Section One Flashcards
What are three popular ways to measure electricity?
volts
amps
watts
What is an atom made of?
protons (positive charge)
and
neutrons (no charge)
are part of the nucleus
electrons (negative charge)
surround the nucleus
What is an atomic number?
The number of protons in an atom
For instance, plutonium has 94 protons in the atom
A copper atom has 29 protons? How many electrons does it have?
Why?
29 usually
Each proton attracts a electron
What are the electrons on the outer orbit of an atom called?
Valence electrons
These can hop around to other atoms.
Copper has a valence electrons that we use to make electrical current because it’s easy to move
What is used to move electrons?
Voltage - a pushing force, it’s like water pressure
What causes positive or negative charge?
An atom loses an electron or two making it positively charged and vice versa
What makes copper a good choice to make electrical current?
It has a valence electron that can be moved easily, in fact, it does this on it’s own, but the electron doesn’t follow a certain path
What causes electric current?
A force that acts on electrons (EMF) Electromotive force and its quantity is voltage
What are the following on falstad.com/circuit/circuitsjs.html in terms of the osciloscope at the bottom of the bottom:
green
yellow
yellow dots
green line - Voltage across component
yellow line - Current
yellow dots - electrons/current flowing
In terms of a fun example:
What is voltage?
What is resistance?
What is amps?
Voltage can be thought of as motivation
If you have place A and it’s too expensive, and place B that is super cheap, lots of people will be able to move there.
If you consider the price of flight tickets as resistance, if flight tickets are cheap, the more people will be able to go so the people moving every day will be current/amps.
Using a fun example, what’s a way to think of resistors in parallel vs series?
In parallel - The resistors mean two more flights, so motivation to leave is still the same, but more people can travel at once
In series - It’s more difficult to get from point A to point B because there is still one flight that goes there, but you also have to take a connecting flight, this decreases current (amount of people moving a day.)
What is the difference between these two symbols
____ _____
– –
____
–
The first is a Battery Cell
The Second is a Battery
A battery is a collection of cells
What is DC
What is AC
Direct Current
Alternating Current
How do you measure Amps with your multi-meter?
Break a part of the circuit and insert your probes in the positive and negative to complete the circuit
What is voltage in technical terms
The potential difference between two points
Ground = 0V
Positive = 5V (in a 5V battery)
So the voltage from positive to ground is 5V because 5 - 0 = 5
What is an Ohm
1 ohm is the resistance between two points where 1V of applied potential energy will push 1 ampere of current
What doe the color bands indicate?
4-6 bands
band 1 and 2 most significant digits
3rd band multiplier
4th tolerance (if 5% it could be 5% off)
How do Ohms work in parallel versus series?
parallel - 2 1k res will give you 400 k each
1/r = 1/r1 1/r2
series - 2 1k res will give you 2k res
r+r
Calculator resistors in a parallel circuit with
4 ohms
5 ohms
20 ohms
1/4 = .25
1/5 = .20
1/20 = .05
1/.50 = 2
2 ohms
Why do we calculate total resistance?
We can get total current
now we know how long the battery will last
What is voltage drop?
5V of battery can do 5 joules of work per coulomb of charge.
When current flows through a resistor we can measure the amount of work (per unit of charge) required to keep the current flowing through the resistor.
When current is flowing, components like resistors consume energy, the amount of work per unit charge associated with the current flowing through a give component is the component’s voltage drop.
The voltage dropped by a component accounts for a portion of the voltage generated by the battery. So the work performed by the battery is divided up among the components in the circuit.
Load - component that consumes energy
The voltage needs to drop before ground or we’ll get an explosion ie. a short circuit
What is a voltage divider?
Use this circuit to explain it
5V power supply
2 1K resistors
It causes the voltage to drop to a certain amount.
5V with two 1k resistors has a 2.5mA current (5V/2kR=2.5mA or .0025)
Since we have 2 resistors, lets find voltage drop from the first
.0025 * 1k = 2.5
So it drops 2.5 and when it hits the next one it will drop another 2.5
This is known as a voltage divider
2.5V is between the resistors
If we have a 5V battery, which value resistors would we use to create a voltage divider that produces 3V
Vout = Vin * (r2/r1+r2)
Vout - voltage out
Vin - voltage in
If there’s a signifigant amount of current flow through the load this doesn’t work
What is a load?
Device that takes electrical energy, it consumes current and turns it into heat, light, etc
Resisters converts energy into heat, so the more electricity passing through, the hotter it gets.
If your voltage divider has two resistors working for it, how much does the voltage drop?
5V and 2 100Rs
What happens if you connect a load of 150 ohms in the middle and have it connect to the other end of the 2nd resistor
like this 5V ———–
|
R1 100 Ohms
——-
| load 150 Ohms
——– R2 __ Ohms
It always cuts it in half
The smaller ohms the 3rd resister gets, the more current but less voltage
The opposite is true if you increase the Ohms. This makes sense if you calculate the parallel resistance and get the total resistance.
Vout = Vin * R2 || RL(load)
———————
R1 + R2 || RL
This is because R2 is in parallel with RL
CALCULATE THE PARALLEL FIRST
1/Req = 1/R2 + 1/RL
Which is equal to:
Req = R2 * RL
————
R2 + RL
|| <- parallel
Req - R equals
SCRATCH ALL OF THAT
Do the original equation
Vout = Vin * R2/(R1+Total resistance of R2) which is in parallel so
1/req = 1/r2 + 1/rl
vin * R2/Req
Calculate the voltage leaving the Voltage Divider
like this 5V ———–
|
R1 100 Ohms
——-
| load 150 Ohms
——– R2 100 Ohms
Equation:
Vout = Vin * (r2/r1+r2)
But first we grab the amps of the entire circuit
5/160 = 3.1 Volts leaving the voltage divider
Load and R2 are parallel so we do that first
1/Req = 1/100 + 1/150 = .01 + 0.006 = 1 / .016 = 62.5
Let’s round that to 60Ohms
Now we add R1 and R2
100 + 60 = 160
Now we divide R2 by that
100 / 160 = 0.625
Now we multiply the voltage leaving the divider by our output
3.1 * 0.625
0.031
