Waves phys

What name can be given to transverse waves whose oscillations have been restricted to a single plane ?

PLANE - Polarised

To keep the small angle approximation, What must D be much larger than in the diffraction grating equation ?

D >> s

D >> w

What can be used to polarise light ?

Polaroid filter

What plane must a receiver be aligned in?

The same plane as the transmitter

Why must a receiver be aligned in the same plane as the transmitter?

The transmitter produces plane-polarised waves,

Thus the electric-field oscillations are only occurring in a single plane,

So the signal can only be received (fully) if the receiver antenna is also in this plane.

Describe the energy of a stationary wave?

Transferred between energy stores internally,

No net energy transfer (ideally) of whole system

Why are signals safer in optical fibres than in copper cables?

Any damage to the core of the fibre results in light scattering thus signal is lost,

Whereas the signal can be "tapped off" by determining voltage in copper cables

With transmitters and receivers, when will the receiver detect the greatest and weakest signal?

Greatest when in same plane as waves,

Weakest when in a plane 90 degrees to that of the waves

Why are optical fibres more efficient than copper cables?

No energy loss due to heating

Explain the impacts of pulse broadening in optical fibres

Signals overlap, which reduces signal clarity and limits bit rate.

Explain the impacts of light escaping in optical fibres

Reduced amplitude/intensity /attenuation of signal,

Requires signal repeaters along fibre to correct signal.

Why is the cladding needed in optical fibres?

Prevent cross talk between fibres,

protect the fibre from scratches,

ensure TIR

How has knowledge of EMR changed overtime?

Young : showed light can behave as a wave,

Polarisation : shows light is a transverse wave

Einstein's photoelectric effect : showed that light can behave as a particle

Data was validated and peer reviewed,

Now : accept the wave-particle nature of EMR

What is true if constructive interference occurs?

Waves meet in phase

phase difference = 0 / 360 degrees

path difference = n lambda

Define “Progressive waves”

Waves that transfer energy, not matter, from one point to another

Define “Phase”

A measure of the stage of oscillation of a point in its wave cycle, relative to the start of its cycle, measured in degrees or radians

What is the displacement at a Node on a stationary wave?

There is ZERO displacement

Points separated by an odd number of nodes on a stationary wave are …

out of phase / in antiphase

Which plane are we referring to when we talk of “Plane-polarised waves” ?

The plane that contains both the oscillations of the electric field and the direction of energy transfer

How will the metal bars in a metal grill be arranged to ensure TRANSMISSION

They must be perpendicular to the plane of polarisation of the wave

Why is the wave absorbed if the metal bars in the metal grill are parallel to the plane of polarisation of the wave?

The metal bars are the absorption axis : the electric field causes electrons in the metal to oscillate, creating a current. The wave transfers its energy

Why are microwaves often just accepted as being plane-polarised?

Artificially produced microwaves (from transmitters) will be plane-polarised

What are possible applications of a diffraction grating ? (3)

1) determining the unknown wavelength of light

2) determining the chemical composition of unknown substances

3) observing light from distant galaxies

What can be said about a wave when it reaches any boundary

It must, at least, PARTIALLY reflect

True or False: minima are well-defined if white light has been used in Young’s double slit / single slit experiment ?

False : fringes overlap so minima are not well-defined

Give two reasons as to why the fringe intensity decreases if slit width decreases

1) less light passes through the slits

2) angle of diffraction is greater so light is spread over a greater area

Why do we care about s (the slit separation) in diffraction experiments?

s must be small enough that the diffracted waves can interfere

Why do we care about the slit width in diffraction experiments?

s must be small enough that the wave actually diffracts

What is the relationship between wavelength and wavespeed in refraction?

They are directly proportional

What remains constant in refraction?

frequency

What is a phase difference of π/2 in degrees?

90°

When does the comparability between λ and slit width matter?

When discussing SINGLE SLIT diffraction

Why does θ for n=1 decrease if λ decreases when using a diffraction grating?

Sin θ = λ / d

d is constant

Thus sin θ is directly proportional to λ

Thus θ is directly proportional to λ