Electrons, Waves and Photons definitions Flashcards
Conductors
A material that allows the flow of electrical charge. Good conductors have a larger amount of free charge carriers to carry a current
Conservation of charge
The total charge in a system cannot change
Coulomb
The unit of charge
Electric current
The rate of flow of charge in a circuit
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 conventional 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 consequence 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 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 current through in one direction only. In the correct direction, diodes have a threshold voltage (typically 0.6 V) above which current can flow
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 shows how different components behave
Kilowatt-Hour
A unit of electrical energy. It is usually used to measure domestic power consumption
Light-Dependent 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 length and cross-sectional area. 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 terminal voltage. It is equal to the potential difference across the source’s internal resistance
Parallel circuits
Components are said to be connected in parallel when they are connected across each other in 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
Sensor circuits
A circuit that reacts to external conditions. They commonly involve a semiconductor connected in a potential divider arrangement
Series Circuits
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 degrees. It is when the refracted ray travels along the boundary line
Destructive interference
The type of interference that occurs when 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, consisting of Gamma rays, X-rays, Ultraviolet, Visible light, Infrared, Microwaves and Radio 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. Sound waves are an example of a longitudinal wave. They cannot travel through a vacuum
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, usually expressed in terms of the wavelength
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 measured in radians
Polaristation
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 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 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
A wave with oscillations that are perpendicular to the direction of energy propagation. Electromagnetic waves are examples of transverse waves
Wave speed
frequency x 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
