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 voltages up 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 -Q Definition 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 = A Separation distance between the plates = d ε0 = x 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
Capacitors Store 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 inductance SI 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 turns of 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 magnetic field 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)