Electric Current: Physics Chapter 23

• Chapter 23 concerns electric current

Flow of Charge

• Electrons are responsible for the flow of charge.
• Charge flows when a potential difference exists between two points in a conductor.
• Electrons move from high to low potential, equivalent to negative to positive.
• Electron flow is opposite to conventional current direction.
• Maintaining a potential difference allows continuous charge flow.
• Static shocks arise from potential differences and are quickly balanced.

Electric Current

• Electric current is the rate of charge flow.
• Conduction electrons move freely through a fixed atomic lattice.
• Protons remain bound within the nuclei of lattice atoms and do not contribute to the flow.
• Electric current is measured in Amperes [A].
• 1 Ampere [A] equals 1 coulomb of charge per second.
• Electric current measures the number of electrons passing through a circuit each second.
• Amperage refers to the rate of electron flow.
• Lower amps mean fewer electrons pass through the wire each second.
• Compute current by dividing charge by time.

Voltage

• Voltage, or potential difference, is measured in volts.
• Potential difference is supplied by voltage sources, such as batteries and generators.
• Voltage provides the force to move electrons through a circuit.
• A voltage source functions as an electron pump.

Electrical Resistance

• Electrical resistance opposes charge flow.
• Conductivity indicates how easily charge flows through a material.
• Larger wires typically have lower resistances.
• Current on a circuit depends on both voltage across elements and electrical resistance, measured in ohms (Ω).
• Resistors regulate current inside electrical devices
• Wire composition affects resistance.
• Longer wires offer more resistance.
• Thicker wires offer less resistance.
• High temperature induces more resistance, proportional to temperature.
• Superconductors are maintained at very low temperatures.

Ohms Law

• Ohm measures electrical resistance.
• Ohm's Law relates or equates current, voltage, and resistance.
• The formula is V = I x R.

Electric Shock

• Electric shock is caused by current passing through the body
• Damage depends on the current and voltage applied, along with the body's resistance.
• Body resistance ranges from 100 to 500,000 Ω.
• Current [A] Effects:
  • 0.001 - Perceptible
  • 0.005 - Painful
  • 0.010 - Involuntary muscle spasms
  • 0.015 - Loss of muscle control
  • 0.070 - Cardiac disruption (may be fatal after 1 second)

Electric Power

• Electric power measures the conversion rate of electric energy into other forms, such as mechanical, heat, or light.
• Watts [W] are the units of measure
• Power is current multiplied by voltage: P=IxV
• Using ohms law power can also be expressed as P = I(IxR)= IxR

Types of Current

• Direct Current (DC) flows in one direction, and voltage remains constant.
• Alternating current (AC) periodically changes direction.
• Electrons oscillate around fixed positions.
• Generators or alternators produce AC by periodically switching the sign on a driving voltage.

Converting Current

• In the U.S., AC frequency is 60Hz, or 60 cycles per second.
• Converting AC to DC involves using a diode, which allows current flow in only one direction.
• When the input to a diode is AC, the output is DC.
• If a capacitor is discharging and charging: the current will be smooth
• Extra diodes remove gaps in voltage output or reverse polarity.

Additional Facts

• Incandescent light bulbs (ILB) dissipate most of their energy as heat, not light.
• Light emitting diodes (LED) are more efficient and last longer as light sources.
• ILB: 95% of energy as heat, 5% as light
• LED: 65% as heat, 35% as light
• Electrons typically move randomly, with randomness canceling out motions and resulting in no current flow
• Applying voltage gives order to motion and provides current.
• Average electron speed is in the millions of km per hour.