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The Solder and Circuits web site is set up for young people who have some knowledge of electricity.
Forrest Mims is an author who has written many introductory electronics books. Getting Started in Electronics is available at some Radio Shacks.
For those who need to catch up on knowledge, this web page is provided. Some of this knowledge requires research or coaching.
Do you know that magnets have a north pole and a south pole? Do you know that there are insulators and conductors, the latter being mainly metals? Batteries have plus and minus, usually color coded as red and black. This is obvious on car batteries.
The schematic above has a ground wire along the bottom.
Though ground is not marked by this symbol in the schematic, most schematics do show ground with this symbol. It is called ground because, in 120VAC-powered circuits, the power-plug's round prong does connect to a four-foot-long ground stake near the power entrance of the building.
With battery-powered circuits, there is no ground connection when you aren't charging the battery. Even so, the circuit is said to have a ground, and it is normally the negative end of the battery. Audio systems, like PA systems, have a ground--it is the copper-braid shielding of the cables, and the metal shells of the cable connectors. Desktop computers have a ground, the metal case. A car has a ground: the engine block, the chassis or body, and the negative end of the battery.
Ground is zero volts for the circuit. The power supply for the circuit, which might be a battery, provides + voltage. Sometimes, there is also a negative ( - ) supply for the circuit. When you measure the supplies with a meter, you connect the black meter probe to ground.
Resistance is like a 1000-ohm resistor. Resistors are the most common, cheapest parts in circuits, as cheap as half a cent.
Resistance is also in wires, and it makes wires heat up when there is a lot of current. A thin extension cord should not be used with a vacuum cleaner, the copper has too much resistance that makes the cord get warm or hot. A thick extension cord is needed for a vacuum, toaster, hair dryer, or any high-current device.
Talking about getting warm, watts is heat. Watts are a measure of power. Watts = amps * volts, very simple. A hair dryer that uses 9 amps is using 9 * 120 = 1080 watts.
A 60-watt lamp uses .5 amp. 60 = 120 * .5
60 watts in anything gives a high temperature. For little resistors in electronic devices, .5W is pretty high and gets the resistor too hot to touch. Normally, the resistors, transistors, and integrated circuits use .1W or less. Battery-powered devices have to have low-power, cool parts, otherwise you are going to have to recharge too often. A cell phone usually is cool during a call. But if you are distant from a cell site, the phone has to switch to high-power mode, and it may warm up in your hand in ten minutes.
Resistance, volts, and amps are related by the simple Ohm's Law: V=IR I=V/R R=V/I where I is the amps
Example: in an 8 ohm speaker, if volts is 3.5, current = V/R = 3.5/8 = .44 amps. P=IV=.44*3.5=1.54 watts If the speaker is 5" or less, this might burn it out.
The voice coil in a speaker can get hot if you play loud music.
The big amplifier that you might connect to this speaker can put out five to fifteen amps, and that gets the copper wire in the voice coil hot. (The voice coil makes an electromagnet. It pushes and pulls on the permanent magnet. That moves the speaker cone up and down to make sound waves.)
A big amplifier follows.
A little amplifier follows.
The Gibson guitar amplifier takes a small voltage, like .2 volt, and amplifies it to 2V or 20V or whatever you need.
Amplification is very widespread. Any microphone is producing only a tiny voltage, like .0001 volts, so an amplifier is needed to boost that up to .2V or 2V or 20V.
The amplification to produce 2V from .0001V is the division: 2/.0001=20,000.
Radio waves, like in cell phones, radio, or broadcast or satellite TV, are typically amplified by 500,000. Radio waves in cable TV are typically amplified by 50,000.
A challenge in an amplifier is that when the amplification is over 50, there are reasons that the amplifier might self-oscillate. This happens with PA systems when there is feedback, when a speaker puts too much volume into one of the microphones. The system squeals, loudly. One of the pursuits in amplifiers is to build amplifiers that don't self-oscillate due to "layout" and "lack of decoupling capacitors" within the amplifier. This can only be learned by building amplifiers, experiencing oscillation, and doing cookbook things to stop the oscillation.
Voltages are measured in volts, millivolts, and microvolts. The symbols are V, mV, and uV. In uV, the u is a stand-in for the Greek mu. If your computer font can show mu, that is preferred over u.
The sound waves from a speaker or your vocal cords are, in the simplest case, sine waves.
Here is a sine wave and also a square wave and triangle wave.
Following are musical and dissonant waves.
The sine wave (the top wave above) is the only wave that has no harmonics. Pure sines have no corners. The mathematical "slope" of a sine is a sine with 90 degrees phase shift. Vibrating strings produce sine waves once the pluck damps out. A mass suspended on a spring bounces up and down with sine motion.
If harmonics are added that are twice, three times, or more the fundamental's frequency, it sounds normal. But the addition of a sine that is not an integer multiple of the fundamental's frequency produces a nonrepeating wave that does not sound good.
The sine, the top wave, has a "period" of 12.5 seconds. The frequency = inverse of the period.
Audible waves are 20 Hz to about 10,000 Hz. (Hz means cycles per second.) People's voices are about 300 Hz to 3000 Hz.
In amplifiers that don't need DC coupling, AC coupling is accomplished through capacitors. Even though a capacitor has an insulation layer between the metal "plates," AC waves can pass right through.
Considering that graphs are important to electronics, here are some graphs that can be talked through.
In what month was sales at a peak?
In the graphs above and below, is it a function of time?
Is this a graph of a function of time?
In the graph above, what does the blue curve show? How about the red curve?
What is the speed of the car at A? What changes at B?
If C shows a stop at a traffic light, what is the peak speed between the two traffic-light stops?
At D, what is the peak speed?
The D and E situation shows 45 m.p.h. in a 30 zone. The driver is pulled over by a policeman for a speeding ticket. How long does it take for the driver to get back on the road?
From the time the driver enters the town until the 42-minute point, does the car travel very far?
At G, the car is passing through an industrial area. What does the speed limit seem to be?
Once the car is past the town, what is the speed (at I)?
Why is the slope at H different from the slope at J?
Why is the slope at F flat?
Electric & Magnetic Demo Items Available for Presentations
Electric & Magnetic Demo Items Available for Presentations
Speaker
permanent magnet & electromagnet pull and push the cone
the lighter-mass magnet is built onto the cone, it is the electromagnet coil
demo with speaker onto battery
Solenoid electromagnet produces linear motion
DC Motors are in all moving toys plus hair dryer Dremel Tool is also usable with AC graphite brushes
Induction Motor
rotating magnetic flux pulls a conductor with it, in a circle
"slip," the rotor spins about 90% of the RPM of the rotating magnetic field of the stator. The rotating field is from double windings, one of which is high resistance or fed from a cap to get a phase shift
no graphite brushes
Nikolai Tesla invented this
demo hard-drive magnet with aluminum strip as an analogy to induction motor
Stepper Motor microprocessor-controlled electromagnets pull armature at variable speed no "slip" two or more phases
steel laminations in motors and transformers to prevent "shorted secondary" effect
magnetic flux around even a straight wire inductance L is about 10nH per inch
flux when you have a loop of current
flux when you have a helix, inductance in Henries is proportional to turns squared,
L μH = .8 r2 turns2 / (6 r + 9 length + 10 b) using inches
Flux doesn't want to be bunched together.
Flux through a helix tries to expand an oval cross section into a circle--
consequence for MRI magnets & particle-accelerator magnets.
Lightning current tries to straighten out any kinks or turns in a wire, to the extent of rupturing the wire
ferrite EE cores
Flux outside a toroid cancels, over a diameter or two away from the toroid. Consequence: 1) external AC flux doesn't generate an interference voltage in the toroid, if the flux is uniform 2) toroid does not radiate radio waves like a helix does
Flux with two electromagnets, check with compass
Rolled capacitors make your own cap, measure it
Capacitor blocks DC, passes AC (listen to this with speaker)
22,000 μF time constant with 8 Ω speaker + 20 Ω is visible time constant,
RC = 28*.022 = .62 second Excel graph of the equation as f(time)
Inductor passes DC, blocks AC. Inductors for high voltage like an auto induction coil.
The first electric component was capacitor: Leyden jar, charged from static machine like Wimshurst generator or sulfur ball
Voltage measured by anatomical effect, applied to tongue or between ears
Energy storage in inductors & capacitors. Energy storage caps for physics experiments. http://www.amstechnologies.com/products/power-technologies/high-voltage-components/capacitors/pulse-discharge-capacitors/view/capacitors-series-c-high-energy/ particle physics, pulsed laser, seismic power supply, defibrilator, flash lamp, lithotripsy E=.5 C V2 E=.5 L I2 just like E=.5 m v2
200V aluminum electrolytic cap discharged with a spark, calculate Joules
charged cap plates attract each other--creepy demo with foil and waxed paper
Pull charged cap plates apart: increases voltage! because you are pushing against a force, and building up stored energy because C in farads = charge/voltage and charge is the same but C is going down, charge is merely the number of electrons, one coulomb = 6.24x1018 electrons = 1 amp for 1 second
E field in a solar cell separates electron and hole when a photon pushes a covalent electron into the conduction band. The electron and hole show up at the outside metalization of the solar cell to be used as electric power. (E field is from the P and N donor atoms frozen into the silicon.)
E field in a JFET or MOSFET or vacuum tube is how drain or plate current is controlled, to make an amplifier.
Zero E field inside a closed, metal box except when there is a dipole in the box
the same voltage all along a copper wire, except for small voltage like
.0005V caused by current, V=current * ohms
lightning current goes over the outside of a metal car or airplane, does not get inside
radio-transmitter current electrocuting a person burns skin & outer muscles
cell-phone energy does not penetrate far into the brain
microwave oven heating is on the skin of food; no current 1/4" inside
the food; hard to bake a potato
Birds can land on high-voltage wires (15,000 V) because the field is not
too different across 1/2 foot
Line workers in Communist China during Great Cultural Revolution did
bare-hand work on 220V wires because Chairman Mao gave them strength
Eagle flying between phase wires at 150,000 V--if there is an arc,
the eagle becomes a ball of fire
Squirrel bridging 7500V to ground dies from internal steam explosion
Electric transmission-line workers can climb on live 250,000V wires and work at the ends of the glass insulators if they wear chain-mail suits--no field inside a box. But they must be careful to not bridge to ground or another phase--would be a short circuit. Live-line working on Wikipedia, "live line work helicopter" search on Yahoo.com.
No AC H field inside a closed, metal box except when there is an AC electromagnet inside--currents are induced in the inside wall of a box to cancel any AC H field coming from an internal AC electromagnet
No DC H field inside a high-permeability box
A copper band outside a 60Hz or 70kHz transformer reduces H field escaping the transformer
An antenna is when a conductor carrying an AC current is at least wavelength/8. Current becomes weaker along the wire as energy escapes. The conductor doesn't need to be a wire, it can be any shape including metal covers that you would expect to be a shield against radiation.
Radar field of a radar antenna instantly creates cataracts in eyes of a person getting in the beam--lens of eye has so little blood flow that there is no fluid cooling of the lens
Radar field of DEW-Line ICBM radars, 1957, was so intense that a frozen turkey suspended at the focus would burst into flame
Radio-frequency fields can't penetrate metal sheet, not even foil, but can penetrate a seam between metal plates--PCs must have metal cases to satisfy FCC, and seams need bare-metal grounding points
Skin effect affects even high-current 60Hz wires, there is a limit to the diameter of 60Hz wires
A high-pay, electrical-engineering career: consultant mitigating excessive RF signals coming from products that are close to being manufactured
Intense laser light can ionize air molecules (makes ozone), when E field exceeds 83V per .001"
Electric transmission lines over 150,000V are split into 2 or 4 parallel conductors with 9" spacing,to lower the E field at the surface of the wire, to not ionize the air
Farmers whose tractor eqpt contacts drooping electric transmission wires--voltage arcs across tires & blows them out, but farmer jumping off tractor is pulled back by E field 8^ (
Resistors have resistance on purpose
R = V / I
the most common electrical part, commonly 3 Ω to 10,000,000 Ω
given a voltage and desiring a current, find R = V/I
hair dryer, electric stove, strip heaters in a home furnace, incandescent lamp, iron,
popcorn popper, electric blanket use nichrome wire (lamp is tungsten)
wire resistance is why motors heat up search for AWG wire gauge
P = V * I, commonly up to 1500 watts but .1 W in an electronic circuit
Speakers 4 Ω and 8 Ω, P = V2 / R like 202 / 8 = 50 W
Radio waves have E field and H field and experience a resistance of 377 Ω through the air, though they don't lose energy. Coax cable has 50 or 90 Ω, twisted pair is 100 Ω.
Voltage is like water pressure, current is like gallons per minute.
Does a battery held in your hand have voltage? Is current flowing?
Series loads on a battery: add up the voltages
Parallel loads on a battery: branch currents add up to battery current
DC is easy enough because batteries are all around. But DC won't work with transformers; transformers must have AC.
Shock possible above 20V; current through chest over .003 amp is dangerous.
LED onto a battery: limit the current with 1000 Ω or so, use at least 3V battery
https://sites.google.com/site/solderandcircuits/home/progress-using-switches-and-lamps
Props: battery, compass, DMM, tape, 120VAC multiplier ckt, parts samples, solar cell fragments, iron filings, flyback transformer, sample surface-mount parts, amplifier schematic
file Electric and Magnetic Demos on IRON computer.odt
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