## **Main topics:** Introduction, Basic concepts, Ohm’s law

- pass the circuit labs
	- mandatory!
- 2 partial exams
	- trial exam week 4
- 6 SGH's --> only best 5 count
	- bonus points --> dewit
	- check [Brightspace](https://brightspace.tudelft.nl)

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# Content
Syllabus on [Brightspace](https://brightspace.tudelft.nl)
- Dc circuits
	- Basis
	- electrical elements
	- circuit analysis methods
- Dynamic circuits
	- end of q1 with Time-domain solutions


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# Actual lecture
#OhmsLaw 
## The basis
- Volta --> sustained electrical stimulus "Volta Pile"
- move cells ("More Volts") --> more "energetic" a stimulus
- nr of volts = voltage
- **one always needs 2 points for tapping the energy**
- Voltage -> 2 access points
- An electric current deflects a magnetic needle
- galvanometer --> precise method for measuring electric currents
	- measures current and uses fancy math to measure volts
- two basic, easily measurable quantities
	- voltage + current
- Pairs of access points
	- at which the supplied energy
	- between which the current
			**Both can be unambiguousy measured** (predicted)
	 = ports
	Circuit analysis = the analysis of the relations between voltages and currents at given ports
	
We study circuits
- made from electrical elements (lumped elements , idealized)
- connecting wires (ideally 0 v over the wires)


### Si system
current -> Ampere
Charge -> s\*A -> Coulomb (C)
electrical potential -> volt

Charge = an electrical property of sub-atomic constituents measured in Coulomb (C)
charge of electron = e = -1.6 \* 10^-19 C
Electric current: a measure of the temporal variation of the electric charge, measured in A(mpere)

$$
i = \frac{dq}{dt} \newline

$$

DC = a current that remains constant with time
AC = current that varies sinusoidally with time

A positive value for the current indicates a flow in the direction of the arrow (reference direction)
 a negative value -- \\ -- in the opposite direction of the arrow

the potential difference between two points is denoted as voltage

the potential is the electrical potential energy per unit charge

$$
V_ab = \frac{w}{q}
$$

Voltage --> across
Current --> through


power = energy/time

instantatneous power = p = dw/d = dw/dq \* dq/dt = v\*i
energy -> power (iintegration)

$$
w(t) = \int 
$$

if voltage and current are both positive --> the positive charges move from a higher potential to a lower potential (in the direction of the current) (from + to -)

The component absorbs power --> passive component

\
### Resistance and ohms law
- ratio v(t)/i(t) at the same time instant t
- = elements ability to resist the flow of electric current
- wire like conductors 
$$ R = \rho \cdot \frac{l}{A} \newline $$
$$ \rho = resitivity $$
$$ l = length\ of\ wire $$
A = cross-sectional area

conductance = reciprocal or resistance
\[G\]  = S(iemens)
$$ G = \frac{1}{R} = \frac{i}{v} $$
most materials have non-linear resistance