Physics XI - Chapter 15: Waves
Chapter-wise Multiple Choice Questions with Instant Feedback
Quick Revision Box: Waves
- Wave: A disturbance that propagates through space and time, transferring energy without a net movement of matter.
- Transverse Wave: Particle displacement is perpendicular to wave direction. E.g., Light, waves on a string.
- Longitudinal Wave: Particle displacement is parallel to wave direction. E.g., Sound waves.
- Crest & Trough: Maximum upward and downward displacements in a transverse wave.
- Compression & Rarefaction: Regions of high and low pressure in a longitudinal wave.
- Wavelength (λ): Distance between two successive crests/compressions. SI unit: meter (m).
- Time Period (T): Time taken for one complete wave to pass a point. Frequency (ν) = 1/T.
- Wave Velocity (v): Speed at which the wave propagates. v = νλ.
- Wave Equation: y(x,t) = a sin(ωt - kx + φ) represents a progressive wave.
- Angular Frequency (ω): ω = 2πν = 2π/T.
- Wave Number (k): k = 2π/λ. Represents spatial frequency.
- Speed of Sound: In a medium, v = √(B/ρ) for liquids/solids, and v = √(γP/ρ) for gases.
- Principle of Superposition: When two waves meet, the resultant displacement is the vector sum of individual displacements.
- Reflection: A wave bouncing back into the same medium upon striking a surface. Laws: i = r.
- Refraction: Bending of a wave when it enters a medium with different speed. Governed by Snell's Law.
- Interference: The combination of two coherent waves leading to a stable pattern of reinforcement or cancellation.
- Constructive Interference: Occurs when path difference = nλ. Results in maximum amplitude.
- Destructive Interference: Occurs when path difference = (n + ½)λ. Results in minimum amplitude.
- Beats: The periodic variation in intensity due to the superposition of two waves of slightly different frequencies. Beat Frequency = |ν₁ - ν₂|.
- Doppler Effect: Apparent change in frequency due to relative motion between source and observer.
- Standing Waves: Formed by the superposition of two identical waves traveling in opposite directions. Characterized by nodes and antinodes.
Basic Level Questions
Chapter Summary
This chapter immersed us in the world of Waves, the dynamic carriers of energy that shape our experience of sound, light, and music. We started by classifying waves into transverse and longitudinal, understanding their fundamental characteristics like wavelength, frequency, amplitude, and wave velocity, all connected by the vital equation v = νλ.
We then explored the behavior of waves when they interact. The Principle of Superposition is the golden rule here, explaining fascinating phenomena like interference, where waves combine to create patterns of loud and soft sounds, and beats, that wavering sound we hear when two tuning forks are slightly out of tune. We also studied how waves bounce (reflection) and bend (refraction) at the boundaries between different media.
The chapter introduced two key concepts for your exams: the Doppler Effect, which explains why a siren's pitch changes as it passes by, and standing waves, the stationary patterns formed in musical instruments that define their notes. This chapter provides the essential foundation for understanding how energy and information travel through the world around us.