Light travels as a wave of electromagnetic radiation - Leaving Cert Physics - Question 9 - 2020

To find the wavelength, we use the equation:

$\lambda = \frac{v}{f}$

where $\lambda$ is the wavelength, v is the speed of light ($3 \times 10^8$ m/s), and $f$ is the frequency ($5 \times 10^{14}$ Hz).

Substituting the values:

$\lambda = \frac{3 \times 10^8}{5 \times 10^{14}} = 6 \times 10^{-7} \text{ m}$

Thus, the wavelength of orange light is $6 \times 10^{-7}$ m.

One experiment to demonstrate that sound needs a medium involves using a bell jar. Place a bell inside the jar and connect it to a vacuum pump. Start with the bell ringing in normal air, which allows the sound to be heard. Next, slowly evacuate the jar. As the air is removed, the sound becomes fainter until it is inaudible, demonstrating that sound requires a medium (air) to travel.

Reflection refers to the bouncing back of waves when they encounter a surface that does not absorb the energy of the wave. For sound waves, this can be seen when you shout and hear your echo, as the sound waves bounce off a surface, such as a wall.

To demonstrate sound interference, you can use two speakers connected to the same audio source. Place the speakers at a fixed distance apart, and adjust their positions. When they are played simultaneously, changing the distance between them creates areas of constructive and destructive interference, which can be heard as variations in sound volume at different locations.

Polarisation occurs in transverse waves, where the oscillation direction can be restricted to a single plane. Since sound waves are longitudinal, characterized by oscillations in the same direction as wave propagation, they cannot be polarized.

To demonstrate the Doppler effect, set up a sound source (like a buzzer) on a cart that can move along a straight track. As the cart moves towards an observer, the sound frequency appears higher, and as it moves away, the frequency appears lower. Measure the frequency with a sound sensor at different distances to quantitatively analyze the shift in frequency.

One use of the Doppler effect is in radar and sonar systems, where it is employed to determine the speed and direction of moving objects by analyzing changes in the frequency of the waves reflected from them.