Clarification: the role of resistance in producing heat / light (e.g. incandescent lightbulb)

I'm reading Code: The Hidden Language of Computer Software to get a better understanding of what makes a computer work. Early on there is some elementary explanation of what electricity is, and how we measure it. The book then goes on to say that, consider an unconnected 1.5v battery, air is a poor conductor, and so the flow of electrons / current is unobservably low as I = V(1.5) / R(extremely high). When the circuit is fully connected, the resistance drops, and amps increases. The book then goes on to explain that if you have a very high voltage (>>1.5V) with relation to a very small resistance, eventually the increasing current will heat up the wire, make it glow, and perhaps even melt it.

The book then goes on to incandescent light bulbs, explaining how a tungsten filament is heated until it glows. But in this explanation it cites the reason for this is due to the high resistance of the filament (makes sense, its thin and very long).

My confusion comes with these two conflicting statements from the book: 1 - A low resistance and high enough voltage will produce enough heat for the wire to glow. 2 - A high resistance will produce enough heat for the wire to glow.

I THINK I understand - that heat is produced by the accumulation of large numbers of electrons in the same spot. Therefore, with an extremely high current (high voltage, low resistance), many electrons flowing at the same time = many electrons in the same spot = heat and light. Likewise, higher resistance = slowed current = many electrons in the same spot = heat and light.

While I understand this is a very elemental question, I would appreciate any clarification. Searching online has not given an explanation in terms that I can fully accept.

• You probably need to find a better book or online explanation. It is not very helpful to think of voltage and resistance as low or high. Voltage = current X resistance or current = voltage / resistance. Incandescent bulbs are available for 3 volts as in a flashlight or 12, 24, 120, 240, up to 277 volts or perhaps higher. They have whatever resistance is necessary for the desired power with the available voltage. Power = voltage squared divided by resistance. Electrons don't accumulate to produce power, they flow through resistance. It is somewhat like friction.
– user80875
Oct 7, 2021 at 1:55

Frame challenge - you don't need to understand electricity at all to understand computing.

After all, computers are built on top of a logic implementation, and you can build logic using electricity, or pneumatics, or hydraulics, or even shifting rocks.

You need to understand electricity to understand the implementation of the logic used to build all electrical logic based computers.

As a computer person, you'll know about software stacks, for instance to describe communication. Applications on the top level draw on resources from lower layers, and the stack eventually ends up at the physical layer at the bottom. When programming or debugging this, you wouldn't dream of dealing with more than a couple of adjacent levels at the same time.

Most electrical engineers don't even bother to understand down as far as electrons, as unless you do them right, simple 'explanations' involving them get you into all sorts of trouble.

• Thanks for your response. I see, so typically, as with i.e. software development, high level languages etc., it is common to look some layers of abstraction above the fundamental levels of electrons?
– user297363
Oct 7, 2021 at 6:29
• I have seen and operated a computer that was a row of giant handles interlocked with a "locking bed" of sliding bars and notches. Some handles threw very easily because they only moved bars in the locking bed, or turned on a railroad signal light. Others operated long push/pull linkages that left the building and moved railroad turnouts 200m away. That's why the handles are so big. Oct 7, 2021 at 7:03
• @Pbro98 Yes. If you're building a PC, then connecting a SATA cable might as well be a hydraulic hose, for all you know. Building PCBs from chips, you'd need to know logic, circuit theory, and wave theory, but not electrons. Building chips from standard libraries, you'd only need boolean logic. Designing the devices that make up the libraries, and the semiconductor materials that underpin the chips, then you'd start to worry about electrons and holes, but at the quantum mechanical level, not Drude-model billiard-balls heating incandescent filaments. Oct 7, 2021 at 8:01
• @Harper-ReinstateMonica ... and was this machine Turing complete? Oct 7, 2021 at 8:02
• @Neil_UK not that one alone, but it was connected electrically to others. Thank God they didn't develop sentience! Oct 7, 2021 at 16:05

No, electrons don't really accumulate the way you imagine - what's really happening is that energy is being converted into heat, which is converted into temperature rise.

Energy is an abstract idea that has to do with any kind of change in a closed System. So we have to consider Energy as being the cost of changing the system from one configuration (or "State") to another state.

Power is the rate at which Energy is delivered.

Energy is the (multiplicative) product of Voltage and Current.

Current is the flow rate of units of charge ("electrons" but not really), and Voltage is how much energy each unit of charge is carrying.

So if there is lots of Voltage but no Current, there is no Power and no Energy is being delivered. And if there is Current but little or no Voltage, there is no Power and no Energy is being delivered.

Heat is Energy that is being put into a system or drawn from a system. And materials have some thermal properties, Heat Capacity, which converts that Heat into changes in Temperature (which is what non-engineering people would call "Hot" or "Cold").

So a resistor is made of a kind of material that has some electrical properties that relate to electrical Current and Voltage, and some thermal properties that relate the Power (= Voltage x Current) to a rise in Temperature.

Electrons really aren't a good way to understand electricity, the way electrons behave is very counter-intuitive and leads to all kinds of misunderstandings.

William J. Beatty has published some nice introductory materials on this subject, http://amasci.com/ele-edu.html that go into some detail about how electricity really works and the various blind alleys that often trap students.

• Thank you for your explanation and those resources, I had a feeling that the oversimplification of the topic might be the cause of confusion / uncertainty. To what level do you think I need to understand the properties of electricity to understand computing systems? Typically I only really see it discussed in the context of binary signals (open / closed). Are there any other higher level concepts you think might be of use to gain a fuller understanding?
– user297363
Oct 7, 2021 at 3:19
• @Pbro98 To understand computing? Not at all. There's no need for a computer to be electronic in the first place--you can make computers that are all hydraulic or even mechanical. Oct 7, 2021 at 14:56
• Thank you, so in terms of the original question (at risk of oversimplifying), ignoring the idea of electrons. As resistance (e.g. of our filament) goes up, we need more power (i think?), we lose some power as heat + light through this filament. Conversely, if our wire carrying the electricity to the filament has a resistance which is too low, or we provide a voltage far too high for the job at hand, the current is so large that we end up dissipating power as heat through our wire. So its about considering the correct balance between voltage and resistance for the job at hand?
– user297363
Oct 8, 2021 at 18:40

You are really not on the right track with this business about electrons being in the same place. The filament has resistance of R. You seem to get that. Resistors convert energy to heat. The equation is as follows:

P = V^2 / R

Where P is power in Watts, V is voltage, and R is the resistance of the filament. It should be noted that the resistance, R, goes up substantially as the filament heats up.

Watts can also be called Joules per second. Joules are energy. Some of that energy heats up the filament, and some escapes as radiation. Once the filament is hot, there is also convection and conduction heat loss from the hot filament.

Don't think about electrons for now. Electrons are transported by the filament, but the number of electrons in the filament doesn't change appreciably over time. Some enter one side and an equivalent number exit the other side of the filament.

• In particular it is important to note that for a given voltage, dissipated power goes up if the resistance is decreased. If the resistance is too small however, the current will be so large that a significant power is wasted in the wires connecting the battery to the bulb, and in the battery iteself. Oct 7, 2021 at 6:54