Wednesday, November 20, 2024

How Motors Work

Single loop motor armature. Image author Lookang, CC BY-SA 3.0 via Wikimedia Commons
These are quite good graphics, on the Georgia State University site showing the BIL force on a conductor in a magnetic field, and how a traditional DC motor works. The first practical electric motor dates from 1834.


If I is the current flowing through the armature (the thing that turns in a motor) in amps, B is the magnetic flux density in tesla (how concentrated the magnetic field is) and L is the length of the armature in metres, then the force on the armature coil in newtons is:
 
F =BIL
 
One side of the coil experiences a force F in one direction and the other side a force F in the other direction (because the current flows the other way). These two forces are known as a couple. A couple creates a torque (twisting force) and the magnitude of the torque in newton-metres (units Nm which you'll sometimes see on cordless drill specs) is:
 
T = FW
 
where W is the width of the armature.
The effect of the torque is to turn the armature which is made up of coils wound around a laminated soft iron core, mounted on a shaft.
The motor in the graphic has a single coil. Real world universal motors (which run on AC or DC) in a corded power drill, vacuum cleaner, food mixer etc have an armature with many loops of wire so the electromagnets (the grey things in the graphic) can keep exerting a force as the armature turns. A commutator switches power to the loops via graphite brushes while the armature is turning.
Motors in electric vehicles and cordless tools work on a different principle. They don't use brushes and rely on the interaction between varying magnetic fields in both a stator (a fixed coil located around the internal perimeter of the motor) and a rotor which turns.

What Came Before the Big Bang?

Image created on request by Bing Image Creator.

The general consensus is that space and time began with the Big Bang and everything expanded from a mathematical point. It wasn't as though there was a massive explosion and then everything expanded into a huge, pre-existing void. We couldn't identify a point in space today where the Big Bang occurred and put a plaque at it marking the event. In a sense it occurred everywhere. Before the Big Bang, there was no space, it was created, as was time. So there was also no "before" the Big Bang.
"Nothing was around before the Big Big(sic) Bang" according to Stephen Hawking in this interview where he discusses the concept of four dimensional "spacetime".


Cartoon created on request by Bing Image Creator. The Grammar Police were involved because BIC can't spell !
 

Wave Interference

The red and green waves sum together to produce the red wave..Image author Wolfgang Christian and Francisco Esquembre CC BY SA4.0 International via Wikimedia Commons


The red wave is the sum of the green sine wave travelling right and the blue sine wave travelling left. When the peaks of the red and blue waves are coincident and they add, the result is constructive interference and when peaks coincides with troughs, they subtract, resulting in destructive interference. The waves can be sound, light, radio waves, waves in the sea, ripples in a pond, gravity etc. Wave interference is responsible for the phenomenon of iridescence (e.g. colours on spilled oil or petrol on a wet road), beat frequencies with sound waves (e.g. two tuning forks giving a tremolo effect and periodic rise and fall in sound level) and contouring of coasts when sea waves combine. Coastal features called tombolos where an island joins to the mainland by a sand bridge (e.g. Howth Head or Palm Beach in Australia, used as the film location for the fictitious Summer Bay in Home and Away) are caused by refraction (a type of interference of sea waves).

On "Can Scientists Save the World?" on BBC One Tonight

Illustration on request by Bing Image Creator

 
In a documentary on BBC One, there was a report about a cleantech company called Synjelion who have developed technology that sucks water and CO₂ out of the air and uses energy sourced from solar panels to power a process that produces jet fuel. It's basically a synthetic version of photosynthesis, except plants make sugar, starch and cellulose, using water, carbon dioxide and sunlight. All the wood that makes up a tree comes from carbon taken out of the atmosphere. Meanwhile we breathe out all the carbon in our food in the form of carbon dioxide.

Science Friday Podcast — Prime Numbers

Image by Bing Image Creator

If you remember back to studying maths at school, you might recall that prime numbers are numbers that only be divided equally by themselves and the number one. So 2, 3, 5, 7 and 11 are primes. 4 isn't because it can be divided by the factors 1, 2 and 4. Prime numbers are important for cryptography and security of data and discovering new ones is challenge. Finding increasingly large primes takes time, even for computers, because a number has to be checked with numbers smaller than it to make sure they don't divide in evenly, making the number non-prime. In this podcast, Ira talks with Jack Murtagh, math writer and columnist for Scientific American, about why prime numbers are so cool, and the quest to find the largest one.

Big Picture Science Podcast — Beyond the Periodic Table

Public domain image via Pixabay.
 

Directly after the Big Bang, there were no elements as we know them today. So no hydrogen, helium, copper, gold, mercury, chlorine or any of the other 94 or so naturally occurring elements. There were just sub-atomic particles such as quarks and electrons. A few millionths of a second after the Big Bang, these aggregated to form protons and neutrons. Hydrogen is the most common element in the universe, simply because there's a greater probability of a single electron and proton coming together to form a hydrogen atom. Other elements are more complex, consisting of various arrangements of protons, neutrons and electrons in their atoms. For instance, the total number of protons and neutrons in a gold atom's nucleus is 197 and there are an additional 118 electrons in its outer shells. It's much less likely for over 300 random particles to come together to make up that arrangement, that's why gold is so relatively rare.
In this episode of Big Picture Science, the team discuss the history of the periodic table and how we're making new elements, some useful and others purely for research purposes (The radioactive isotope Americium 241 is commonly used in smoke alarms, others are used for radiotherapy). Guests include Jennifer Pore – Research Scientist of Heavy Elements at Lawrence Berkeley National Laboratory and Mark Miodownik – professor of materials and society at University College London and the author of “It’s a Gas: The Sublime and Elusive Elements That Expand Our World.”

Woodchip Gasifier Genset

I'd like a small version of one of these for turning my garden waste to electricity. I haven't read the full details, but basically it heats or roasts wood chip to make gas which runs an engine and drives an electrical generator, producing heat as a by-product. Gasification was the process used from the 18th century up until the early 60s for making gas from coal, i.e. coal gas. This was stored in large tanks called gasometers. The process was superseded by gas production from naptha, a waste product of the petroleum industry and eventually in the 80s, we started using cleaner natural gas or methane from natural deposits such as the Kinsale Head gas field.
Gasifier gas driven engines were used in the UK for running cars and buses during WW2 when petrol was in short supply.

Sunday, November 17, 2024

Reverend Nicholas Callan and the Induction Coil

Rev. Nicholas Callan. Public domain image via Wikimedia Commons: https://en.wikipedia.org/wiki/Nicholas_Callan...
Did you know that the induction coil is an Irish invention by Reverend Nicholas Callan (1799 - 1864), a physicist and Catholic priest at Maynooth University?
The device is a type of transformer, commonly used in vehicles in the form of an ignition coil for generating the tens of thousands of volts necessary to create a spark at the plugs. Induction coils with an output of hundreds of thousands of volts were used for early spark-gap transmitters. Connected to a tuned circuit and antenna, they could transmit radio waves at a certain frequency. The tuned circuit is the electrical analog of a bell. A spark discharge "rang" the bell by setting off electrical oscillations.. These transmitters would have been used for intercontinental and ship-to-shore communications in the era of the Titanic.
 

Electromagnetic Induction 

 

Electromagnetic induction is a phenomenon discovered by the English scientist Michael Faraday in 1831. If you move a magnet close to an electrical conductor, e.g. a looped piece of wire, the field of the magnet induces an electric current in the wire. It's the change in magnitude of the magnetic field that creates the current, rather than the fact that the magnet is moving. If the field is constant in magnitude, no current is induced. The magnitude of the voltage that creates the current is proportional to the rate of change of magnetic flux, in other words, the faster the magnetic field changes in size, the greater the voltage.
 

How Do Transformers Work?

 

All transformers and electrical generators work on the principle of electromagnetic induction.
The transformers such as those used in older power adapters and corded electronic equipment have a laminated core, made of a stack of wafer-thin, soft iron sections, insulated from each other. A primary coil wound around the core (hundreds of turns of wire) generates a fluctuating current when connected to an AC mains source. This in turn creates a fluctuating magnetic field and that field then induces an electric current in a secondary winding. A transformer simply increases voltage, or decreases it, like the room sized transformers we have at the sub-station in Kilcullen. The ratio of the number of turns of wire on the primary coil to those on the secondary coil, known as the turns ratio, determines the factor by which the output is increased or decreased. So if the input coil has 1000 turns and the secondary coil has 100 turns, that's a turns ratio of 10 and voltage is reduced by a factor of 10
 
Schematic of a transformer. Image author BillC at the English-language Wikipedia, CC BY-SA 3.0
 

What are Induction Coils?

 

Instead of being fed by AC, an induction coil works on DC. It has a primary coil with hundreds of turns of wire and a secondary with thousands of turns. The coil when energised also acts like an electromagnet. This isn't the case with a standard transformer because the iron core is in the form of a closed loop, with no external field. The DC source, e.g. a battery, is connected to the coil via a spring switch, called an interrupter, that can be opened and closed by the force of the electromagnet (the same mechanism is used on old doorbells). On connection of the supply, with the switch closed, the magnetic field in the core grows until the electromagnet suddenly opens the switch, disconnecting the input. The magnetic field rapidly collapses and it's this rapid collapse and change in field that induces a huge voltage in the secondary, much greater than the turns ratio could produce with an AC source. When current is disconnected by the switch, the force of the electromagnet drops to zero, causing the spring to close the switch again, reconnecting the circuit and the cycle repeats indefinitely, generating high voltage pulses at the rate of hundreds per second.
 
An induction coil. Image courtesy Hannes Grobe, CC BY 3.0 via Wikimedia Commons

 
More information on Rev. Nicholas Callan on the Maynooth University website here:

From the Wikipedia Rabbit Hole Day Trip — Poulaphouca, Surge Tanks and Your Washing Machine

The Blue Ridge Dam and surge tank. Public domain image by Tennessee Valley Authority on Wikimedia Commons.
If you look to the left while crossing north over the River Liffey bridge on the N81 at Poulaphouca, you might have noticed a large tank in the distance on the edge of the gorge. This is a surge tank and its function is to protect the pressure tunnel from hydraulic shock or water hammer when feed to the turbines at the power station is turned off suddenly. Hydraulic shock occurs when water is flowing through a conduit (pipe, tunnel etc) and its flow is suddenly interrupted. The sudden deceleration causes a rise in pressure which can cause damage to pipes. Have you ever noticed the sudden thump as water turns off when your washing machine's intake valve closes once the drum is filled? This is also a water hammer effect. However by comparison, the pressure tunnel to the power station is over 400 m long and 4.8 m diameter. That's a huge volume of water in motion with lots of momentum and kinetic energy and when it stops suddenly, that energy has to go somewhere. A surge tank at the power station allows water to flow freely up into the tank, converting kinetic energy into potential energy, rather than as a damaging shock wave propagating back up the pressure tunnel to the dam.