# AQA As Physics A Definitions for unit 2

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

- Created by: Olivia Marland
- Created on: 31-05-11 11:22

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Definitions

Materials

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

strain.

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.

Waves

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

waves.

Transverse Waves Waves with a direction of vibration perpendicular to the direction of propagation of

waves.

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.

Optics

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