Here are my notes on Experiment 4. I don't have to have ALL of this memorized do I?
kinda, yeah. Don't worry, the more you understand it, the more these things will become very obvious second nature to you and eventually you'll wonder how you could have possibly misunderstood.
Anyways, here are my notes:
-V = Kilo-Ohms * A
V = Ohms * A, normally expressed as V = IR (I = current in amps, R = resistance in ohms)
It helps to remember an expression "V over (I times R)".
Draw V / (I*R) as a fraction.
it forms a triangle with V on the top, and I and R on the bottom.
If you cover the one you want to calculate with your finger, the formula is revealed.
If you cover V (looking for voltage) you get I * R.
If you cover I (looking for current) you get V/R.
If you cover R (looking for resistance) you get V/I
So remembering this one simple thing can help you with three formulas.
Also it pays to note the difference between the thing you're measuring and the units it is measured in.
So V is voltage, measured in Volts (all V, easy)
I is current, measured in Amps (A)
R is resistance measured in ohms (Ω)
-Higher resistance limits amps/current & blows fuse in meter
Higher resistance means less current for a given voltage -- I = V/R.
But lower current doesn't blow fuses, higher current does. So too low a resistance can blow a fuse.
Your meter on a current range has a very low resistance. So putting that across a voltage will allow a very high current to flow, possibly blowing the fuse.
You normal place the meter in series with a load. This means its low resistance doesn't drop much voltage (V = I*R), and the load continues to operate pretty much like it did without the meter there.
-Can only measure current when it passes through meter
Yes, the current has to pass through the meter to be measured.
-Resistors in series are oriented so one follows the other
This is called placing resistors (or anything else) in series.
You can also place them in parallel, with each resistor placed across the others (like the rungs of a ladder).
When placed in series, the total resistance is the sum of all the resistors.
When placed in parallel the calculation is more complex, but the overall resistance is lower than the lowest value resistor in that group.
-2 equal valued resistors in series doubles Ohms b/c electricity has to pass through 2 barriers in a row
Yeah, that's a good way to think about it
-Resistors in parallel divides total Ohms b/c electrons can take 2 paths instead of 1
Also a good way of thinking about it.
-resistors are not usually put in parallel but a lot of other components are put in parallel
This isn't a rule. Depending on what you're doing you choose the right approach.
The important thing is being able to spot series and parallel, and understand how to wire things up that way.
-Amps are originally measured by the letter "I" or inductance, which is the ability to induce magnetic effects
Here is where it gets a bit tricky.
I (current) is measured in Amps (A).
A device called an inductor (often shown as I on a schematic) has a value of inductance measured in Henrys (H).
Magnetism is getting more complex. You have to start thinking about things called flux density, and reluctance, and other quite weird things.
However, if you have a current you have a magnetic field, and if you wind a wire carrying a current into a coil you make that magnetic field stronger. Placing an iron core in that coil increases it even further. All of these have a relationship to inductance, but if I were you, I'd leave my understanding pretty basic on inductors and magnetic effects right now.
-Volts are difference in voltage b/t 2 pts in the circuit
Almost *exactly* right. Volts are the unit we use to measure potential difference. We normally just call it voltage. And yes, it can only be measured between 2 points (remember that current is measured *AT* a point).
As a consequence, you can see that voltage measurements are always made by placing the meter in parallel with the device.
-I or Amps = current flowing between 2 pts
That may be true, but it is more accurate to say that it is the current flowing past a point. If we have a long wire passing a particular current, you only need to measure it at one point. As long as there are no other connections to the wire, the current will be the same at each point along it.
-R or Ohms are the resistance between two points
Resistance (abbreviated R, using R on a schematic, and occasionally shown as R instead of Ω) IS the resistance between 2 points.
-Ohms law is useful for determining how much resistance, amps, etc to put into a circuit, while still getting the max results
Ohms law tells you the relationship between voltage and current for some device having a linear resistance R. Not all resistances are linear. globes and LEDs are non-linear resistances. You can't say they have a certain resistance unless you specify more conditions.
-ohms law:
V = I * R
I = V / R
R = V / I
Yep. and that;s the big one to remember as I pointed out above.
-Watts are the amount of work the electrons are doing
Yep, that's pretty good.
There is a subtle difference between "work they are doing", and "work they have done".
"work they are doing" (or "work that is being done") involves time, it is a rate at which it is happening. Watts are exactly this. They tell you how much work is being done every second. This is called Power.
"work they have done" (or "work that has been done") is a total amount of work, it doesn't involve time because you don't care if it was done in a second, 3 seconds, a week or a year. This is actually called Work, and is measured in Joules.
Interestingly, a unit of power is "horsepower" which describes how much work a single (presumably standard) horse can do in a second.
Also interesting is that if you go into Macdonalds, you may notice they tell you how many kilojoules there are in a burger (They do this in my country, maybe not yours, but you'll find it on many food labels too). That is a measure of how much energy you can get from that food.
-large batteries have low internal resistance
Generally peaking that is correct.
The only time it's not is in odd cases such as batteries with a huge number of very small cells, or if you make a battery from coins and wet paper.
If it's a normal battery, then this is a good rule of thumb.
yep, you said that
- Lithium batteries are low internal resistance also
Yes, in addition to size being important, the type of battery makes a large difference too.
lead acid batteries have a very low internal resistance. Carbon-zinc batteries have a much higher resistance. But if the type of battery (normally called the "chemistry" of the battery) is the same, and the number of cells is the same, then in almost 99.9% of cases the internal resistance will fall as the battery gets larger.
yep. a kilo-anything is 1000 of that thing.
Unusually for a multiplier larger than 1 (k = 1000), kilo uses a lowercase k.
-Mega-Watt = 1000,000 watts
Yep. And a Mega anything is a million of that thing.
This is the normal case. M (1,000,000) is greater than 1, so uppercase.
milli (m) is < 1 (it's 1/1000). So don't get m and M mixed up. Also notice that m is NOT 1/1,000,000. you just have to remember what they are.
Also, if I have to memorize all of that I will, but do I really have to remember ALL of that in my head? Just asking. Once again, if I do I will, but if I could just keep not of the important things, that would be great. Thanks.
Remember the shortcut to ohms law. That's a good start.
Keep this list and refer to it if you get confused or if you're uncertain. You may refer to it often at first, but eventually you won't have to refer to it at all.
