Grade 9 Science: Current, Voltage, Resistance, and Circuits

Electric Current

• Definition: Electric current is the flow of electric charge through a circuit.
• Symbol: $I$
• Unit: Ampere ($A$)
• Measurement Tool: Measured with an ammeter
• Key Memory Rule: Current = flow

Voltage

• Definition: Voltage, also called potential difference, is the difference in electrical potential energy per unit charge between two points.
• Symbol: $V$
• Unit: Volt ($V$)
• Key Memory Rule: Voltage = the push that drives charge

Electrical Resistance

• Definition: Resistance is the opposition to the flow of electric current.
• Symbol: $R$
• Unit: Ohm ($\Omega$)
• Core Principle: Higher resistance means less current for the same voltage.

Ohm's Law

• Formulas:
  • $V = I \times R$
  • $I = \frac{V}{R}$
  • $R = \frac{V}{I}$
• Variable Definitions:
  • $V$ = voltage
  • $I$ = current
  • $R$ = resistance

Series Circuits

• Path Configuration: A series circuit has one path for current.
• Key Characteristics:
  • Current is the same everywhere in the circuit.
  • Voltage is shared among components.
  • Adding resistors increases total resistance.
  • Circuit Failure Rule: If one component opens or breaks, the circuit stops working.

Parallel Circuits

• Path Configuration: A parallel circuit has two or more paths (branches) for current.
• Key Characteristics:
  • Current splits between branches.
  • Voltage is the same across each branch.
  • Adding another branch decreases total resistance.
  • Circuit Failure Rule: If one branch opens, other branches can still work.