Ohm's Law and Resistance Notes

Voltage and Current

• Voltage (V): Push that makes electric charges move, measured in volts (V).
  • Higher voltage = stronger push.
  • Example: 9V battery has a stronger push than a 1.5V battery.
• Current (I): Flow of electric charge, measured in amperes (A) or amps.
  • Example: Electric current flows through wires to light up a light.
• Voltage = push, Current = flow

Resistance

• Property of material that slows down electron flow and converts electrical energy into other forms.
• High resistance converts electrical energy into heat and light (e.g., light bulb filament).
• Low resistance allows electrons to travel with minimal energy loss (e.g., connecting wire).
• Smaller tube = more resistance = less current
• Resistance transforms electrical energy into other forms of energy, such as heat.

Ohm's Law

• Electrical resistance is the ratio of voltage to current, measured in ohms (\Omega).
• Formula: V = IR (Voltage = Current x Resistance)
• I = V/R
• R = V/I
• Voltage (V) = Volts
• Current (I) = Amps
• Resistance (R) = Ohms (\Omega)

Ohm’s Law - Practice

• Convert prefixes before calculating.

Converting Prefixes

• milli (m) = one-thousandth (e.g., 25 mA = 0.025 A)
• kilo (k) = one thousand (e.g., 5.0 k \Omega = 5000 \Omega)
• mega (M) = one million (e.g., 12 MV = 12,000,000 V)

Determining Resistance

• Method 1: Use a voltmeter to measure voltage and an ammeter to measure current; then use Ohm’s law to calculate.
• Method 2: Use an ohmmeter to directly measure resistance using its internal battery.

Resistors

• Electrical components with specific resistance values.
• Used to control current or potential difference in a circuit.

Resistor Colour Code

• Band 1: First digit of resistance.
• Band 2: Second digit of resistance.
• Band 3: Multiplier (power of 10 factor).
• Band 4: Accuracy (Gold 5%, Silver 10%, No colour 20%).