The graph shows the variation with the time of the displacement of a particle in a medium when a wave of intensity I travel through the medium. The Intensity of the wave is halved. Which graph now represents the variation of displacement with time? (The scale on all graphs is the same.)

 

Travelling waves of wavelength $32 \mathrm{cm}$ are created in a closed-open pipe $\mathrm{X}$ of length $40 \mathrm{cm}$ and an open-open pipe $\mathrm{Y}$ of length $50 \mathrm{cm}$. In which pipe or pipes will a standing wave be formed?

Partially polarised light is a combination of completely unpolarised light and light that is polarised. Partially polarised light is transmitted through a polariser. As the polariser is rotated by $360°$, the ratio of the maximum to the minimum transmitted intensity is $7$.

Determine the fraction of the beam's intensity that is due to the polarised light.