Electricity and Circuits Summary

Simple Circuits

• Review of current electricity.
• Current electricity is made of electric charges.
• Electric current is the flow of electric charges.
• Electrical appliances work by using electric current to perform tasks.
• Components:
  • Energy source (e.g., battery): supplies electrons with energy.
  • Energy user (e.g., light globe): converts and delivers energy.
  • Wires: complete the circuit.
• Open Circuits: broken, do not allow electron flow.
• Closed Circuits: complete, allow electron flow.
• Circuit components are represented by symbols in circuit diagrams.
• Series circuit:
  • All components are in a row.
  • One path for electricity.
  • If one light goes out, the entire circuit is broken.
• Parallel circuit:
  • Multiple paths for electricity.
  • If one light goes out, the others remain on.

Structure of an Atom and Ions

• Atom: consists of protons (+ve) and neutrons surrounded by electrons (-ve).
• Atoms are neutral because the number of protons equals the number of electrons.
• Ions: atoms that have gained or lost electrons.
• Cation: atom loses electrons à positive charge.
• Anion: atom gains electrons à negative charge.

Current

• Current: flow of electric charges.
• Requires a closed pathway (circuit) for electric charges to flow.
• Can be DIRECT (DC) or ALTERNATING (AC).
• DC: electrons flow in one direction (e.g., battery).
• AC: electrons shuffle back and forth (e.g., power points).

Current, Voltage, and Resistance

• Current: rate of flow of electric charge through a circuit.
  • Symbol: $I$
  • Unit: Amps (A).
  • Measured by an ammeter in series.
• Voltage: energy/force needed for electrons to flow.
  • Symbol: $V$
  • Unit: Volts (V).
  • Measured by a voltmeter in parallel.
• Resistance: opposition to the flow of electric current.
  • Symbol: $R$
  • Unit: Ohms ($\Omega$).
  • High resistance: difficult for electrons to pass through.
  • Low resistance: easy for electrons to pass through.
• Resistance of a wire depends on:
  • Type of material.
  • Length of wire.
  • Thickness of wire.
• Supply voltage: voltage differs between sources (e.g., mains voltage vs. dry cells).
• Transformers reduce voltage for devices (e.g., laptops).

Ohm’s Law

• Discovered in 1825 by Georg Simon Ohm
• Relates voltage (V), current (I), and resistance (R).
• Formula: $V = R \times I$

Practical Circuits: Series and Parallel

• Series circuit: components connected one after another in a single loop.
• Parallel circuit: multiple branches, each with its own components.
• Voltage:
  • Series: input voltage is divided among components.
  • Parallel: voltage across components equals the applied input voltage.
• Current:
  • Series: remains the same across all components.
  • Parallel: shared between the devices.
• Resistance:
  • Series: resistors are added to obtain equivalent resistance ($R<em>{eq} = R</em>1 + R<em>2 + R</em>3$).
  • Parallel: requires a specific formula for solution ($\frac{1}{R<em>{eq}} = \frac{1}{R</em>1} + \frac{1}{R<em>2} + \frac{1}{R</em>3}$).
• Limitations:
  • Series: a damaged component opens the entire circuit.
  • Parallel: a damaged component only opens that branch.

Motors and Generators

• Electric motors use magnets to create motion.
  • Permanent magnet: constant magnetic field.
  • Temporary magnet (electromagnet): magnetic field created by electric current.
• Generators use electromagnetism to generate electricity using:
  *Electric Wire coil
  *Magnet
  *Spinning movement
  *Generators convert kinetic (motion) energy into electricity.