1300

Current is

dQ/dt - the rate of flow of charge

Formula for Power (P)

P = V * I = dW/dt

On a diagram, you would draw the current moving

in the flow of the positive charge if they could move, or basically opposite way to the electrons when they’re moving

Kirchoff’s Voltage Law

The sum of Voltage Rises = The sum of Voltage drops

Kirchoff’s Current Law

The sum of current in a node = the sum of current out a node

If voltage and Current arrow are in the same direction

There is negative power —> meaningn supplying power

If voltage and current arrows are in the opposite directions

There is positive power —> power is being dissipated/used

Vbranch = Vy - Vx

where Vy and Vx are nodes

All points connected by a plain wire have the same voltage.

In series, voltage splits across resistors because the same current passes through different resistances, so each resistor uses up a different portion of the total voltage.

current always flows from high voltage to low voltage

nodes are the points where components join, not every corner of the drawing.

For series, Components share one node that only connects those two components (no branching at that point).

For parallel, Both components connect to the same two nodes.

To find Thevenin Resistance

Disconnect all sources and then calculate the resistance looking into the output port

To find Thevenin Voltage

Find voltage across the same node thing, and you can disregard the resistors that are connecting to the output/load line becaues there is no current flowing through them.

Formula for Energy stored in a capacitor

Formula for Energy stored in an inductor

When to use Nodal Analysis

Use when:

• Lots of parallel branches

• Many current sources

When to use Mesh analysis

se when:

• Circuit is mostly series loops

• Mostly voltage sources

• Planar circuit (no weird crossing wires)

Superposition

Use when:

• Multiple independent sources

• You only need one voltage or current

Thevenin Equivalent

V = Vth - I(Rth)

This is when I is leaving the port

A parallel combination is always less than the smallest resistance in that specific parallel group

when you have two current sources in a circuit

use mesh, loko at 2023 exam

Difference between when tryna find Thevenin voltage and I norton when you have either voltage or current source

• Thevenin = “What voltage appears if nothing is connected?”

• Norton = “What current flows if I directly connect the terminals?”

So yes — when finding Norton current, you are literally doing the opposite of Thevenin:

🔄 Open circuit ↔ Short circuit

What are the units for capacitors and inductors

Capacitors = Farads

Inductors = Henries

A practical capacitor does not allow an instantaneous step change in its:

• No instantaneous change in voltage

• No instantaneous change in electric field

A practical inductor does not allow an instantaneous step change in its:

• No instantaneous change in current

• No instantaneous change in magnetic field

capacitor - component law for phasors

Phasor Diagram interpretations

Resistor: The voltage is always in phase with current

Inductor: the voltage is always pi/2 anticlockwise from current, we say that voltage “leads” current

Capacitor: The voltage is always pi/2 clockwise from current, we say that current “leads” voltage

If you increase the frequency for a capacitor /inductor

The impedance decreases and approaches 0, and if you have very low frequency it approaches infinity

Opposite away around for an inductor

What is a transfer function

A transfer function doesn’t “do” anything physically — it describes how the circuit transforms signals.

It tells you:

• How much the signal is amplified or attenuated

• Whether it is inverted

• How it behaves with frequency (e.g. filters)

For example:

• If H=10H = 10H=10, output is 10× bigger → amplifier behaviour

Transfer function formula

Gain(db) formula

An inductor consumes positive VARs

A capacitor consumes negative VARs

VARs consumed = VARs supplied

Qave is positive if reactive load is positive, i.e reactive part of the load is inductive

Qave is negative if reactive load is negative, i.e react part of the load is capacitive

there will be a short answer written question about power, communication and control systems
best past exam papers: 2017 sem 2, 2019, sem 1 2021, sem 1 2024

• X>0 (inductive) → current lags (positive ϕ\phiϕ)

• X<0X < 0X<0 (capacitive) → current leads (negative ϕ\phiϕ)

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explain why electrical power is transmitted over long distances at very high voltages (i.e. 275KV), even though it is generated and utilised at much lower voltages?

Increasing the voltage using a transformer decreases the current by the same factor, thereby minimising I²R power losses in the transmission line

for Transformer

Vp/Vs = Np/Ns

Bang Bang control

Bang-bang control switches between two extreme states only: fully on or fully off

demodulation in AM (amplitude modulated) radio singals

converting a varying high-frequency wave back into the original low-frequency message by extracting its amplitude envelope.

to identify band pass or band stop

series across V out is band stop

Parralel across V out is band pass

if inductor and capacitor are in series - band stop

if inductor and capacitor are in parallel - band pass

formula for resistance in a wire

Briefly (in a sentence or two) explain why electrical power is transmitted over long distances at very high voltages (i.e. 275KV), even though it is generated and utilised at much lower voltage

lossess in transmission lines is proportional to I²

transmitting at very high voltages minimises I (for a given power delivery) and therefore minimises transmission line losses

proportional control in context of car cruise control

driver sets desired speed

spedometer measures acutal speed

the error (difference in speed) is calculated and throttle is set proportionally to current error, i.e throttle setting adjustment is proportional to error.

energy = V * I multiply (time)

In a sentence or two, describe a practical example of an electronic filter that is used to remove noise from an electronic signal of interest. You should explicitly state the filter type and the describe the frequency characteristics of the noise that is removed and the signal that is preserved.

In an AM radioreciever a band pass filter is used to slect the desircd radiochanne

op amp formula for inverting

-Rf/Rin

op amp formukla for non inverting

1 + Rf/Rin