Zed Physics Lecture: Wave Section of A-Level Physics

Introduction

• Revision of the wave section from the A-Level Physics syllabus.
• Following the OCR physics A specification; applicable to all exam boards.

Types of Waves

Progressive Waves

• Transfer energy from one place to another.
• Can be split into:
  • Transverse Waves: Particles oscillate perpendicular to direction of wave propagation. Examples: water waves, electromagnetic (EM) waves.
  • Longitudinal Waves: Particles oscillate parallel to direction of wave propagation. Examples: sound waves, P-waves in earthquakes.

Wave Properties

• Displacement: Distance from a wave point to equilibrium.
• Amplitude: Maximum displacement from equilibrium.
• Wavelength: Minimum distance between two points in phase.
• Time Period: Time for one complete oscillation.
• Frequency: Number of cycles per unit time (measured in Hertz).

Wave Speed

• Defined as the distance wave travels per unit time.
• Equations:
  • Speed (v = \frac{\text{distance}}{\text{time}})
  • For one cycle, distance = wavelength and time = time period.
  • (v = f \lambda) where (v) is speed, (f) is frequency, and (\lambda) is wavelength.

Phase Difference

• Describes how out of sync two wave points are.
• Equation: (\text{Phase difference} = \frac{x}{\lambda} \times 360^\circ)
• Example: For waves with peaks separated by 60 cm and wavelength 80 cm, phase difference = 270°.
• Rule: 180° phase difference means a peak meets a trough (half wavelength difference).

Oscilloscopes

• Horizontal = time interval, Vertical = voltage.
• Example settings: 1 ms/cm and 2 V/cm.
  • Time period = 4 ms, Amplitude = 2 V, Frequency = 250 Hz.

Wave Behaviors

Reflection

• Wave changes direction at boundary, remains in the original boundary.
• Angle of incidence = angle of reflection.

Refraction

• Wave changes direction and speed between media.
• Frequency constant, but speed and wavelength change.

Diffraction

• Spreading of a wave through a gap/around an obstacle.
• Gap size similar to wavelength.

Intensity

• Defined as power transmitted per unit area (W/m²).
• Intensity (I = \frac{P}{A}) where (P) is power and (A) is area.
• Intensity decreases with distance from a point source.

Intensity and Amplitude

• Intensity (\propto \text{Amplitude}^2).
• Doubling amplitude quadruples intensity.

Electromagnetic Waves (EM)

• Travel through a vacuum at speed of light ((3.0 \times 10^8) m/s).
• Types include radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.

Polarization

• Plane polarized if fields oscillate in one plane.
• Longitudinal waves cannot be polarized.
• Polarizing filters block certain light components.

Refractive Index

• Ratio of speed of light in vacuum to speed in a substance ((n = \frac{c}{v})).
• Example: Refractive index of diamond is 2.4, speed of light in diamond = 1.25 (\times 10^8) m/s.

Total Internal Reflection

• Occurs when light travels from a medium with a higher to lower refractive index.
• Critical angle is the minimum angle of incidence for total internal reflection.
• Snell's Law: (n_1 \sin \theta_1 = n_2 \sin \theta_2).

Conclusion

• Further topics such as superposition and stationary waves are covered in separate videos.
• Good luck in exams!