Electric Circuits and Current Notes

Definition of Electronic Boards:
- All images depict electronic boards.
- These are complex electrical circuits designed to function within electronic devices.
- The first electronic board was patented in 1903.
- Printing wires (conductive paths for electric charges) was developed approximately ten years later.
- Today, flexible circuits can be printed as well.

Analogy of Liquid Levels:
- Imagine two containers with a liquid at different levels connected by a pipe.
- The height difference creates liquid flow through the pipe (analogous to electric current).
- As the liquid flows, it tries to level itself, which stops the flow—similar to how electrical current diminishes without sustained voltage input.
- Pump Analogy:
- To maintain flow, a pump raises liquid from the lower to the higher container, analogous to a voltage generator in an electrical circuit.

Potential Difference:
- A difference in electric potential across a conductor generates electric current, similar to the liquid analogy.
- In a metal wire, mobile electrons (conduction electrons) move from lower to higher potential, opposite to the electric field direction, while positive charges move with the field direction in other types of conductors.
- Inside conductors, an electric field E is oriented from the positive to the negative potential:
- Electric current flows from negative to positive across this field.
Maintaining Current:
- The flow of charges tends to neutralize the voltage difference, leading to the need for a generator to sustain the current flow.
- A circuit consists of conductors connected to at least one voltage generator. If unbroken, it allows current flow (closed circuit).
- If broken, there is no current (open circuit).
- A constant voltage generator maintains a steady potential difference over time.

Conventional Current Direction:
- Defined as the direction of positive charge movement.
- In metals, where mobile charge carriers are negative electrons, if electrons flow left to right, current is defined as moving from right to left.
- It’s conceptually acceptable to switch negativity to positively describe currents without contradiction.

Intensity of Current:
- For a conductor with mobile charges of both signs:
- Charge flows occur in both directions, contributing to a net current.
- The total charge $ext{ΔQ}$ that crosses a given point in time $ext{Δt}$ is given by:
  $Q = Q^+ + |Q^-|$
- Current intensity (I) is defined as:
  I = rac{Q}{Δt}
Units of Current:
- Current intensity measured in amperes (A) is fundamental in the SI system.
- 1 A signifies 1 Coulomb (C) of charge flowing per second.

First Law of Ohm:
- Expresses the relationship between voltage difference (V), current intensity (I), and resistance (R):
  I = rac{V}{R}
- The unit of resistance is ohms (Ω) (Volt/Ampere).
- Experimental data can show how current intensity changes with varying voltage differences using an ammeter (in series) and a voltmeter (in parallel).

Series Connection:
- Total resistance $R{eq}$ in series is the sum of individual resistances: $R{eq} = R1 + R2 + … + R_N$
- Adding resistors in series increases total resistance.
Parallel Connection:
- The total resistance $R{eq}$ in parallel is given by: rac{1}{R{eq}} = rac{1}{R1} + rac{1}{R2} + … + rac{1}{R_N}
- More branches (resistors) in parallel decrease total resistance.

First Law (Nodal Law):
- The sum of currents entering a node equals the sum of currents leaving it.
Second Law (Mesh Law):
- The sum of the electromotive forces (emf) and the potential differences in a mesh equals zero.

Energy Transformation:
- Current through a resistor converts electrical energy to thermal energy (Joule Effect).
- Example: In incandescent bulbs, energy is mostly dissipated as heat instead of light.

Ideal Generators:
- Maintain a constant emf independent of current.
Real Generators:
- Have internal resistance affecting voltage output when current flows.
- The emf can be measured using an electrometer under no load conditions.