--title Electricity - Direct Current
--author 
--newpage
--beginslideleft
Water
--endslideleft
--image image/wasserfall_real
--newpage
--heading Water Model (Fluid Model)
* Water Molecules
* Pipes
* Current

Continuity Equation
A_1⋅v_1=A_2⋅v_2.

What goes in comes out.
--newpage
--heading Electrostatics
* Electrons (usually)
* Conductors
* Current

--image image/electron_cloud

Continuity Equation
ΣQ=const. Total charge is const.
Σ(dQ/dt)=0. Total current is 0.
ΣI=0. Total current is 0.
What goes in comes out.

--newpage
--heading Potential

* Why does almost no water current flow in this case?

--image image/wasser_grade

--newpage
--heading Potential

* Why does a strong water current flow in this case?

--image image/wasserfall_real

--newpage
--heading Electric Potential

* Why doesn't a current flow in this case?
* Why does it in this case?
--newpage
--heading Electric Voltage

* How is the current affected by potential?
--newpage
--heading Resistance

Real conductors do not conduct electricity in an ideal way.
We say that they have "resistance" to the current, they impede the current.
Conducting wire only has little resistance, that's why it's called "conducting wire".
There are special kinds of wire having a lot of resistance, these are called "resistors".

--heading Resistors

[real picture]
--image image/resistors_real

[diagram picture]
--image image/resistors_diagram

--newpage
--heading Ohm's law

Most resistors affect the current I in a way that is (almost) proportional to the voltage U.
The energy sucked off is usually released into the environment as heat.

U=R⋅I

where
R:=ρ⋅s/A
ρ specific resistance (material constant).
s length
A area

--newpage
--heading Water Networks

Parallel elements
Serial elements
--newpage
--heading Electrical Networks (Circuits)

Parallel elements
--image image/resistors_in_parallel

--newpage
--heading Electrical Networks (Circuits)

Serial elements
--image image/resistors_in_series

--newpage
--heading Kirchhoff Laws
1. The sum of all currents in a node* is 0. What flows in flows out.
* well, by node one usually means a crossing of circuit lanes. Although it holds on almost any point, most useful is the crossing point.

--image image/node

2. The total potential difference** in a closed loop is 0. The voltage in any closed loop is 0.
** since it is a loop, these have to have a sign, otherwise how would it be a loop?

--image image/loop

--newpage
--heading Circuits

* Resistors in series:

R=R_1+R_2

* Resistors in parallel:

--image image/equation/parallel_1.png
--image image/equation/parallel_2.png

--newpage
--heading Conventions

Current flow:
* Technical direction: positive to negative terminal (hi Franklin)...
* Real direction (well, mostly): negative to positive terminal (electrons move to the positive terminal).

The world became used to the technical direction by now.

--newpage
--heading Measuring

* Voltmeter: in parallel. Non-invasive.
* Amperemeter: in series. Invasive.

! Measurement changes the thing measured. !

--newpage
--heading What?! Only resistors?

* Voltage divider without load
--image image/spannungsteiler

--newpage
--heading What?! Only resistors?

* Voltage divider with load
--image image/spannungsteiler_last

--newpage
--heading What?! Only resistors?

* Lamp: resistor.
* Loudspeaker: resistor.
* Engine: resistor.
* Heater: resistor (well obviously).

--newpage
--heading Okay okay so there are other elements, too.

* Condenser (Capacitor): like a connection, until it's full. Then like an interruption.
* Coil: like an interruption.

--newpage
--heading LEDs

[real picture]
--image image/LED_throwies

[diagram picture]
--image image/LED_diagram

LEDs are elements that emit light (Light-Emitting Diode).

A specific current (specific to the LED type) should flow through the LED.
The easiest way to achieve that is to add a resistor in series.
Never use a LED without any resistor.

1) most of the time, I_L=20mA (for 5mm LEDs).
--rem 2) [U_L = {1.9V, red
--rem           2.2V, green|yellow
--rem           3.0-4.0V, white|blue}*random(1)]
2) R = (U_V-U_L)/I_L
3) P_R_max = 0.25W..0.5W
4) LEDs block current in one direction, max. voltage before they break: 5V.

--newpage
--heading Astable Multivibrator

--image image/astable_multivibrator

--newpage
*

--newpage
--beginslideright
--image image/resistance_is_futile
Widerstand ist zwecklos.
Resistance is futile.
--endslideright
--newpage

http://www.falstad.com/circuit/
--exec firefox http://www.falstad.com/circuit/