A wave can be described as a travelling disturbance that transports energy from one point to another - Leaving Cert Physics - Question 8 - 2021

Electromagnetic waves do not require a medium to travel. They can propagate through a vacuum.

To find the speed of radio waves, use the formula:

$v = f imes au$

where:

• $f = 107 \text{ MHz} = 107 \times 10^6 \text{ Hz}$
• $\tau = 2.804 \text{ m}$

So,

$v = (107 \times 10^6) \times 2.804 \approx 3 \times 10^8 \text{ m/s}$

An example of sound wave reflection is an echo. When a sound is produced and reflected off a distant surface, it returns to the listener, causing the perception of the same sound after a delay.

To calculate the refractive index ($n$), use Snell's Law:

$n = \frac{\sin(i)}{\sin(r)}$

where:

• $i = 23°$ (angle of incidence)
• $r = 15°$ (angle of refraction)

Calculating:

$n = \frac{\sin(23°)}{\sin(15°)} \approx \frac{0.3907}{0.2588} \approx 1.51$

To complete the diagram, illustrate the wave fronts spreading out as they move past the gap. The wave fronts should bend and fan out from the slit.

To demonstrate sound interference:

1. Apparatus: Use two speakers and a sound level meter.
2. Procedure: Place the speakers parallel to each other at a distance. Play the same frequency from both speakers.
3. Observation: Move a microphone or sound level meter around the area between the speakers and note variations in sound intensity due to constructive and destructive interference.
4. Conclusion: The varying sound levels indicate interference patterns.

Polarisation of light waves occurs when waves vibrate in a single plane. An example can be illustrated using a diagram that shows light passing through a polarising filter, with arrows indicating the direction of vibration. In contrast, sound waves vibrate in all directions, making them inherently unpolarised.