Radioactive decay - waves and particles Revision Notes

Non-Renewable Energy Sources

Non-renewable energy sources are natural resources that cannot be restored to their original state quickly enough to keep pace with consumption. They have a finite supply. The main types are fossil fuels (coal, oil, natural gas) and nuclear fuels (uranium). Fossil fuels are formed from ancient organic matter over millions of years and release carbon dioxide when burned, contributing to global warming. Nuclear fuels provide energy through nuclear fission, producing no greenhouse gases during operation but generating radioactive waste that needs secure long-term storage. These sources are currently widely used but will eventually run out.

Renewable Energy Sources

Renewable energy sources are those that are naturally replenished on a human timescale. They are considered sustainable and generally have a lower environmental impact during operation compared to non-renewable sources. Examples include solar (from sunlight), wind (from wind turbines), hydroelectric (from flowing water), geothermal (from Earth's internal heat), and biomass (from organic materials). While they significantly reduce carbon emissions, some renewable sources can be intermittent (e.g., solar and wind depend on weather) and may have high initial installation costs or local environmental impacts, such as visual intrusion from wind farms.

Uses of Energy Sources

Energy sources are used for various purposes. Electricity generation is a primary use, with both fossil fuels and nuclear power providing a consistent base load. Renewable sources are increasingly integrated into electricity grids. Fossil fuels are also critical for transportation (petrol, diesel) and industrial processes. Natural gas is widely used for domestic heating. Renewable sources like solar panels on roofs provide heating and electricity for individual homes, while biomass can be burned for heat or converted into biofuels for transport. Hydroelectric power is a major source of electricity in some regions.

Comparing Energy Source Characteristics

When comparing energy sources, key characteristics include renewability, environmental impact (especially greenhouse gas emissions), reliability of supply, and cost. Non-renewables (fossil fuels, nuclear) offer high energy density and reliability but contribute to climate change (fossil fuels) or radioactive waste (nuclear). Renewables (solar, wind, hydro) are sustainable and generally cleaner, but can be intermittent, require large land areas, and may have higher upfront costs. Energy policies often aim to balance these different characteristics to ensure a secure, affordable, and sustainable energy supply.

Functions of Mains Wires

Mains electricity in the UK generally uses three wires: live, neutral, and earth. The live wire (brown) carries the alternating potential from the power supply, which is approximately 230 V relative to the ground. It is the most hazardous wire. The neutral wire (blue) completes the circuit and carries current away from the appliance, typically maintaining a potential close to 0 V (earth potential). The earth wire (green and yellow stripes) is a safety feature, providing a low-resistance path to the ground for fault currents, preventing the appliance casing from becoming live.

Potential Differences Between Wires

Understanding potential differences is key to electrical safety. The potential difference between the live wire and the neutral wire is approximately 230 V. Similarly, the potential difference between the live wire and the earth wire is also approximately 230 V. In contrast, the potential difference between the neutral wire and the earth wire is approximately 0 V under normal operating conditions, as both are effectively at ground potential.

Safety Implications

Touching the live wire is extremely dangerous due to the high potential difference (230 V) between it and the ground. The earth wire is critical for safety in appliances with metal casings. If a fault causes the live wire to touch the metal casing, a large current flows through the earth wire to the ground. This surge triggers a fuse or circuit breaker, disconnecting the power and preventing electric shock. Appliances protected by double insulation do not require an earth wire because their non-conductive casing prevents contact with live parts.

Wire Colour Codes (UK)

Standard colour codes for mains wiring are essential for identification and safety. In the UK, the live wire is identified by brown insulation. The neutral wire is identified by blue insulation. The earth wire is identified by green and yellow stripes. Correctly identifying these wires is fundamental for safe electrical installations and repairs.

Understanding Acceleration

Acceleration is defined as the rate of change of velocity. Since velocity includes both speed and direction, an object accelerates if its speed changes, its direction changes, or both. The formula for average acceleration is \( a = \frac{\Delta v}{t} \), where \( a \) is acceleration, \( \Delta v \) is the change in velocity (final velocity - initial velocity), and \( t \) is the time taken. The unit for acceleration is metres per second squared (m/s²). A positive acceleration indicates speeding up in the direction of motion, while a negative acceleration (deceleration) indicates slowing down.

Common Accelerations in Everyday Life

It's important to be able to estimate the magnitude of accelerations for various common scenarios. These estimates are not precise values but rather reasonable approximations. For example, the acceleration due to gravity near the Earth's surface is approximately 9.8 m/s², often rounded to 10 m/s² for simple calculations. This is a crucial reference point. Other examples include: a car accelerating from rest (~2-5 m/s²), a car braking sharply (~6-10 m/s²), a person walking or running (usually less than 2 m/s²), or a fast-moving train accelerating (~0.5-1 m/s²). These values help in making justified estimates.

Making Justified Estimates

To make a justified estimate of an acceleration's magnitude, you need to consider the initial speed, final speed, and the time taken for the change. If you can approximate these values, you can use the acceleration formula. For instance, if a bicycle goes from stationary (0 m/s) to 5 m/s in 2.5 seconds, its acceleration would be (5 - 0) / 2.5 = 2 m/s². If a car brakes from 20 m/s to 0 m/s in 4 seconds, its deceleration would be (0 - 20) / 4 = -5 m/s², so its magnitude of acceleration is 5 m/s². Always consider if your estimated value is reasonable compared to known everyday accelerations.

Alternating Current (a.c.)

The domestic electricity supply in the UK uses alternating current (a.c.). Unlike direct current (d.c.), which flows in one constant direction, a.c. periodically reverses its direction of flow. This type of current is generated efficiently at power stations and can be transmitted over long distances with minimal power loss, which is why it's chosen for the national grid. Most household appliances are designed to operate using a.c. electricity.

Frequency of UK Domestic Supply

The frequency of an alternating current refers to the number of complete cycles it performs per second. In the United Kingdom, the domestic electricity supply has a standard frequency of 50 Hertz (Hz). This means that the current reverses its direction and completes a full cycle of alternation 50 times every second. This consistent frequency is vital for the correct operation of many electrical devices, especially those that rely on timing, like electric clocks or motors.

Voltage of UK Domestic Supply

Voltage is a measure of the electrical potential difference between two points, providing the 'push' for electrons to move. The standard voltage for domestic electricity supply in the UK is approximately 230 volts (V). All household appliances sold in the UK are manufactured to safely and efficiently operate at this specific voltage. It's important to be aware of this voltage when considering electrical safety and when using appliances from other countries that may have different voltage standards.