Current, Voltage, and Energy Flow in Circuits

Charge

one of the basic properties of the elementary particles (electrons and protons) which can be positive or negative and occurs in whole number units.

Conservation of charge

The net amount of charge produced in any transfer process is zero.

Like charges

repel each other.

Unlike charges

attract each other.

Conductors

Metals are good electrical conductors because any charge placed on them is free to move throughout the atom.

Insulators

Substances that do not allow free charge movement - outer electrons are tightly bound to the atoms - Poor conductors of electricity.

Semiconductors

Their conductivity is variable - they can behave as insulators or conductors.

Superconductors

Materials that acquire infinite conductivity (zero resistance to the flow of charge) usually at very low temperatures.

Coulomb

a measure of electric charge.

Electric charge measurement

Electric charge is measured in units called coulombs named after French physicist Charles-Augustin Coulomb.

Charge on a single electron

1.6 x 10^-19 C.

Voltage

a measure of electric potential energy per unit charge, measured in joules per coulomb; often referred to as electric potential.

Volts

a unit of electrical potential or voltage, equivalent to 1 joule per coulomb of charge.

Electric current

the rate of motion of electric charge.

Current formula

I = charge (q) / time (t).

Ampere

One ampere of electric current is a flow of charge of 1 coulomb per second.

Charge calculation example

Calculate the charge in coulombs of 1.25 x 10^25 electrons: 1.6 x 10^-19 x 1.25 x 10^25 = 2 x 10^6 C.

Charge in coulombs of electrons

Calculate the charge in coulombs of 6.02 x 10^23 electrons.

Current example

A charge of 30C passes through a light bulb in 1 minute. What was the current in the bulb?

Conventional Current

The motion of positive charges from positive to negative, opposite to electron flow.

Electron Flow

The direction of actual electron flow is from negative to positive.

Direct Current

When electric current flows from the source of a charge around a circuit in one direction, with constant magnitude and direction over time, e.g., batteries.

Alternating Current

Oscillating current flow in two directions, e.g., household electricity.

Ammeter

An instrument used to measure current through a component in electric circuits.

Voltmeter

An instrument used to measure voltage across a component in electric circuits.

Multimeter

An instrument that can measure current, voltage, and resistance in a circuit.

Electric Potential

The amount of work needed to move a unit charge from one point to another, measured in Joules per Coulomb.

Electric Potential Energy

The energy stored in a charge or the capacity of the charge carriers to do work due to their position.

Potential Difference

The difference between two electric potentials, measured in volts (V), usually referred to as the electromotive force (EMF) of the cell.

Electric Potential Formula

V = W/q, where V is electric potential, W is work done, and q is charge.

1 Joule per Coulomb

Equal to one Volt.

Coulombs of Charge Calculation

The total charge can be calculated using the number of electrons flowing, where 1 electron = 1.6 x 10^-19 coulombs.

Current Calculation

Current in amperes can be calculated by dividing the total charge (in coulombs) by the time (in seconds) it takes for that charge to flow.

Work Done on Charge

If 1 joule of work is done on 1 coulomb of charge, the electrical potential is increased by 1 volt.

Negligible Effects of Meters

Ammeters and voltmeters require current to operate but have negligible effects on the current and voltage.

Electricity and Electrostatics History

Experiments with electricity and electrostatics were conducted before the discovery of electrons, assuming positive charges were moving.

Current Measurement

Current is measured in amperes (A).

Voltage Measurement

Voltage is measured in volts (V).

Resistance Measurement

Resistance is measured in ohms (Ω).

Household Electricity

Typically refers to alternating current (AC) that oscillates in two directions.

Battery Current

Batteries provide direct current (DC) that flows in one direction.

Work-Energy Principle in Electricity

It requires work to be done on a positive charge to pull it away from a negative charge, similar to moving an object against gravity.

Work done

The energy transferred when a charge moves through an electric potential difference, calculated as W = V x q.

Electrical Power

The rate of energy transfer or the rate at which electrical work is done, given by P = W/t.

Watt

The unit for electrical power, equivalent to one Joule per second.

Resistance

The opposition to the flow of electrical current in a circuit, measured as the ratio of voltage to current.

Ohm's Law

A principle stating that the current through a conductor between two points is directly proportional to the voltage across the two points, expressed as V = I x R.

Ohmic Device

A device that follows Ohm's Law, where the current is directly proportional to the voltage.

Non-Ohmic Device

A device that does not follow Ohm's Law, where the resistance changes with voltage or current.

Fixed Resistor

A resistor with a constant resistance value that does not change.

Variable Resistor

A resistor whose resistance can be adjusted.

Gradient

The slope of a graph representing the relationship between two variables, such as current and voltage.

Electric Potential Difference

The difference in electric potential between two points, which drives the flow of current.

Energy Transfer

The process of converting electrical energy into other forms of energy, such as heat or light.

Joule

The unit of energy, equivalent to the work done when a force of one newton displaces an object by one meter.

Amperes

The unit of electric current, defined as one coulomb per second.

Voltage Controlled Switch

A device that operates based on a specific voltage threshold, turning on or off at that voltage.

Transistor

A semiconductor device used to amplify or switch electronic signals and electrical power.

Diode

A semiconductor device that allows current to flow in one direction only.