Figure 6 shows a large tank of water - Edexcel - GCSE Physics Combined Science - Question 4 - 2020 - Paper 1

To find the wavelength, we divide the total distance between points L and M (32 m) by the number of wavelengths. Since the pattern shows 10 wavelengths in that span, we calculate:

$ext{wavelength} = \frac{32 \text{ m}}{10} = 3.2 \text{ m}$

The frequency can be calculated using the formula:

$\text{frequency} = \frac{\text{Number of peaks}}{\text{Time}}$

Substituting the values:

$\text{frequency} = \frac{12 \text{ peaks}}{15 \text{ s}} = 0.8 \text{ Hz}$

Arrows should be drawn to indicate that the rock at R moves back and forth in the same direction as the wave propagation, demonstrating the longitudinal nature of the seismic wave.

Using the formula:

$\text{wavelength} = \frac{\text{wave speed}}{\text{frequency}}$

Substituting the values:

$\text{wavelength} = \frac{7 \text{ km/s} \times 1000 ext{ m/km}}{12 \text{ Hz}} = \frac{7000}{12} \approx 583.33 ext{ m}$

The wavelength is approximately 580 m.

Counting waves for the seismic wave would not be suitable because seismic waves cannot be seen upon arrival. A technician would need an alternative means of detection. Additionally, counting waves can be challenging as a person may count too quickly or lose track of the waves.