Friday, October 24, 2008

Todays test.....

Giving this to my class this morning:

1) What is electricity?

2) Name three measurements of electricity and define them.

3) Name two types of current and define them.

4) Name two types of circuits and define them.

This test should take about five minutes to complete, if they have studied their class notes and paid attention. It's not 'electron theory' level, but is the basic practical foundations to electrical testing and diagnosis.

They must have this to work in the business.

Answers to follow in comments, when I have time. Take a shot at it if you wish! William the Coroner said...

1. Flow of electrons from an area of greater potential to ground

2. Ohm's Law strikes again. I=V/R where V = voltage, R is resistance to electron flow measured in ohms and I is current in amperes

3. Alternating current which flips polarity back and forth so many times a second, and direct current which doesn't

4. A short circuit that doesn't go do anything and a working circuit where the electron flow goes across a light or whatnot, some resistor that does work.

aepilot_jim said...

I'm taking a stab here. I don't have the benefit of class notes and my last physics class was ahem/years/ahem ago.

1)Electricity is the flow of energy from one point to another. That's an oversimplification of the term.

2)Voltage, Amperage, and Resistance. As for proper definitions. I usually remember them by the garden hose analogy. If a circuit is a garden hose and electricy is the water. Voltage is the amount of water, amperage is the speed of the water and resistance is the size of the hose.

3)Alternating Current (AC) and Direct Current (DC), but I can't think of a good definition of them other than to restate the names.

4)Parallel and Series. I can see the circuit diagrams but I'm having a problem of describing them. One will result in 12V say from 2 6V power sources and the other will only give 6V from the same 2 6V power sources.

How'd I do? From off the top of my head.

Crucis said...

1. Electricity is the movement of electrons through a conductive medium.
2. Amps = the "pressure" of flowing electricity.
Volts = the amount of electricity that is flowing.
Ohms = the resistance to flowing electricity.
3. Direct and Alternating. Direct current flows constantly in one direction as electricity from a battery. Alternating current reverses its flow on a regular basis, such as that found in the home or created from a generator.
4. Series and Parallel. Series circuits have all components connected one end to another. Parallel circuits have all components side-by-side with each end having a common connection point.

That took me a little longer than five minutes. Haven't thought about this for several decades.

dfreed said...

1.
Electricity if the transfer of electrons (I think it may actually be protons) through a conductive medium with the goal of moving energy from one place to another.

2. Volts, watts, and Ohms. Also you may be looking for voltage, resistance and current.

3. Alternating Current, and Direct Current. Alternating current is a form of current where the peak voltage moves from a neutral point, to a peak positive value, back through a neutral point, to a peak negative value, and then return to the neutral value again.
Direct Current it the continues application of a specific voltage at a non changing and non varying value. A/C is more efficient for long distance transmission, with the caveat that long distance transmission is never really all that efficient unless using a super conductor.

4. I am not sure of the context of this question but here are two potentially correct guesses:
A. You can have integrated circuits, where the circuit is contained within a chip, or a discrete circuit where they chips are unique and visible on a breadboard or base medium.
B. An open circuit where current is not flowing through it, and a closed circuit, where power is flowing.

Shrugged says: said...

You folks are pretty good... (g)

I was looking for simple answers from the students. Ones that mirrored what the lessons covered, but with room for 'creative expression' if needed, such as... draw me a diagram that explains the answer.

1) What is electricity? In it's simplist format: The flow of electrons through a conductor. (I teach it this way because it makes understand the generation of electricity so easy to understand).

2) Name three measurements of electricity and define them: Voltage, electrical pressure, measured with a voltmeter in volts.
Amperage, electrical flow rate, measured in amps with an ammeter.
Resistance, the inhibiting of electrical flow, measured in Ohms with an Ohnmeter.

3) Name two types of current and define them: Direct current, where the electrons move in one direction of flow, and alternating current, where the electrons move back and forth with reversing polarity.

4) Name two types of circuits and define them: Series circuit, which has only one path to ground. Parallel circuit, which has multiple paths to ground. (I accept series-parallel as well).

As you can see, we are dealing with REAL basic stuff at this point. We won't touch on voltage drop testing and amperage testing till next week.

The boys flubbed this test, BAD. We gave them the weekend to study, then they will retest. It counts as a 100 point test, each question worth 25 points. All or nothing for each question.

If they blow it again, we restart the whole section and reteach every blessed lesson.

They are cruising through the actual hands on portion, making tests well and coming up with good numbers. Even so, understanding the what/why/how is so important to their career we'll keep pushing till we hit diminishing returns.

Brigid said...

What IS electricity?

The first usage of the English word electricity is ascribed to Sir Thomas Browne in his 1646 work, Pseudodoxia Epidemica:

"Again, The concretion of Ice will not endure a dry attrition without liquation; for if it be rubbed long with a cloth, it melteth. But Crystal will calefie unto electricity; that is, a power to attract strawes and light bodies, and convert the needle freely placed"
—Pseudodoxia Epidemica, 1st edition, p. 51

In this context, an "Electrick" or "Electrick body" was a non-conductor, or an object capable of attracting "light bodies" (like bits of paper) when excited by friction; a piece of amber is "an Electrick", while a piece of iron is not. "Electricity", then, was simply the property of behaving like an electric, in the same way that "elasticity" is the property of behaving like an elastic. ("Electric" continued to be used as a noun until at least 1913.)

It was not until later that the definition shifted to refer to the cause of the attraction instead of the property of being attractive - the physical phenomenon associated with stationary or moving electrons and proton

(2) Elementary my dear Ohmes!

Ohm's law holds for linear circuits where the current and voltage are steady (DC), and for instantaneous voltage and current in linear circuits with no reactive elements. When the current and voltage are varying, effects other than resistance may be at work; these effects are principally those of inductance and capacitance. When such reactive elements, or transmission lines, are involved in a circuit, the relationship between voltage and current becomes the solution to a differential equation.

Equations for time-invariant AC circuits take the same form as Ohm's law, however, if the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials.

In this approach, a voltage or current waveform takes the form Aest, where t is time, s is a complex parameter, and A is a complex scalar. In any linear time-invariant system, all of the currents and voltages can be expressed with the same s parameter as the input to the system, allowing the time-varying complex exponential term to be canceled out and the system described algebraically in terms of the complex scalars in the current and voltage waveforms.

The complex generalization of resistance is impedance, usually denoted Z; it can be shown that for an inductor,

Z = sL\,

and for a capacitor,

Z = \frac{1}{sC}

We can now write,

\mathbf{V} = \mathbf{I} \cdot \mathbf{Z}

where V and I are the complex scalars in the voltage and current respectively and Z is the complex impedance.

Simple right?

(3) First is AC. Alternating current is an electric current whose direction reverses cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves.

Used generically, AC refers to the form in which electricity is delivered to businesses and residences. However, audio and radio signals carried on electrical wires are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.

The second is DC. Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through semiconductors, insulators, or even through a vacuum as in electron or ion beams. In direct current, the electric charges flow in a constant direction, distinguishing it from alternating current (AC). A term formerly used for direct current was Galvanic current.

(4) If two or more circuit components are connected end to end like a daisy chain, it is said they are connected in series. A series circuit provides a single path for electric current through all of its components.

If two or more circuit components are connected like the rungs of a ladder it is said they are connected in parallel. A parallel circuit provides separate paths for current through each of its components. A parallel circuit provides the same voltage across all its components. An old term for devices connected in parallel is multiple, such as a multiple connection for arc lamps.

My brain is tired - time for a beer.

Shrugged says: said...

Lol..... I'm tempted to hit them with that on a quiz, Brigid.... William the Coroner said...

Brigid is a show-off