Ohm's Law

Series Introduction to Electrical Physics

• Introduction to the series on electrical physics basics, covering key topics:

  • Ohm's Law

  • Series Circuits

  • Parallel Circuits

• Focus of this lesson: Ohm's Law and its relationship with voltage, resistance, and current.

OHM'S LAW

• Definition: Ohm's Law describes the relationship between voltage (V), resistance (R), and current (I) in an electrical circuit.

• Ohm's Law Equation:

  • Current (I) is directly proportional to Voltage (V) and inversely proportional to Resistance (R).

  • Mathematically:
    $I \propto V \quad \text{and} \quad I \propto \frac{1}{R}$

Importance of Ohm's Law

• Understanding Ohm's Law is crucial for analyzing circuit diagrams and solving for missing variables.

• Definitions of key terms:

  • Voltage (V): The force that pushes electrons through a circuit.

  • Resistance (R): The attribute that slows down the flow of electrons.

  • Current (I): The rate at which electrons flow through a circuit.

Ohm's Law Formulas

• Three formulas derived from Ohm's Law:

  • Voltage: $V = I \times R$

  • Resistance: $R = \frac{V}{I}$

  • Current: $I = \frac{V}{R}$

Utilizing Ohm's Triangle

• Ohm's Triangle: A tool to help determine which formula to use.

  • Layout:

  • V (Voltage) at the top

  • I (Current) at the bottom left

  • R (Resistance) at the bottom right

  • Format:

  • Letters separated by lines

Determining Which Formula to Use

1. Input Method: Insert numbers provided for two variables and solve for the missing variable.

2. Visual Method: Cover the letter representing the variable you are solving for.

   • Example: Solving for resistance (R)

   • Cover R in the triangle, leaving V and I.

   • The relation shows $V \div I = R$.

Relationship Between Variables

• Resistance and Current Relationship:

  • As resistance increases, current decreases.

  • More resistance encountered by voltage reduces electron flow speed.

• Resistance and Voltage Relationship:

  • As resistance increases (assuming current constant), voltage increases.

  • Increased resistance necessitates increased force to maintain electron flow.

Analogy for Understanding

• Hypothetical Scenario:

  • Water Flow Analogy:

  • A pump pushing water through pipes:

  • Bigger pump = higher pressure (voltage) to move water (current)

  • Narrow pipes = more resistance, slowing down water flow

  • Wider pipes = less resistance, allowing freer flow of water.

Practice Problem on Finding Voltage

• Given:

  • Circuit has a battery and single resistor.

  • Current (I) = 4 amps

  • Resistance (R) = 3 ohms

• Find Voltage (V).

  • Using Ohm's Triangle: Cover V.

  • Remaining variables: I and R

  • Calculation:

  • $V = I \times R = 4 \text{ A} \times 3 \text{ ohms} = 12 \text{ volts}$.

Practice Problem on Finding Resistance

• Given:

  • Circuit has a battery and single resistor.

  • Voltage (V) = 15 volts

  • Current (I) = 5 amps

• Find Resistance (R).

  • Using Ohm's Triangle: Cover R.

  • Remaining variables: V and I.

  • Calculation:

  • $R = \frac{V}{I} = \frac{15 \text{ V}}{5 \text{ A}} = 3 \text{ ohms}$.

Practice Problem on Finding Current

• Given:

  • Circuit with battery and single resistor.

  • Voltage (V) = 30 volts

  • Resistance (R) = 6 ohms

• Find Current (I).

  • Using Ohm's Triangle: Cover I.

  • Remaining variables: V above R.

  • Calculation:

  • $I = \frac{V}{R} = \frac{30 \text{ V}}{6 \text{ ohms}} = 5 \text{ amps}$.

Summary of Ohm's Law

• Ohm's Law Relationships:

  • Voltage and Current: Directly proportional.

  • Current and Resistance: Inversely proportional.

• Solving for variables: Use Ohm's Triangle to decide on formula based on which variable is missing.

  • Cover missing variable to identify the appropriate calculation for finding the other parameters.