A telecommunications company uses microwave signals to transmit data between a ground station and a geostationary satellite in orbit above the equator. The ...

(a) The type of electromagnetic wave used is microwaves. [1]

Microwaves are part of the electromagnetic spectrum and are specifically chosen for satellite communication because they can penetrate the Earth's atmosphere with minimal absorption and can be focused into tight beams by dish antennas.

(b) The satellite is at a height of 36 000 km above the Earth's surface. First, convert this to metres:

\( d = 36\,000 \text{ km} = 3.6 \times 10^7 \text{ m} \)

Using \( \text{speed} = \frac{\text{distance}}{\text{time}} \), rearranged to \( t = \frac{d}{v} \):

\( t = \frac{3.6 \times 10^7}{3.0 \times 10^8} \) [1]

\( t = 0.12 \text{ s} \) [1]

The signal takes just over a tenth of a second to travel from the ground to the satellite, which is a consequence of the enormous speed of electromagnetic waves.

(c) The signal must travel from station A up to the satellite (36 000 km) and then back down to station B (another 36 000 km). The minimum total distance is approximately:

\( 2 \times 36\,000 = 72\,000 \text{ km} \)

So the minimum delay is approximately \( 2 \times 0.12 = \mathbf{0.24 \text{ s}} \) [1]

This is the minimum because the actual path length may be slightly longer if the stations are not directly below the satellite.

(d) One other use of microwaves: cooking food (in a microwave oven). [1]

Other acceptable answers include mobile phone signals, radar, Bluetooth or Wi-Fi communication.

(e) Microwaves are used rather than radio waves because microwaves can pass through the Earth's atmosphere with less absorption and can be focused into narrow beams by dish antennas. [1]

Radio waves of longer wavelength would spread out more, making it harder to direct the signal precisely at the satellite, and some radio frequencies are absorbed or reflected by the ionosphere.

(f) High-intensity microwaves can cause internal heating of body tissue, which can lead to burns. [1]

This is the same principle used in microwave ovens: the microwaves cause water molecules to vibrate, generating heat.

(g) All electromagnetic waves travel at the same speed in a vacuum, which is \( 3.0 \times 10^8 \text{ m/s} \) (the speed of light). [1]

This is the one property that unites every member of the electromagnetic spectrum, from radio waves to gamma rays. Their frequencies and wavelengths differ, but their speed in a vacuum is identical.