Ohm's Law, Electric Measurement, and Incandescent Objects

• Electric currents exceeding ~10 mA passing through the body can be dangerous

Ohm's Law and Equations

• Ohm's law states that the electric current flowing through a conductor is proportional to the voltage across it
• The equation for Ohm's Law is I = V/R or V = I x R
• Power, measured in watts (SI unit), is defined as P = V x I
• Using Ohm's law, power can also be expressed as P = I² x R or P = V² / R

Electrical Measurement Instruments

• When using a voltmeter, it needs to be connected in parallel with the resistor or device being measured
• When using an ammeter, it needs to be connected in series with the resistor or device being measured

Halogen Lamps

• In a halogen incandescent lamp, the halogen gas recycles evaporated tungsten back onto the filament

Incandescent Objects

• As the temperature of an incandescent object increases:
  • The intensity of emitted energy increases
  • The spectrum of energy emission shifts to shorter wavelengths, moving from red to blue in the visible spectrum

Kirchhoff's Laws

• Kirchhoff's Current Law (KCL) states that the total current entering a node in a circuit equals the total current leaving that node
• Kirchhoff's Voltage Law (KVL) states that the sum of the electrical potential differences around any closed circuit loop equals zero

Electrical Power Transmission and Faraday's Law

• Electric power is delivered more efficiently at higher voltages because this reduces the current, lowering resistive losses in transmission wires
• Faraday's law explains that a changing magnetic flux induces a voltage across the terminals of a nearby wire coil
  • The induced voltage is proportional to the rate of change of the magnetic flux and the number of turns in the wire coil
  • Equation: emf = -N dΦ/dt

Transformers

• The relationship between voltages and turns in a transformer is Vs/Vp = Ns/Np

Sinusoidal AC Signals

• For a sinusoidal AC signal: Vrms = (Vamplitude) / √2,
• Vrms = 0.707 x Vamplitude
• Understand time, period, amplitude, and peak-peak voltage.

Light Sources

• Low-pressure sodium lamps are efficient because they emit light close to the human eye's peak sensitivity for color vision
• Fluorescent lamps use mercury vapor and a phosphorescent coating to convert UV light into visible light

Photoresistors

• When light strikes a photoresistor, the resistance of the semiconducting material decreases
  • Brighter light causes a greater reduction in resistance.

Silicon Diodes

• Silicon diodes need a forward bias voltage of 0.6 - 0.7 V to allow significant current flow
• A forward-biased silicon diode can be modeled as a 0.7 V voltage drop with no resistance.
• Vd ≈ 0.7 V
• VR ≈ VS - 0.7 V

Stepper and Electric Motors

• Stepper motors can be controllably stopped and held at designated positions
• Electric motors and generators are duals of each other

BJTs

• A BJT transistor is controlled by the voltage between its base and emitter
  • For an NPN transistor to be in forward bias: VB ≈ VE + 1
  • For a PNP transistor to be in forward bias: VB ≈ VE

Learn about electric currents and their dangers, Ohm's Law and related equations for power. Understand the use of voltmeters and ammeters in electrical measurements. Explore halogen lamps and the properties of incandescent objects as temperature increases.