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Absolute refractive index
Property of the optical material equal the ratio : speed of light in a vacuum/speed of light in the material

Acceleration
The rate of change of velocity : change in velocity/time taken ; unit m s^{2}

Acceleration due to gravity
The rate at which all objects Accelerate under gravity if air resistance is neglected ; also known as the acceleration of free fall ; on earth its usually taken as 9.81 m s^{2} , but it varies slightly from place to place

Amplitude
The maximum height of a wave , or the largest displacement from equilibrium

Anti node
A point on a standing wave where the amplitude is at a maximum

Anti phase
Two points on a wave , or points on two waves , are in anti phase if their vibrations are 180° out of phase with each other

Breaking stress or ultimate tensile stress
The maximum stress (force per unit area) that a material can withstand before it breaks

Brittle
A brittle material fractures before it undergoes plastic deformation

Centre of gravity
The point at which the weight of an object can be taken to act ; an object will balance if its supported at its centre of gravity

Centre of mass
The point at which the mass of an object can be taken to be concentrated ; in a uniform gravitational field this is the same as the centre of gravity

Cladding
A layer of glass (or plastic) that surrounds the central core of an optical fibre

Coherent
Two or more waves that have a fixed phase difference are said to be coherent

Component
A vector can be split up into perpendicular components ; the vertical component is the part of the vector that acts in a vertical direction

Compression
An object in compression is under the influence of forces that tend to squash it

Coplanar forces
A two dimensional system of forces that all act in the same plane ; they can be drawn on a piece of paper

Couple
Two equal forces that act in opposite directions on an object so as to cause rotation

Critical angle
The minimum angle of incidence at an optical boundary at which total internal reflection occurs

Density
The amount of mass per unit volume

Diffraction
The spreading of waves through an aperture or round an obstacle

Diffraction grating
A series of closely spaced parallel slits through which light can diffract ; used to create spectra

displacement
a vector describing the difference in position of two points

Drag
Resistive force , such as air resistance , which acts to oppose motion in a fluid

Ductility
The ability of materials to show extended plastic deformation and become elongated under tension ; a ductile metal can be drawn out into wires

Efficiency
The ratio : useful energy transferred (or work done) / total energy input ; this is always less tHan 10

elastic behavIour (elasticity)
When a material returns to its original dimensions after deforming force is removed

Elastic strain energy
The potential energY stored in an elastic material that has been extended

Endoscope
A medical device that used optical fibres to see inside the body

energy
The ability to do work I.e. Move a force through a distance ; a scalar quantity , measured in joules

Equilibrium
An object is said to be in equilibrium if its not accelearting

First order maximum
A point at which the waves passing through a diffraction grating interfere constructively ; waves from adjacent slits have a path difference one wavelength , and so all to wave arrive in phase

Free body diagram
A simplIfied picture of a physical situation which shows all of the relevant forces acting on a body

Frequency
The number of waves passing a point in one second , measured in hertz , Hz

Friction
A force that acts between surfaces , acting so as to oppose their relative motion

Fundamental frequency
The lowest resonant frequency of a vibrating system or a standing wave

Gravitational potential energy
The energy stored by a mass due to its position in a gravitational field ; in a uniform field ,the gravitational potential energy of a mass , m , that is raised by a distance , delta h , is given by E_{p} = mg delta h

hookes law
Law stating that , for an object under tension , such as a wire or a spring , the extension is proportionAl to the applied force

Inertia
An objects resistance to acceleration ; for linear motion , this is the mass

instantaneous velocity
The rate of change of displacement , as measured over a very small time interval

Interference partern
A Series of maxima (points of constructive interference) and minima (Points of destructive interference) in a region where two or more waves overlap

Kinetic energy
The energy of a mass , m , moving at a velocity E_{k = 1/2mv}^{2}

Laser
A device that produces a highly monochromatic , coherent , non diverging light beam

Longitudinal wave
A wave that has oscillations parallel to the direction of travel of the wave

Newton
the S.I. unit of force ; 1 newton is the force that will Accelerate the mass of 1 kg at 1ms^{2}

Node
A poInt on a standing wave at which the amplitide is zero

optical fibre
A think strand of glass or plastic which carries light signals

Overtone
A vibration with a frequency that is a multiple of the fundamental frequency

Parallelogram law
A method for finding the resultant force of two vectors

path difference
The difference in the distance travelled by two waves ; commonly expressed as the number of wavelengths

phase difference
The difference in phase (the position in the cycle) of two waves , expressed in degrees or radians

In phase
Two waves are in phase if they are at the sAme point in their cycle at the same time

plastic behaviour
When a material if permanently deformed , even after the applied force is removed

Polarised
A transverse wave that is constrained to vibrate in one direction only is said to be polarised

Power
The rate at which energy is transferred or the rate at which work is done , measured in joules per second , or watts , W ,

principle of conservation of energy
law stating that the total energy of a closed system is constant

principle of moments
law stating that if an object is in equilibrium , the sum of the clockwise moments about any point must equal the sum of the anticlockwise moments about that point

principle of superposition
law stating that when two similar waves overlap , the total disturbance caused is the vector sum of the individual disturbances

progressive wave
a wave that transfer energy in the direction of the wave travel

rarefaction
a region of lower pressure or density in a longitudinal wave

refraction
the change in direction of a wave as it crosses a boundary between two mediums in which its speed differs

refractive index (absolute refractive index) (n)
property of an optical material equal to the ratio : speed opt light in a vacuum / speed of light in the material

relative refractive index n_{2}
the relative refractive index of material 2 relative to material 1 (n_{2}) is the ratio of : speed of light in medium 1 / speed of light in medium 2

resolution or resolving
the splitting up of a vector into components , usually perpendicular

resultant
the sum of two or more vectors such as forces

scalar
a physical quantity that is fully specified by its magnitude (size) ; it has no direction associated with it

snells law
law of refraction connecting the angle of incidence and angle of refraction with the absolute refractive indices of the materials either side of the boundary : n_{1}sinθ_{1} : n_{2}sinθ_{2}

spectrometer
a device that uses a diffraction grating to produce spectra or to measure the wavelength of monochromatic light

spectrum
the distribution of wavelengths in a light source

spring constant k
the force needed to stretch a spring by unit extension k = force/extension unit Nm^{1} its usually a measure of the stiffness of a spring

stationary or standing wave
a wave that doesn't transfer energy in the direction of wave travel ; it has stationary points called nodes

stiffens
the resistance to extension of a material under tension

strain or tensile strain ε
 the fractional increase in length of a wire , l , under tension
 ε = Δl/l
 it has no unit

strength
a measure of the force (stress) needed to cause fracture of a material

stress or tensile stress σ
 the force per unit cross sectional area
 σ = F/A

tensile force
a force acting to cause extension

tension
an object in tension is under the influence of of forces which tend to extend it

terminal velocity
the steady velocity reached by a falling object when the drag is equal to the weight

torque
 the rotational equivalent of a force
 torque produces rotational acceleration
 unit Nm

[total internal reflection
the complete reflection of a light ray at the boundary of two media , when the ray is in the medium with a lower speed of light

transverse wave
a wave that has oscillations perpendicular to the direction of wave travel

ultimate tensile stress or breaking stress
the maximum stress (force per unit area) that a material can withstand before it breaks

upthrust
the upward force on an object that is submerged in a fluid ; it is equal to the weight of the fluid displaced

vector
a physical quantity that is specified by its magnitude and direction

velocity
the rate of change of displacement ; velocity = change in displacement/time ; unit ms^{1}

watt
unit of power equal to the rat elf energy transfer of 1 joule per second

wavelength
the distance between consecutive points on a wave that have identical motion

work
work done = force x distance moved in the direction of the force

yield point
the minimum stress at which plastic deformation occurs

young modulus
the stiffness constant of a material , defined by the ratio : tensile stress/tensile strain

zero orde maximum
the central point at which the wave passing through a diffraction grating interfere constructively ; waves from adjacent slits have zero path difference and so all waves arrive in phase

physical quantities can be classified into two groups
scalars or vectors

give an example of a scalar quantity

scalar quantities must have
a magnitude but no direction associated with them

give an example of a vector quantity

a vector quantity is only fully specified when
the magnitude and direction is given

draw a table to show examples of scalar and vector quantities met in this unit
x

a vector quantity has
magnitude and direction whereas a scalar quantity only has magnitude

vector quantities are often identified by the use of
bold type

when two vectors are added
we need to take account their direction as well as their magnitude

two vectors can be added by
drawing a scale diagram showing the effect of one vector followed by the other

the sum of a number of vectors is known as the
resultant

the resultant is
the single vector that has the same effect as the combination of the other vectors

it is vital to take into account the relative direction of vectors when
adding them together , for example the resultant of two 5N forces could be anything from 0 to 10N depending on their directions

the resultant of two vectors can be also be found by the
parallelogram law . a parallelogram is constructed using the two vectors as adjacent sides . the resultant is the diagonal of the parallelogram

if the vector diagram is drawn to scale , the resultant vector can be found by
direct measurement from the diagram

for two vectors at right angles , the magnitude of the resultant can be found from
calculation by using pythag

subtracting a vector quantity can be though of as
adding a negative vector . the vector which is to be subtracted is reversed in direction . this reversed , or negative , vector is then to be added in the usual way

a single vector can be replaced by a combination of two of more vectors that would have the same effect this is known as
resolving a vector into its components and can be found as the reverse of finding the resultant . the components of a vector could be at any angle but it is often useful to use two components that are at right angles to each other . this might be to find the horizontal and vertical components of a force or a velocity

remember that the vector you are resolving is always the
hypotenuse of a triangle . the components will always be smaller than the original vector

it is often important to be able to identify and add together all the forces that are acting on an object . the size and direction of the resultant will
determine what happens to the object

everyday objects are subjected to a variety of forces such as
 weight
 contact forces
 friction
 tension
 air resistance
 buoyancy

all of those forces are
electromagnetic in origin except for weight . they arise because of the attraction or repulsion of the charges in atoms

the weight is the
force that acts on mass due to the gravitational attraction the earth

the gravitational field strength on the earth is
 9.81 Nkg^{1}
 this means that every kilogram of mass is attracted towards the earth with an attraction of 9.81 N

the weight of an object in newtons is given by
 weight (N) = mass (kg) 8 gravitational field strength (Nkg^{1})
 w=mg

the goal weight of a real object is
the sum of the gravitational attractions acting on every particle in the object . the resultant of these forces is the weight of the object which can be treated as a single force acting at one point in the object , this is known as the centre of gravity

whenever two solid surfaces touch they
exert a contact force on each other . this force is known as the reaction . it is the contact force between the floor and your feet that stops gravity pulling your feet through the ground . the resultant contact force between two surfaces could be at any angle

we usually split the contact force into two components
 the normal contact force acting perpendicularly to the two surfaces
 the frictional force acting parallel to the surfaces

a frictional force acts
between two surfaces whenever there is a relative motion between them , or when an external force is trying to slide past each other

an object is said to be in tension when
a force is acting to stretch the object . elastic materials , like ropes or metal cables resist this stretching and exert a force on the bodies trying to stretch them

ay object that is moving through a fluid is subject to
a resistive force or drag . any object moving through the atmosphere has to push the air out of the way , this gives rise to the drag force that acts to oppose relative motion between the object and the fluid

the size of the air resistance acting on an object depends on
the area of the object and the density of the air . the air resistance also increases as the relative speed between the object and the air increases . so as you go faster the force trying to stop you increases

buoyancy  any objects that are partly or fully submerged in a fluid like a boat floating on water or a hot air balloon floating in the atmosphere are subject to
an upthrust from the surrounding fluid

free body diagrams  the forces acting on a real object may be ver complex . a free body diagram is an attempt to
model the situation so that we can analyse the effect of the forces . the free body diagram is used to show all external forces that are acting on an object . since forces are vector quantities they are represented by arrows , drawn to scale and acting in the correct direction

