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 and can propagate through a vacuum.

Transverse waves have particle motion that is perpendicular to the direction of wave propagation, while longitudinal waves have particle motion that is parallel to the direction of wave propagation.

Diagram: A labelled diagram showing:

• A transverse wave with crests and troughs, illustrating the perpendicular motion.
• A longitudinal wave with compressions and rarefactions, illustrating the parallel motion.

To calculate the speed of the radio waves, we use the formula:
$v = f imes ext{wavelength}$
Where:

• Frequency, $f = 107 imes 10^6$ Hz
• Wavelength = 2.804 m

Substituting the values: $v = (107 imes 10^6) imes 2.804$ $v = 3.00 imes 10^8 ext{ m/s}$

An example of sound wave reflection is an echo. When sound produced in an open area encounters a large surface, such as a wall or a mountain, it reflects back, creating an echo that can be heard after a short delay.

Using Snell's law, which states that:
$n = \frac{\sin(i)}{\sin(r)}$
Where:

• $i = 23^{\circ}$ (angle of incidence)
• $r = 15^{\circ}$ (angle of refraction)

Calculating: $n = \frac{\sin(23^{\circ})}{\sin(15^{\circ})} \approx 1.51$

To illustrate diffraction:

• Draw wavefronts spreading out from the slit in a smooth curve, maintaining an appropriate distance between the wavefronts, indicating the change in direction as the waves pass through the gap.

An experiment to demonstrate sound interference can be done using two speakers:

Method:

1. Position two speakers in phase, emitting the same frequency sound waves.
2. Measure the sound intensity at varying points in the space around the speakers.
3. Observe alternating areas of increased sound intensity (constructive interference) and decreased sound intensity (destructive interference).

This illustrates how sound waves interact with each other.

Polarisation is the process by which oscillations of a transverse wave, such as light, are restricted to a single direction.

Diagram:

1. Draw a transverse wave with vibrations in multiple planes.
2. Show a polarised wave with vibrations limited to one plane only.

This distinction illustrates how light can be polarised while sound cannot, since sound waves are longitudinal and do not support such orientation.