What is a Signal — Information in Electrical Form
Signal Foundations
Author: Mark Higgins
© Mark Anthony Higgins 11 October 2025
Revised Date: 19 April 2026
A signal is a representation of information expressed through changes in electrical quantities such as voltage or current. Rather than simply being a physical waveform, a signal encodes meaning within its variation over time.
This page includes an executable teaching flow that can run inside any modern AI system (ChatGPT, Google AI, Claude, and others). It is designed to teach the concept interactively and adapt to your level of understanding.
The more you interact (ask questions, answer checks, request examples), the better the system adapts to you.
Flow: Signal_InformationInElectricalForm_v1_0
Purpose:
Model a signal as a time-varying electrical quantity that carries information, enabling structured teaching of how voltage or current represents, transmits, and transforms information within electrical and electronic systems.
System:
S = (I, R, B, K)
----------------------------------------
Teaching Directive
----------------------------------------
Execution_Mode:
Teaching
Audience:
Beginner to Intermediate learner
Teaching_Flow:
Explain → Visualise → Formalise → Apply
Instruction:
- Begin with intuitive explanation of a signal as a changing electrical value that represents information
- Explain that signals can vary over time in voltage or current
- Relate signals to real-world information such as sound, light, data, or control states
- Introduce the idea that circuits process, transmit, and transform signals
- Reinforce with simple examples such as audio signals, digital signals, and sensor outputs
Constraints:
H = ∅
Clarity before formalism
Goal:
Student understands that:
- a signal is an electrical representation of information
- signals vary over time
- signals can be processed and transmitted through circuits
- signals form the basis of communication, sensing, and control systems
----------------------------------------
State
----------------------------------------
I = {
signal_type,
signal_variable,
amplitude,
time_state,
waveform_shape,
frequency_content,
information_content,
source_origin,
transmission_path,
system_response
}
----------------------------------------
Rules
----------------------------------------
R = {
detect_signal_presence,
identify_signal_variable,
evaluate_time_variation,
map_signal_to_information,
propagate_signal_through_system,
transform_signal,
interpret_signal_output
}
----------------------------------------
Boundaries
----------------------------------------
B = {
signal_requires_time_variation_or_state_change,
valid_signal_variable_required,
transmission_path_required_for_propagation,
signal_must_remain_within_system_limits,
information_mapping_must_be_defined,
no_unphysical_signal_without_source_or state_definition
}
----------------------------------------
Invariants
----------------------------------------
K = {
signal_represents_information_in_electrical_form,
signal_varies_with_time_or_state,
amplitude_encodes_information,
waveform_shape_can_carry_information,
signals_can_be_analog_or_digital,
signals_can_be_transmitted_and_transformed,
interpretation_depends_on_system_context
}
----------------------------------------
Execution
----------------------------------------
E_t = expand(I, R)
V_t = {
x ∈ E_t | x satisfies (B ∧ K)
}
Selection:
x* = argmax_(x ∈ V_t) P(x | I, R, B, K)
Update:
I_(t+1) = update(I_t, x*)
----------------------------------------
Output
----------------------------------------
O = electrical_information_representation_and_transfer | (B, K)
----------------------------------------
Failure Condition
----------------------------------------
V_t = ∅ ⇒ O = FAIL
Meaning:
If no valid time variation, signal variable, or information mapping can be established, no coherent signal representation can be evaluated.
----------------------------------------
Interpretation
----------------------------------------
A signal is an electrical quantity that changes over time or state in a way that represents information. This quantity is usually voltage or current, and its variation encodes meaningful data such as sound, images, measurements, or logical states.
Signals allow systems to communicate, sense the environment, and control behaviour. An audio signal represents sound, a digital signal represents binary data, and a sensor signal represents a physical condition such as temperature or light intensity.
Circuits can transmit signals from one place to another, transform them through amplification or filtering, and interpret them to produce useful outputs. Understanding signals is fundamental to electronics, communication, and control systems.
----------------------------------------
Core Relations
----------------------------------------
Signal = time-varying electrical quantity carrying information
----------------------------------------
Derived Relations
----------------------------------------
Analog signal:
continuous variation over time
Digital signal:
discrete levels representing logical states
Amplitude:
strength of signal at a given time
Frequency:
rate of signal variation
Waveform:
shape of signal over time
----------------------------------------
Teaching Outcome
----------------------------------------
Student can:
- Understand a signal as information in electrical form
- Distinguish between analog and digital signals
- Identify key signal properties such as amplitude and frequency
- Relate signals to real-world information sources
- Recognise how signals are transmitted and processed in systemsVoltage represents the difference in electrical potential between two points—the driving force behind all circuit behaviour.
This section frames voltage as a structured gradient, showing how energy conditions are established, compared, and measured across a system.
Current is the realised movement of charge through a conductive path—the observable expression of system activity.
Here, current is explored as a continuous flow, revealing how charge propagates, how paths constrain movement, and how flow defines system dynamics.
Resistance defines how a system constrains and shapes the movement of charge.
This section examines resistance as an opposition flow—where material structure, geometry, and conditions regulate how easily current can pass.
Power captures the rate at which energy is transferred within a system.
This section explores how voltage and current combine to produce real energy flow, revealing how systems do work, dissipate energy, and operate over time.