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

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Content

Syllabus on Brightspace

Dc circuits
- Basis
- electrical elements
- circuit analysis methods
Dynamic circuits
- end of q1 with Time-domain solutions

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

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