Electrical theory 1.1 - volts, amps, watts

Here I'll explain in simple terms what volts, amps, watts are. This can be confusing to you so I'll give an analogy to help you understand.

Voltage or volts: is the driving force trying to get current to flow. If the circuit is NOT continuous, current can't flow. Voltage only 'exists' in the circuit (called 'energised') - it doesn't do work. (Unit Volts or V)

Current: when the circuit becomes continuous, current will flow (as electrons) in the circuit and it does the work. (Unit Amperes or A)

Analogy:
You want to water your garden with a hose. You turn on the water at the tap and pick up the hose. The nozzle is turned off and no water comes out. However, you can feel the water pressure (from stiffness of hose) and a bulge in the (cheap) hose. See Fig. 1. You could say the hose is energised with water and pressure!

You turn on the nozzle and water sprays out according to the size of opening the nozzle is adjusted to. Also the bulge and hose stiffness disappear. See Fig. 2. You could say the hose has a current of water coming out!

Electrical equivalent:
In your home, you have a mains voltage supply ( from the street transformer), a light switch, and wiring to a light on the ceiling (the 'circuit').

Light switch is OFF: voltage exists up to the switch but since the circuit is not continuous, the light is not lit (not energised), ie no current flow. An electrician could measure the voltage at the supply side of switch to show voltage exists. See Fig. 3.

Light switch is turned ON: the circuit becomes continuous and the voltage forces electrons to flow from transformer, through the light bulb to radiate light, then back to the transformer. This electron flow is called current flow and the light bulb is working! See Fig. 4. Also the light bulb contains an amount of resistance according to its wattage rating.... oops new terms! This resistance determines how much current will flow just like the size of opening in the nozzle (Fig. 2).

Resistance: an apt name for the OPPOSITION to (ie resist or limit ) the voltage's force to make current flow.  (Unit Ohms or Ω )

Wattage: describes how much power is in the circuit, eg a 100W light bulb gives off more light power than a 60W light bulb. (Unit Watts or W)

 

Key points:

 

Voltage = electrical force

Current = flow of electrons which does work

Resistance = opposes the voltage to limit current flow

Wattage = amount of power