AQA As Physics A Definitions for unit 2

List of all the definitions needed for AQA unit 2 physics.

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Stress tension per unit cross sectional area.
Strain ­ extension per unit length.
Young modulus ­ Stress/strain ( as long as the limit of proportionality has not been reached).
Limit of proportionality ­ The limit beyond which, when a wire or a spring is stretched, its extension is no
longer proportional to the force that stretches it.
Elastic limit ­ point beyond which a wire is permanently stretched.
Yield point ­ the point at which stress in a wire suddenly drops when the wire is subjected to increasing
Ultimate Tensile Stress (UTS)/ Breaking stress ­ Tensile stress needed to break a solid material.
Plastic Deformation ­ deformation of a solid beyond its elastic limit.
Elasticity ­ property of a solid that enables it to regain its shape after it has been deformed of distorted.
Hooke's Law the force needed to stretch a spring is directly proportional to the extension of the spring
from its natural length.
Density mass per unit volume.
Amplitude ­ the maximum displacement of a vibrating particle for a transverse wave, it is the distance from
the middle to the peak.
Longitudinal Waves Waves with a direction of vibration parallel to the direction of propagation of the
Transverse Waves Waves with a direction of vibration perpendicular to the direction of propagation of
Planepolarised waves ­ Transverse waves that vibrate in one plane only.
Wavelength ­ the least distance between two adjacent vibrating waves with the same displacement and
velocity at the same time.
One complete cycle of a wave is from maximum displacement to the next maximum displacement.
Period the time for one complete wave to pass a fixed point.
Frequency the number of cycles of vibration of a particle per second. Unit of frequency is hertz (Hz).
Phase difference ­ the fraction of a cycle between the vibrations of two vibrating particles, measured in
radians or degrees.
Wavefronts ­ lines of constant phase.
Refraction change of direction of a wave when it crosses a boundary where its speed changes.
Superposition ­ the effect of two waves adding together when they meet.
Stationary waves ­ wave pattern with nodes and antinodes formed when two or more waves of the same
frequency and amplitude pass through each other.
Node ­ fixed point in a stationary wave pattern where the amplitude is zero
Antinode ­ fixed point in a stationary wave pattern where the amplitude is a maximum.
Interference ­ formation of points of cancellation and reinforcement where two coherent waves pass
through each other.
Coherent two sources of waves are coherent if they emit waves with a constant phase difference.
Path Difference ­ the difference in distances from two coherent sources to an interference fringe.
Fundamental mode of vibration ­ pattern of stationary waves on a string when it vibrates at its
fundamental (lowest possible) frequency.
First overtone ­ where there is a node in the centre. ( 1 node)
Second overtone Where there are 2 nodes.

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Refractive index ­ Speed of light in free space / speed of light in a substance ( c(vacuum)/c(material), sini/sinr,
Total internal reflection ­ A light ray travelling in a substance is totally internally reflected at a boundary
with a substance of lower refractive index, if the angle of incidence is greater than a certain value known as
the critical angle.
Critical angle ­ the angle of incidence of a light ray must exceed the critical angle for total internal
reflection to occur.…read more


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