Edexcel • 1PH0 • 1,246 key terms
100% efficiency
A state where the total power input to a device is exactly equal to its useful power output, with no wasted energy.
From: Transformer Power Equation
Absolute temperature
A measurement of temperature related to the thermal energy of a body, where zero represents absolute zero, the point at which all objects still emit radiation if they are above it.
From: Emission and Temperature
Absolute zero
The lowest possible temperature (-273°C or 0 K) at which the particles of a substance have zero kinetic energy and theoretically stop moving.
From: Kelvin and Celsius
Absorber
A surface that takes in thermal radiation, causing its internal energy and temperature to increase.
From: Core Practical: Thermal Radiation
Absorption
The process where an electron takes in energy from electromagnetic radiation to move to an orbit further from the nucleus.
From: Orbit Changes
Absorption lines
Dark lines in a continuous spectrum caused by specific elements in a star's atmosphere absorbing certain wavelengths of light.
From: Evidence for Big Bang
Absorption spectra
The patterns of dark lines in a continuous spectrum, which are used to detect red-shift by comparing them to a stationary reference source.
From: Theories and Red-shift
Absorption spectrum
A spectrum of electromagnetic radiation transmitted through a substance showing dark lines where specific wavelengths have been absorbed.
From: Expansion Evidence
Acceleration
A vector quantity defined as the rate of change of velocity.
From: Vectors and Scalars
Acceleration due to gravity
The constant acceleration of an object in free fall near the Earth's surface, which has a value of 10 m/s².
From: Acceleration due to Gravity
Acetate rod
A common insulating material used in experiments that loses electrons and becomes positively charged when rubbed with a cloth.
From: Electron Transfer
Action-Reaction Pair (N3L Pair)
Two forces representing the mutual interaction between two different bodies that are equal, opposite, and of the exact same type.
From: Newton's Third Law and Momentum Conservation
Activity
The rate at which a source of radioactive material decays, representing the number of decays per second.
From: Nuclear Energy Sources
Additional path
A newly created branch in a parallel circuit that allows more current to flow, thereby lowering total resistance.
From: Core Practical: Electrical Circuits
Aerial
A metal conductor (antenna) used to either transmit radio waves into the air or receive them.
From: Radio Waves and Circuits
Airbags
Compressible cushions in vehicles that deploy during a crash to increase the contact time for a passenger's head or torso to come to rest.
From: Force and Change in Momentum
Air resistance
A type of frictional force caused by air pushing against a moving object, dissipating kinetic energy into thermal energy.
From: Closed Systems
ALARP principle
The safety protocol of keeping radiation exposure "As Low As Reasonably Practicable" to minimise biological risks.
From: Safety Precautions
Alpha
A type of ionising radiation consisting of two protons and two neutrons (a helium nucleus); it has high ionising power but low penetrating power.
From: Contamination vs Irradiation
Alpha decay
A type of radioactive decay where an unstable nucleus emits an alpha particle, decreasing its mass number by 4 and atomic number by 2.
From: Balancing Nuclear Equations
Alpha emitter
A radioactive substance that decays by releasing alpha particles, which consist of 2 protons and 2 neutrons.
From: Origins of Background Radiation
Alpha particle
A highly ionising, low-penetration particle consisting of two protons and two neutrons, identical to a helium nucleus.
From: Uses of Radioactivity
Alpha radiation (α)
A type of strongly ionising radiation consisting of two protons and two neutrons (a helium nucleus).
From: Comparison of Radiations
Alternating current
An electric current that periodically reverses direction and changes its magnitude continuously with time.
From: Uses of Radio Waves, Microwaves and Infrared
Alternating current (a.c.)
An electric current that continuously changes its direction of flow.
From: Alternators and Dynamos
Alternating current (AC)
An electric current that continuously reverses its direction and changes its magnitude in a cyclical manner.
From: Radio Waves and Circuits
Alternating magnetic field
A magnetic field that continuously changes its direction and strength, produced by an alternating current.
From: Transformer Induction
Alternating potential difference
A potential difference that fluctuates in magnitude and periodically reverses in direction.
From: Live and Neutral Wires
Alternating voltage
A potential difference that continuously changes direction and magnitude over time.
From: Transformer Voltage
Alternator
A type of generator that uses continuous slip rings to produce an alternating current (a.c.).
From: Alternators and Dynamos
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