Key Words

Conductors

A material that allows the flow of electrical charge. Good conductors have a larger amount have free charge carriers to carry a current.

Conservation of Charge

The total charge in a system cannot change.

Conventional current

The flow from positive to negative, used to describe the direction of current in a circuit

Coulomb

The unit of charge. 1 Coulomb is the amount of charge that flows past a point when 1 Amp of current flows for 1 Second.

Electric Current

The rate of flow of charge in a ciruit

Electrolytes

Substances that contain ions that when dissolved in a solution, act as charge carriers and allow current to flow

Electron Flow

The opposite direction to convention current flow. Electrons flow from negative to positive

Elementary Charge

The smallest possible charge, equal to the charge of an electron

Insulators

A material that has no free charge carriers and so doesn’t allow the flow of electrical charge

Kirchhoff’s First Law

A consequences of the conservation of charge. The total current entering a junction must equal the total current leaving it.

Mean Drift Velocity

The average velocity of an electron passing through an object. It is proportional to the current, and inversely proportional to the number of charge carriers and the cross-sectional area of the object

Quantisation of Charge

The idea that charge can only exist in discrete packets of multiples of the elementary charge

Semiconductors

A material that has the ability to change its number of charge carriers, and so its ability to conduct electricity. Light dependent resistors and thermistors are both examples

Diode

A component that allows the current through in one direction only.

Electromotive Force

The energy supplied by a source per unit charge passing through the source, measured in volts

Filament Lamp

A bulb consisting of a metal filament, that heats up and glows to produce light. As the filament increases in temperature, its resistance increases since the metal ions vibrate more and make it harder for the charge carriers to pass through

I-V Characteristics

Plots of current against voltage, that show how different components behave

Kilowatt-Hour

A unit of electrical energy. It is usually used to measure domestic power consumption

Light-Dependant Resistor

A light sensitive semiconductor whose resistance increases when light intensity decreases

Ohm

The unit of resistance

Ohmic Conductor

A conductor for which the current flow is directly proportional to the potential difference across it, when under constant physical conditions

Ohm’s Law

The current and potential difference through an ohmic conductor held under constant physical conditions are directly proportional, with the constant of proportionality being resistance

Potential Difference

The difference in electrical potential between two points in a circuit. It is also the work done per Coulomb to move a charge from the lower potential point to the higher potential point. It is measured in volts.

Power

The rate of energy transfer in a circuit. It can be calculated as the product of the current and the potential difference between two points. It is measured in Watts

Resistance

A measure of how difficult it is for current to flow through a material

Resistivity

A measure of how difficult it is for charge to travel through a material. It is proportional to the object’s resistance and cross-sectional area, and inversely proportional to the object’s length. It is measured in Ohm metres

Resistor

A device that has a fixed resistance and follows Ohm’s law

Volt

The unit of potential difference

Conservation of energy

Energy cannot be created or destroyed- it can only be transferred into different forms

Internal Resistance

The resistance to the flow of charge within a source. Internal resistance results in energy being dissipated within the source

Kirchhoff’s Second Law

A consequence of the conservation of energy. The sum of the voltages in any closed loop must equal zero

Lost Volts

The difference between a source’s emf and the terminal voltage. It is equal to the potential difference across the source’s internal resistance

Parallel Circuit

Components are said to be connected in parallel when they are connected across each other (separate loops)

Potential Divider

A method of splitting a potential difference, by connecting two resistors in series. The total potential difference is split in the ratio of their resistances

Resistors in Parallel

The potential difference across resistors connected in parallel is identical for each resistor. The current is split between the resistors. The total resistance is equal to the inverse sum of the inverses of the resistances of the resistors

Resistors in Series

The current through resistors connected in series is identical for each resistor. The potential difference is split in the ratio of their resistances. The total resistance is equal to the sum of the resistances of the resistors

Sensor Circuits

A circuit that reacts to external conditions. They commonly involve a semiconductor connected in a potential divider arrangement

Series Circuit

Components are said to be connected in series when they are connected end to end (in one loop)

Terminal PD

The potential difference across the terminals of a power source. It is equal to the source’s emf minus any voltage drop over the source’s internal resistance

Amplitude

A wave’s maximum displacement from its equilibrium position

Antinodes

A position of maximum displacement in a stationary wave

Coherence

Waves with the same frequency and constant phase difference

Constructive Interference

The type of interference that occurs when two waves meet in phase. The wave amplitudes are superposed

Critical Angle

The angle of incidence that results in an angle of refraction of exactly 90^o. It is when the refracted ray travels along the boundary line.

Destructive Interference

The type of interference that occurs when the two waves are in antiphase. When one wave is at a peak and one is at a trough their addition results in a minimum point

Diffraction

The spreading of waves as they pass through a gap of a similar magnitude to their wavelength

Displacement

The distance that a point on a wave is from its equilibrium position

Electromagnetic Spectrum

The spectrum of electromagnetic waves

Electromagnetic Waves

Waves that consist of perpendicular electric and magnetic oscillations. All electromagnetic waves travel at the speed of light in a vacuum.

Frequency

The number of waves that pass a point in a unit time period. It is the inverse of the time period.

Fundamental Mode of Vibration

The oscillation of a wave at its natural frequency

Intensity

The power transferred per unit area. It is proportional to the square of a wave’s amplitude.

Interference

The superposition of the amplitudes of waves when they meet

Longitudinal Waves

A wave with oscillations that are parallel to the direction of energy propagation. Cannot travel through a vaccum

Nodes

A position of minimum displacement in a stationary wave

Oscilloscope

A device used to display and analyse waveforms

Path Difference

A measure of how far ahead a wave is compared to another wave

Period

The time taken for a wave to complete one full cycle

Phase Difference

The difference in phase between two points on a wave. It is usually expressed in radians

Polarisation

The restriction of a wave so that it can only oscillate in a single plane. This can only occur for transverse waves

Progressive Waves

Waves that transfer energy from one point to another without a transfer of matter

Reflection

The bouncing of a wave at a boundary. The angle of incidence will equal to the angle of reflection

Refraction

The changing of speed of a wave as it passes into a new medium. If it passes into an optically denser medium, it will slow down

Refractive Index

A material property that is equal to the ratio between the speed of light in a vacuum, and the speed of light in a vacuum and the speed of light in a given material

Stationary Wave

A wave that stores, but does not transfer, energy

Superposition

When two waves meet at the same point in space their displacements combine and the total displacement at that point becomes the sum of the individual displacements at that point

Total Internal Reflection

An effect that occurs in optical fibres, where full reflection occurs at the inside boundary of the fibre, meaning no radiation passes out. The angle of incidence must be greater than the critical angle for this to occur

Transverse Waves

Waves with oscillations that are perpendicular to the direction of energy propagation.

Wave Speed

The product of a wave’s frequency and wavelength

Wavelength

The distance between two identical positions on two adjacent waves. It is commonly measured from peak to peak or trough to trough

Young Double-Slit Experiment

An experiment that demonstrates the diffraction of light by passing monochromatic light across two narrow slits and observing the resulting pattern of bright and dark fringes