DC vs AC Current Quiz

Direct Current (DC)

• Uniform in strength
• Batteries are a common example.
• Used in electronic devices with a battery power source.
• Used to charge batteries in rechargable devices like laptops and cell phones.
• Two types: Continuous and pulsating

Alternating Current (AC)

• Reverses direction
• Current periodically varies in time rate and direction
• Frequency: cycles per second or Hertz
  • Lighting: 60 Hertz
  • Motors: 25 Hertz
• Phasing: Single Phase or 3-phase
• Most households and offices use AC because it loses less power than DC and has fewer issues converting high voltage to low voltage using transformers
• AC can be transported over long distances
• Powers electric motors which power household appliances like fridges, dishwashers, and toasters.
• Also powers things connected to the mains like TVs or chargers for laptops and phones.

Direct Current (DC) vs. Alternating Current (AC)

• DC:
  • Fixed polarity
  • Steady or fluctuating
  • Steady value
  • Easier to measure: 1.5 volts
• AC:
  • Reverses polarity
  • Varies between reversals
  • Stepped up or down
  • Easier to amplify: 110V+

Electrical Circuits

• A complete conducting path carrying current from a source of electricity to and through some electrical device or load and back to the source.
• Types of circuits:
  • Closed Circuit: complete, continuous path
  • Open Circuit: broken, incomplete, disconnected (non-functional)
  • Series Circuit: same current flows through all components, current has only one path to take.
  • Parallel Circuit: components are arranged so that the current divides between them.
  • Short Circuit: condition resulting from bridging any part of a circuit with a conductor of very low resistance. Can cause wires to heat up and potentially cause fire.

Sources of Electricity

• Battery: Combination of two or more electric cells capable of storing and supplying direct current by electrochemical means.
  • Primary Batteries: Deliver electricity as soon as its parts are assembled, non-renewable.
  • Secondary / Storage Batteries: Electricity from some external source must pass through before it can deliver electric current. Used for emergency lighting, rechargeable.
• Generator: Machine which converts mechanical energy to electrical energy.
  • Alternating Current Generators / Alternators: Converts mechanical energy to electrical energy in the form of alternating current.
  • Direct Current Generators: Rotating machine that supplies electrical output with unidirectional voltage and current. Used for elevators, escalators, telecommunications, signal systems, and clock systems.
• Dynamo Electric Machines: Electrical generator that creates direct current using a commutator
  • Motors: machine that converts electrical energy to mechanical energy
  • Transformers: Machine for converting one voltage to another. Step-up transformer increases voltage, step-down transformer decreases voltage.
  • Rotary Converters: Changing alternating current to direct current and vice versa.

Conductors

• Materials or substances which allow electricity to flow through them.
• Humans and animals are conductors.
• Have free electrons on its surface which allow current to pass through easily.
• Transmit heat or light from one source to another.
• Examples: Copper, Brass, Steel, Gold, and Aluminum

Insulators

• Materials or substances which resist or don’t allow the current to flow through them.
• Do not have free electrons.
• Examples: Wood, cloth, glass, mica, quartz, plastic, rubber

Unit of Quantity

• Coulomb: SI unit of electric charge, equal to the quantity of electricity conveyed in one second by a current of one ampere. One coulomb is approximately 6.25 x 10^18 electrons.
• Ampere (I): Represents the rate of flow of one coulomb (6.25 x 10^18 electrons) per second through a given cross section.
• Ampacity: Current carrying capacity of a wire or cable expressed in Amperes.

Unit of Electric Potential

• Volt (V): Electrical unit of voltage or potential difference between two points in an electric field.

Unit of Electric Power

• Watt (W): Electric power; rate of doing electrical work.

Unit of Energy

• Watt-hours (Whr): Energy; capacity for doing work.

Unit of Resistance

• Ohm: Resistance that allows one ampere of current to flow when one volt is impressed upon it.
  • DC Circuit: ohm is called resistance (R).
  • AC Circuit: ohm is called impedance (Z).

Ohm's Law

• Relationship between Current, Voltage and Resistance:
  • Current in a DC circuit is directly proportional to the voltage and inversely proportional to the resistance of the circuit.
• Terms and Formula:
  • I = Current (Amperes), V = Voltage (Volts), R = Resistance (Ohms), W = Electric Power (Watts)
  • Formulas: I = V/R, V = IR, R = V/I
• Other equations: W = I^2R or VI, Whr = I^2R t