# Ideal Voltage Source

An **Ideal Voltage Source** has several properties which allow the voltage source to **always **provide the rated voltage **independent **of the circuit **resistance** and **current** drawn.

These properties are:

**Never goes flat****Always**maintains the**same voltage independent of current**- Voltage sources can
**Supply**or**Absorb power (more on this quantity soon)** **Wires**have**zero resistance**- Has
**no internal resistance** - It
**supplies ANY current necessary**to provide its**rated voltage**

**Note: In a** **non-ideal independent voltage source, which has finite internal resistance, the supplied voltage can decrease significantly when the current draw is large (like draining a battery) due to the IR voltage drop across the internal resistance.**

The typical case is shown below:

The voltage source, **Vs**, provides 3.3V which is dropped across the 3.3kΩ resistor and a current of 1mA is flowing through the circuit (which you can check with **Ohm's Law** :))

One of the edge cases is shown below. This is a **short circuit:**

This circuit has the following properties:

**This zeroes the effect of an ideal voltage source****As wires have zero resistance**there is**no voltage drop across the wires**and hence this circuit is**logically impossible (would require the supplied voltage value to change which breaks the definition of an ideal voltage source)****Short Circuit => R = 0Ω**

**Note: In reality, wires have a very small resistance, so to drop 3.3V the current must be very large which will increase collisions in the wire building up heat which would most likely burn out the wire (do not try this at home :) )**

The final edge case is shown below. This is an **open circuit:**

This circuit has the following properties:

- Logically makes sense,
**current is 0A** **As wires have zero resistance, the open point is the difference in electric potential from the terminals**- Can sense charges through air so
**there is still a potential difference** **Open Circuit => R = ∞Ω**

Intuitively you can think of the charges on each terminal spreading across the wires up to the open circuit point so we have **positive charges** on one side, and **negative charges **on the other thinking in terms of conventional current, eventually reaching a point of equilibrium where no more charges move hence we have 3.3V across the open circuit. The dotted boxes around each terminal up to each end of the open circuit indicate that the **same voltage** is observed across each length so we would measure 3.3V at any point on the *positive side* and 0V on the *negative side*. This action is particularly important for another fundamental component known as **capacitors **which we will discuss further later :)