Current Electricity and Ohm's Law

Current Electricity

• Current electricity is the flow of electric charge.
• Electric current (I) is the rate of flow of electric charge. It's measured in amperes (A), where 1 ampere is 1 coulomb per second (1 A = 1 C/s).
• The direction of conventional current is the direction positive charge would flow. This is opposite to the direction of electron flow.
• Current is directly proportional to the voltage and inversely proportional to the resistance (Ohm's Law: I = V/R).
• Voltage (V) is the electric potential difference between two points, measured in volts (V). It's the driving force that pushes the electric current.
• Resistance (R) is the opposition to the flow of electric current, measured in ohms (Ω). It depends on the material, length, cross-sectional area, and temperature.

Ohm's Law

• Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points.
• The constant of proportionality is called the resistance.
• Mathematically, Ohm's Law is expressed as: V = IR
• This relationship is fundamental in circuit analysis.

Electric Circuits

• An electric circuit is a closed path through which electric current can flow.
• Basic components of a circuit include:
  • Voltage source (e.g., battery, generator)
  • Conductors (e.g., wires)
  • Resistors (e.g., light bulbs, heating elements)
  • Switches (to control the flow)
• Circuits can be:
  • Series circuits: components are connected end-to-end in a single path.
  • Parallel circuits: components are connected across each other with multiple paths.

Series Circuits

• Total resistance in a series circuit is the sum of individual resistances. (R_total = R₁ + R₂ + R₃...).
• The current is the same through all components.
• The total voltage is the sum of the voltage drops across each individual resistance in the circuit. (V_total = V₁ + V₂ + V₃...).

Parallel Circuits

• Total resistance in a parallel circuit is calculated using the reciprocal formula: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃...
• The voltage across each component is the same as the source voltage.
• The total current is the sum of the individual currents through each branch.

Conductors and Insulators

• Conductors allow the free movement of electric charge and have low resistance.
• Insulators restrict the movement of electric charge and have high resistance.
• Semiconductors have intermediate resistance values and their resistance can change with temperature or the addition of impurities.

Factors Affecting Resistance

• Material: Different materials have different resistivities, which affect their resistance.
• Length: Longer conductors have higher resistance.
• Cross-sectional area: Wider conductors have lower resistance.
• Temperature: Resistance generally increases with temperature for most materials.

Power in Electric Circuits

• Electrical power (P) is the rate at which energy is consumed or delivered in an electrical circuit. It's measured in watts (W).
• Power is related to voltage and current by the formula: P = IV.
• Power is also related to voltage and resistance by the formula: P = V²/R
• Power is also related to current and resistance by the formula: P = I² R

DC vs AC

• Direct Current (DC): Current flows in one direction. Batteries provide DC power.
• Alternating Current (AC): Current periodically reverses direction. Power grids use AC for efficient transmission.