This question is about waves - Edexcel - GCSE Physics - Question 2 - 2022 - Paper 1

To calculate the wavelength, we can use the formula for wave speed:

$v = f \times \lambda$

Where:

• $v$ is the wave speed
• $f$ is the frequency
• $\lambda$ is the wavelength.

First, we need to find the number of wavelengths between P and Q. Since the distance between P and Q is 42 cm and there are 6 crests (which indicates 6 wavelengths), the wavelength can be calculated as follows:

$\lambda = \frac{\text{Distance}}{\text{Number of wavelengths}} = \frac{42 \text{ cm}}{6} = 7 \text{ cm}$

Thus, the wavelength of the water wave in Figure 3 is 7 cm.