Global challenges Study Guide

Transformers are electrical devices that change the potential difference (voltage) of an alternating current (AC) supply. They are crucial in the efficient transmission of electrical power from power stations to homes and industries. There are two main types: step-up transformers and step-down transformers. Step-up transformers increase the potential difference and decrease the current for efficient transmission over long distances. This is because transmitting power at a high potential difference and low current significantly reduces energy loss due to heating in the transmission cables. Power loss is proportional to the square of the current (P=I²R), so reducing current has a large impact. Once the power reaches towns and cities, step-down transformers are used to decrease the potential difference to safer, more usable levels for domestic and industrial applications. This staged approach ensures that power is transmitted efficiently and delivered safely.

Sound waves and seismic waves are types of waves that can travel through different materials at different speeds and with varying degrees of absorption and reflection. This behaviour is fundamental to how scientists explore hidden structures, such as the Earth's core or objects beneath deep water. When waves encounter a boundary between two different materials, some of their energy is reflected, and some is transmitted and refracted (changes direction and potentially speed). The amount of reflection and transmission depends on the properties of the materials, such as their density and elasticity. For instance, waves generally travel faster through denser, more rigid materials. Liquids, being less rigid than solids, typically transmit shear (S) waves poorly or not at all, while compressional (P) waves can still pass through, albeit at a reduced speed compared to solids. By transmitting waves and then detecting the reflected or transmitted waves, scientists can infer the presence, depth, and composition of hidden structures. For example, in seismic surveys for Earth's interior, earthquakes generate P and S waves. The analysis of how these waves travel through the Earth, reflecting off boundaries and changing speed in different layers, allows geophysicists to map the Earth's internal structure, including the solid inner core and liquid outer core. Similarly, sonar systems use sound waves in water to detect objects or map the seabed by measuring the time taken for echoes to return and the strength of those echoes. The differences in wave speed, absorption, and reflection provide valuable qualitative information about the nature of the materials encountered by the waves. Increased absorption often indicates a less dense or more attenuating medium, while stronger reflections suggest a significant change in material properties.