The Mystery of Voltage

The 1.5V battery. The 9 V battery . Common household items. What is Voltage? What are Volts? After some time investigating, it can be said that I am not clear on the concept.

Lets start with the definitions:

The volt (symbol: V) is the derived unit for electric potential, electric potential difference (voltage), and electromotive force.[1] It is named after the Italian physicist Alessandro Volta (1745–1827).

Also:

One volt is defined as the electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points.[2] Equivalently, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it.

Potential difference and electromotive force. In the second definition, one volt is defined in terms of current and power.

See this link it may be useful. also https://www.youtube.com/watch?v=OGa_b26eK2c

Right off the bat, we have gained some insights that are not usually porduced in the introduction to electronics videos, which define the Volt as "eelctrical Presure" potential, and so on. At one stroke, we have some definitions that will help with, say buiding and amplifier circuit: there is a force involved, well, this si debatable, but also one ampere and one watt hints at the heating and power handling problems we encounter with the humbelr 0.5 W reistor (I have had the pelasure of wathing a resistor burning in a lab) so I knkow it is really real. If we have, say, a 9 V power supply, one ampere will dissipate one watt , which is already over the limit for our little resistor.

Looking at the standard formula for voltage, ie

V= IR

Voltage = Current x Resistance.

I have found it somewhat useful to look at the circuit I am building or any circuit under analysis as the right side of the equations, that is, Current x Resistance, the IR factor. Take a simple circuit suchs as shown below. This set up with a 9V battery (that does not look like a (V battery) can be written as a 9 IR battery: that is, stating the rating of the battery as 9IR. What will this do for us? Well it intantly tells us that the battery is capable of supply 1 Amp across a 9 Ohm resistane. Of course batteries being what they are, will ru down, amps will get less, current will decrease, and so the capacity to supply current will be less.

Measuring Voltage

Things become interesting, even mildly fascinating, when we consider how Voltage is measured. How does a multimeter measure voltage? How does a Voltmeter measure voltage? There is a needle to be sure, card readout, and connect the voltmeter between two points ant he needle will swing, as current passing through the voltmeter wil cause a mange filed whic will exert a force on the coil of the element and then cause it to move, A spring makes it move slower and ore graceful, limiting th movement.

Current has to pass through the boatmen. Not all the current, because theis will bleed the circuit of it current and all of it wll pass thorn the involvement. So we bleed of a small current to measure itn through the voltmenet wna calibare te need Lexington correspnt to and I x R, say 10 K resistot,which will only let a current of I/10,000 pass through, leavin the circuit to let current through it as intended . Most of the current. that is. When this occured tome I immediately asked aphysicst teacher about this and he concurred, yes, that is why we use a Heatsotn brighe or some such circuit ot measure voltae accurate: basically two loops of a circuit where when no current passes through the cirucit then we can be sure accurately wgat te oltage is, (no blleding off current). I cannot remeber what the circuit is, however it hints tat th inaccuracy of involvements meaurements.

This analysis based on current only will help me understand the working og th evoltage divider circuir at the top right. My questions was, if the current at the base is drawn from the current flowung from teh left hadn rsistors then why should one resistor not be enough? Why not rextric the current throgh the base iwht one resistor, the 'bias'resistor? Well then I have actually got a circuit working with only one bias resistor so why doe s this apply to the entore circuit. talking voltage drops does not nake any any snese nhere, how can IR drop when the current is the same thoufht th eciruit.

To chech this out we have to use an acutal curiut iwht two resistors, a battery and a votlementer.