The Shape That Travels

What this book is about

Somewhere in your physics course a chapter appears called *Waves*, and it arrives carrying a great deal of luggage: y = A sin(ωt − kx), nodes and antinodes, Newton's formula and Laplace's correction, closed pipes and open pipes, beats, Doppler, fringe width. Most students learn to survive it. Very few come out of it feeling that they understood what a wave actually is.

This book takes the whole thing apart and rebuilds it from the bottom. It assumes you can read a graph and have met sine and cosine, and it assumes nothing else. Every formula in it is built on the page where it first appears, out of things you already have. Nothing arrives by decree.

The subject matter follows the standard Higher Secondary syllabus — periodic motion and waves from the first paper, physical optics from the second — but it is not arranged the way a syllabus is arranged. It is arranged the way the ideas actually depend on one another, which is not the same thing, and is a good deal easier to remember.

What is inside

• The back-and-forth: the one rule that makes a sine, the shadow of a circle, why the

period ignores the amplitude, and g measured in your own courtyard

• The disturbance that travels: what actually moves, the two graphs everyone confuses, and

where v = fλ comes from

• Sound: Newton's answer and its 16 per cent error, the one word Laplace changed, and what

loud, high and sweet really mean

• When waves meet — superposition, interference, standing waves, pipes, resonance and beats
• Doppler, the redshift of galaxies, ultrasound, sonar and echo
• Light is a wave too: a 150-year argument, Young's two slits in 1801, fringes,

diffraction, Poisson's spot, polarisation, and the whole electromagnetic family

• Two experiments to do at home, everything on one sheet, eighteen worked exercises, a

Bangla–English glossary and a quiz