Nature of Waves

Question 1

Polarised Light

Answer 1

Vibration of transverse light waves in only one plane perpendicular to the direction of travel.

Question 2

Non-Polarised Light

Answer 2

Vibration of transverse light waves in numerous planes perpendicular to the direction of travel.

Question 3

Coherence

Answer 3

Waves that are in-phase and have equal frequency.

Question 4

Standing Wave

Answer 4

Interference caused by the superposition of two or more waves travelling in opposite directions with equal amplitude, frequency and wavelength. System of nodes and antinodes.

Question 5

Transverse Wave

Answer 5

Wave which propagates energy through a medium, particles oscillate perpendicular to the direction of travel.

Question 6

Longitudinal Wave

Answer 6

Wave which propagates energy through a medium, particles oscillate parallel with the direction of travel.

Question 7

Multimode Fibres

Answer 7

Large range of path lengths therefore times.
Pulses therefore take different paths and times, pulse broadening. This causes pulses to disperse and overlap, arriving out of order.

Question 8

Amplification

Answer 8

An incident photon causes stimulated emission of another in-phase and coherent photon, causing an excited electron to drop to a lower energy level. This occurs repeatedly as photons reflect back and forth, travelling across the amplification medium each time, intensifying the light as photons increase in number.

Question 9

Population Inversion

Answer 9

Achieved by pumping, there will be more excited electrons in the higher orbital than the lower, making stimulated emission more probable and absorption less probable.

Question 10

Path Diff.

Answer 10

At any fringe, path difference is n x lambda

Question 11

Check for Polarity

Answer 11

Place polarising filter in front of light source and a light sensor behind the filter. Rotate filter through 180 degrees.
If signal strength detected at sensor changes during rotation, light is polarised.

Question 12

Diffraction Grating

Answer 12

Sheet with an array of equally spaced slits, each of equal width.

Question 13

Grating > Young

Answer 13

Slits are spaced much closed in a diffraction grating than in Young’s model, causing the fringes to have more clarity and be further apart.

Question 14

Refraction

Answer 14

As waves pass from a lower to a higher refractive index medium, their velocity decreases, therefore decreasing their wavelength when in the 2nd medium. If the waves enter the 2nd medium at an angle, they bend towards the normal when passing between the two media.
[Reference diagram]

Question 15

Standing wave / Progressive wave

Answer 15

Different amplitude on every point, same amplitude everywhere
Wavelength is 2xinternodal distance, wavelength is distance between two crests/troughs
Particles between nodes in phase, not in phase.
Does not propagate energy, propagates energy

Particles oscillate in both

Question 16

Progressive wave

Answer 16

Particle oscillations through a medium across a distance that carries energy without transporting matter, where there is constant amplitude.

Question 17

Monomode Fibres

Answer 17

Smaller core than multimode fibres, therefore only allows one path light can take

Question 17

Slit Width Relation to Diffraction

Answer 17

If slit width&raquo_space; wavelength, the wave will pass undisturbed
As slit width gets closer to wavelength, diffraction will occur until the wave spreads across 180 degrees.

Question 18

Antiphase

Answer 18

Waves that are lambda/2 out of phase/phase diff. will arrive exactly out of phase and destructively interfere.

Question 19

Principle of Superposition

Answer 19

The resulting displacement of two or more interfering waves is the algebraic sum of the individual displacements of those interfering waves.

Question 20

Fibres

Answer 20

Light beams are internally reflected along the core and there is no loss due to large angles the light reflects off the sides to the normal