(a) Which colour of visible light has the longest wavelength? A blue B green C red D yellow (b) Some television remote controls use infrared radiation and other remote controls use radio waves - Edexcel - GCSE Physics Combined Science - Question 5 - 2019 - Paper 1

Infrared remote controls operate using infrared radiation, which has a shorter wavelength and can be blocked by obstacles like furniture. This means that if the remote is obstructed by an armchair, the signal may not reach the television. In contrast, radio waves have longer wavelengths that can diffract around obstacles, allowing them to effectively communicate regardless of barriers, thus ensuring the radio wave remote control will work even when blocked.

To find the wavelength, measure the distance between two consecutive crests (or troughs) of the wave represented in Figure 4. Assume the measurement shows that the distance between two crests is 10 cm. Therefore, the wavelength is 10 cm.

The cork moves in a circular motion as the wave passes beneath it. While the wave travels horizontally from left to right, the cork rises and falls vertically, oscillating up and down, maintaining its position horizontally as it moves with the crest and trough of the wave.

Wave speed can be calculated using the formula:

$ext{Wave speed} = ext{Wavelength} imes ext{Frequency}$

Substituting in our values:

$ext{Wave speed} = 0.25 ext{ m} imes 1.5 ext{ Hz} = 0.375 ext{ m/s}$

Thus, the wave speed is 0.375 m/s.