5. (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 waves have shorter wavelengths and cannot pass through obstacles effectively. Hence, when an infrared remote control is used from behind an armchair, it may not reach the television due to obstruction. In contrast, radio waves have longer wavelengths and can penetrate through solid objects more efficiently, making a radio wave remote control always function regardless of obstructions.

To find the wavelength, measure the distance between two consecutive crests or troughs on Figure 4. Assume the measured value is approximately 10 cm.

The cork floats on the water while moving in a circular motion. As the wave travels, the cork rises and falls vertically without moving forward in the direction of the wave. It moves upwards as the wave crest approaches, and downwards as it moves to the trough, thereby oscillating vertically.

Wave speed can be calculated using the formula:

$ext{wave speed} = ext{wavelength} imes ext{frequency}$

Here, the wavelength is 0.25 m and the frequency is 1.5 Hz:

$ext{wave speed} = 0.25 imes 1.5 = 0.375 ext{ m/s}$.