Global challenges Revision Notes

Non-renewable Energy Sources

Non-renewable energy sources are finite and cannot be replaced in a human timescale once used. They are formed over millions of years from the remains of ancient organisms. The main examples are fossil fuels: coal, oil, and natural gas. These are primarily used for generating electricity in power stations, heating buildings, and fuelling transport (petrol and diesel for cars, kerosene for jets). Nuclear fuel, such as uranium, is also non-renewable. It is used in nuclear power plants to heat water and produce steam, which then drives turbines to generate electricity. The key disadvantage of fossil fuels is their contribution to global warming due to carbon dioxide emissions. Nuclear power produces radioactive waste that needs careful, long-term storage.

Renewable Energy Sources

Renewable energy sources are naturally replenished, offering a sustainable alternative to non-renewable fuels. Solar power harnesses sunlight, either directly for heating water or via photovoltaic cells to generate electricity. Wind power uses wind turbines to convert kinetic energy into electricity. Hydroelectric power uses the gravitational potential energy of water stored behind dams. Geothermal energy taps into heat from the Earth's interior, often used for heating or electricity generation. Tidal power uses the movement of ocean tides to drive turbines. Biomass energy involves burning organic matter (like wood or crops) to produce heat or electricity. These sources generally have a lower carbon footprint than fossil fuels, but their availability can be intermittent (e.g., solar and wind) or geographically limited (e.g., geothermal and hydroelectric).

Uses of Different Energy Sources

Different energy sources are best suited for various applications. Fossil fuels have traditionally been the backbone of global energy supply due to their high energy density and ease of transport. They power the majority of our vehicles, heat homes, and generate a significant portion of our electricity. Nuclear power provides a reliable, large-scale supply of electricity without direct greenhouse gas emissions, though it has waste disposal challenges. Renewable sources are increasingly being integrated into electricity grids to reduce reliance on fossil fuels. Solar panels provide electricity for homes and businesses, and wind farms contribute significantly to national grids. Hydroelectric power is a major source of clean electricity in many regions. Geothermal energy can directly heat buildings or generate electricity. Tidal and biomass are more niche but contribute to diversify the energy mix.

Distinguishing Renewable and Non-renewable

The fundamental difference between renewable and non-renewable energy sources lies in their rate of replenishment. Non-renewable sources, like coal, oil, natural gas, and uranium, exist in fixed amounts or are formed too slowly to be considered sustainable on a human timescale. Once consumed, they are gone for good, or take millions of years to reform. Renewable sources, such as solar, wind, hydro, geothermal, and biomass, are continuously regenerated by natural processes. Their supply is virtually limitless, though their availability can vary seasonally or daily. This distinction is critical for long-term energy planning and environmental sustainability. Shifting towards renewable sources is a key strategy for mitigating climate change and ensuring future energy security.

Components of Stopping Distance

Stopping distance is the total distance a vehicle travels from when a driver first identifies a hazard until the vehicle comes to a complete stop. It is comprised of two distinct parts: thinking distance and braking distance. Thinking distance is the distance covered while the driver reacts and moves to apply the brakes. Braking distance is the distance covered from the moment the brakes are applied until the vehicle stops. Both components are critical for understanding road safety and preventing accidents.

Factors Affecting Thinking Distance

Thinking distance is affected by two primary factors: the vehicle's speed and the driver's reaction time. An increase in the vehicle's speed directly increases the thinking distance – the faster the vehicle, the further it travels before the driver reacts. Driver reaction time can be impaired by various factors including fatigue, distraction (e.g., mobile phone usage), consumption of alcohol, or drugs. Any impairment to reaction time will lead to a longer thinking distance, thereby increasing the overall stopping distance and reducing safety.

Factors Affecting Braking Distance

Braking distance is influenced by several factors: the vehicle's speed, the condition of the road surface, the condition of the vehicle's tires, and the effectiveness of the brakes. A higher speed significantly increases the braking distance, following a relationship where braking distance increases approximately with the square of the speed. Wet or icy roads reduce friction, extending braking distance. Worn tires or faulty brakes also decrease the available friction or braking force, leading to longer braking distances. All these factors contribute to the overall safety implications.

Implications for Road Safety

Understanding the factors that affect stopping distance is crucial for road safety. Longer stopping distances mean a driver has less time and space to react to sudden hazards, significantly increasing the likelihood of collisions. High speeds, impaired driving, poor vehicle maintenance, and adverse weather conditions all extend stopping distances, leading to a greater risk of accidents and more severe consequences if an accident does occur. Adhering to speed limits, maintaining vehicles, and avoiding distractions are essential practices to minimise stopping distances and enhance safety for all road users.

The Transformer Equation (Higher)

Transformers are devices that change the voltage of an alternating current. An ideal transformer obeys the relationship: Vp / Vs = Np / Ns. Here, Vp is the potential difference across the primary coil, Vs is the potential difference across the secondary coil, Np is the number of turns in the primary coil, and Ns is the number of turns in the secondary coil. A step-up transformer has Ns > Np, meaning it increases voltage (Vs > Vp). A step-down transformer has Ns < Np, meaning it decreases voltage (Vs < Vp). This equation is fundamental for calculating voltage and turns ratios in ideal transformers.

Power Transfer in Ideal Transformers (Higher)

For an ideal transformer, it is assumed that there are no energy losses. This means the power supplied to the primary coil is equal to the power transferred from the secondary coil. The power in an electrical circuit is given by P = VI (Power = Voltage × Current). Therefore, for an ideal transformer, the power in the primary coil (Pp) equals the power in the secondary coil (Ps): VpIp = VsIs. This implies that if the voltage is stepped up, the current must be stepped down proportionally to conserve power, and vice versa. Real transformers have some energy loss, mainly due to heating in the coils and core, but this ideal model is a good approximation for most calculations.

Advantages of High Voltage Power Transmission (Higher)

Transmitting electrical power at high voltages significantly reduces energy loss over long distances. The power lost in transmission cables is primarily due to resistance heating, calculated by the formula P_loss = I^2R, where I is the current flowing through the cables and R is the resistance of the cables. By using a step-up transformer to increase the voltage, the current (I) in the transmission lines is drastically reduced for a given amount of power being transmitted (since P = VI, so I = P/V). Because the power loss is proportional to the square of the current (I^2), even a small reduction in current leads to a much larger reduction in energy loss. This makes the National Grid's high-voltage transmission system very efficient.

Applying the Principles (Higher)

When solving problems involving transformers and power transmission, it's crucial to identify whether a transformer is step-up or step-down. Remember that for a step-up transformer, Vs > Vp and Is < Ip, while for a step-down transformer, Vs < Vp and Is > Ip. The two key equations, Vp / Vs = Np / Ns and VpIp = VsIs, allow you to calculate unknown voltages, currents, or turns given sufficient information. Always consider the practical implications of high voltage transmission, particularly the safety aspects and the need for step-down transformers near consumers.

Speed Estimation for Road Vehicles

Estimating the speed of road vehicles involves knowing typical speeds in various scenarios. A car in a residential area might travel at 5-10 m/s (around 10-20 mph). On main roads, speeds often range from 15-20 m/s (around 30-45 mph). Motorway speeds can be around 25-30 m/s (approximately 55-70 mph). It's important to be able to convert between m/s and mph for better contextual understanding, even though exact conversions aren't always required for estimation. Remember that 1 m/s is approximately 2.2 mph.

Estimating Acceleration in Road Transport

Acceleration is the rate at which velocity changes. A 'large acceleration' for a car means it is rapidly increasing its speed. For a typical family car, hard acceleration from a standstill might be estimated around 3-5 m/s². High-performance sports cars can achieve much higher accelerations, possibly in the range of 6-10 m/s² or more. It's rare for everyday vehicles to sustain very high accelerations for long periods. When a driver 'puts their foot down' for rapid overtaking, they are seeking a large acceleration.

Forces Involved in Large Accelerations

The forces involved in large accelerations are directly linked to Newton's Second Law: Force (F) = mass (m) × acceleration (a). To estimate the force, you need an approximate mass of the vehicle and an estimated acceleration. A typical car has a mass between 1000 kg and 1500 kg. A large acceleration (e.g., 4 m/s²) multiplied by a typical car mass (e.g., 1200 kg) yields a large force (4800 N). These engine forces must overcome air resistance, friction, and the vehicle's own inertia to produce acceleration. Braking forces can also be very large when a vehicle decelerates quickly.