Definitions

1. Amplitude

• Definition: The maximum displacement of a wave from its equilibrium (rest) position.
• Explanation: This is the height of the wave peak (or depth of the trough) from the central axis. In sound waves, amplitude correlates with loudness, while in light waves, it's related to brightness.

2. Antinode

• Definition: A point in a stationary wave where the displacement is maximum.
• Explanation: Found at positions where two waves constructively interfere, leading to a peak in wave amplitude. In a stretched string, antinodes appear as points that vibrate the most.

3. Cladding (Optical Fibres)

• Definition: A protective layer around an optical fibre, which enhances the fibre's strength and prevents signal loss between adjacent fibres.
• Explanation: Cladding keeps light confined within the core by total internal reflection, which is crucial for long-distance data transmission in fibre optics.

4. Coherence

• Definition: Waves are coherent if they have the same frequency, wavelength, and maintain a constant phase difference.
• Explanation: Coherent waves are necessary for stable interference patterns. Lasers produce coherent light, making them ideal for applications like holography.

5. Diffraction Grating

• Definition: A tool with many parallel slits that disperses light into its component colours through diffraction.
• Explanation: Diffraction gratings are used in spectrometers to analyse light spectra, helping in atomic and molecular analysis.

6. Diffraction

• Definition: The spreading of waves when they encounter a gap or obstacle.

7. Electromagnetic Waves

• Definition: Waves made up of electric and magnetic fields oscillating perpendicular to each other.

8. Frequency ($f$)

• Definition: The number of wave cycles that pass a point per second, measured in hertz (Hz).
• Calculation: Frequency is the inverse of the period $f = 1/T$. High-frequency waves have shorter wavelengths.

9. Fringe Spacing

• Definition: The distance between adjacent bright or dark fringes in an interference pattern.

10. Interference

• Definition: The process where two or more waves overlap, resulting in a new wave pattern.
• Types: Constructive (amplitudes add up) and destructive (amplitudes cancel out). For example, noise-cancelling headphones use destructive interference.

11. Laser

• Definition: A light source that emits coherent, monochromatic, and collimated light.
• Applications: Used in surgeries, barcode scanners, and communications due to their precision and intensity.

12. Longitudinal Waves

• Definition: Waves where particle oscillations are parallel to the wave's direction.

13. Material Dispersion

• Definition: The spreading of light pulses in an optical fibre due to different wavelengths travelling at different speeds.
• Solution: Using monochromatic light sources like lasers reduces dispersion effects, crucial for high-speed data transfer.

14. Modal Dispersion

• Definition: Dispersion occurring in multimode optical fibres where different paths (modes) cause light rays to arrive at different times.
• Effect: It causes pulse broadening, limiting the fibre's data transmission rate.

15. Node

• Definition: A point in a stationary wave with zero displacement.
• Explanation: Nodes occur where destructive interference consistently cancels out the wave, resulting in no motion at these points.

16. Optical Fibre

• Definition: A thin glass or plastic fibre for transmitting light signals.
• Components: Core (carries light), cladding (protects core and reduces signal loss). Used in telecommunications and medical imaging.

17. Path Difference

• Definition: The difference in the distance travelled by two waves arriving at a point.
• Usage: Important in interference calculations, especially for double-slit experiments, where it affects fringe positions.

18. Phase Difference

• Definition: The difference in phase between two points on a wave or between two waves.
• Explanation: Measured in degrees or radians. If two waves are in phase, they add constructively; if out of phase by $180^\circ$, they cancel each other.

19. Polarisation

• Definition: Restricting a transverse wave to vibrate in a single plane.

20. Pulse Broadening

• Definition: Widening of a light pulse as it travels through an optical fibre, due to dispersion effects.
• Solution: Single-mode fibres reduce this effect, enabling higher data transmission rates.

21. Refractive Index ($n$)

• Definition: A measure of how much a material slows down light, defined by $n = \frac{c}{v}$.

22. Snell's Law

• Formula: $n_1 \sin \theta_1 = n_2 \sin \theta_2$.
• Application: This law describes how light bends when moving between media of different refractive indices, such as air to water.

23. Stationary Wave

• Definition: A wave that appears to stand still, created by the interference of two waves moving in opposite directions.

24. Total Internal Reflection

• Definition: Complete reflection of light inside a denser medium when the angle of incidence exceeds the critical angle.
• Application: This principle is crucial for optical fibres, which use it to keep light confined within the core.

25. Transverse Wave

• Definition: A wave where oscillations are perpendicular to the direction of energy transfer.

26. Wavelength $(\lambda)$

• Definition: The distance between two consecutive identical points on a wave, such as crest to crest.
• Relationship: Wavelength is inversely proportional to frequency for a given wave speed.

27. Young's Double-Slit Experiment

• Description: An experiment showing interference by passing light through two slits, producing bright and dark fringes on a screen.
• Significance: Provides evidence of light's wave nature. The fringe spacing formula, $w = \frac{\lambda D}{s}$, helps calculate the wavelength of light.