# Basic Electricity Lesson 4

After knowing the conductivity of insulator and conductor,  it is time to know about several electronics components.

1. Voltage source – like a battery. Car battery, AA, AAA, C, D batteries are of these. These batteries are not ideal but we can approximate it to be so.

2. Current source – just theoretically made model, but when a transistor is modelled, it is approximately having the current source property.

3. Open circuit or open switch –  terminals is across the insulator and no current is supposed to flow.

4. Closed switch or short circuit – terminals is connected by the conductor and allow any current without much voltage lost or dropped.

5. Resistor – a linear device which follows Ohm’s law, more current is due to more voltage applied. It can be made from conductor which has a higher resistance when it is longer. Mostly made from carbon.

The conductivity characteristics or i-v characteristics can be illustrated below:

Comparing various components using the i-v characteristics, we can tell the voltage source is similar to a short circuit or closed switch when the voltage is decreased to zero. On the other hand, the current source is similar to an open circuit or open switch when the current is reduced to zero. The open switch is equivalent to infinite resistance and the closed switch is equivalent to a zero ohm resistance.  If you do not know ohm’s law, here it is: R=V/I or say resistance is voltage per unit current or ampere. From the i-v characteristic, the slope is I/V which is then called G, the conductance. G is opposite of  R.  Better conductance G means poor resistance R and vice versa.

This is why the horizontal line has a slope of zero means not conducting, thus it is open circuit and the vertical line has a slope of infinity means perfect conductor and no resistance, that is, a short circuit.

These characteristics should be remembered when electronics is being studied.