (Energy Storage Devices!) • Two conductors (plates) separated by a gap, • One plate has +Q and the opposite has -QDefinition of capacitance:The ability of a body to store electric charge • Capacitance is a constant that only depends on plate geometry (shape, spacing,…) • SI unit of capacitance: Farad (F)

  8. Activity/Example: Parallel Plate Capacitor • Capacitance of a parallel plate capacitor: • Area of plate’s face = ASeparation distance between the plates = dε0 = 8.854 x 10-12 F/m = permittivity of free space • Use this formula to calculate the capacitance of a metal plate capacitor • Consider a plate measuring 6 in. by 6 in. • Calculate capacitance for d=0.2 mm and 2 mm • Which is a better storage device?

  9. AC Circuit Elements • CapacitorsStore energy in the electric field generated between the plates from the separation of (+) and (-) charges • Voltage difference across a capacitor in an AC circuit, means that the charges have potential energy. The stored energy turns out to be U = ½ CV2

  10. AC Circuit Elements • Inductors (Solenoids)- Energy is stored in a magnetic field due to the current, and this can prevent current from changing rapidly in some circuits. • Coils of wire-Current passing through generates magnetic field • Quantified by inductanceSI unit of inductance: Henry (H)

  11. Example:Inductance of a Solenoid • Consider a cylindrical solenoid that is 10.0 cm long, with a radius of 0.50 cm.Calculate the inductance of this coil, if it is also known that there are 200 turnsof copper wire in the solenoid. • Use the formula: • with μ0 = 4π x 10-7 H/m

  12. Example:Magnetic Field in a Solenoid Suppose the solenoid from the last example is connected to a DC power supply that passes 1.00 mA of current through its wires. What is the value of the magneticfield at the center of the solenoid? Use the formula: where the density of turns (turns per unit length) for the coil is given by

  13. Transformers and Mutual Inductance • Transformers on power poles step down the voltage before it goes into your house!

  14. AC Power Supply • Generates AC voltage wave (often sine wave)

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