Question

If the ratio of final and initial intensities for 4% - solution of urea is 1/2 (length of beaker is 20 mm). Determine the ratio of intensities for 8%- solution of urea in the beaker of length l2 =30 mm.

Answer 1

The intensity decreases with the square of the beaker length:

$$\frac{I_f}{I_i}=\omega\frac{k}{d^2},\\\space\\ k=\frac{I_fd^2}{I_i\omega}.$$

For another beaker and solution:

$$\frac{I_f'}{I_i'}=\frac{\omega'}{\omega }\frac{I_fd^2}{I_id'^2}=\frac{4}{9}$$