Energy Systems and Resources

A system is simply an object or group of objects that can store energy in different ways. When energy transfers occur within a system, energy can be stored, transferred usefully, or dissipated – but it can never be created or destroyed. This is one of the fundamental laws of physics!

Energy is often "wasted" during transfers, meaning it's stored in less useful forms (usually as heat). Materials with high thermal conductivity transfer energy more quickly through conduction. This explains why metal feels cold to touch – it's rapidly conducting heat away from your hand!

The main energy resources available include fossil fuels (coal, oil, gas), nuclear fuel, bio-fuel, wind, hydro-electricity, geothermal, tides, solar and water waves. A renewable energy resource can be replenished as it's used, unlike finite resources like coal or oil.

Did you know? All the energy we use for electricity, transport and heating originally comes from the Sun, nuclear reactions, or the Earth's internal heat!

Standard circuit diagrams use specific symbols to represent different components, including switches, cells, batteries, diodes, resistors, LEDs, lamps, and measuring instruments like voltmeters and ammeters.

Electric Circuits and Components

Electrical charge flows through a closed circuit only when there's a source of potential difference (voltage). Electric current is the flow of this charge, and its size represents how quickly charge is flowing. The clever bit is that current has exactly the same value at any point in a single closed loop!

The relationship between current (I), resistance (R), and potential difference (V) is crucial. The current through a component depends on both the resistance of the component and the potential difference across it. When resistance increases, the current decreases for the same potential difference.

Some components have constant resistance while others don't. In an ohmic conductor (like a metal wire at constant temperature), the current is directly proportional to the potential difference – this means the resistance stays constant. This is what we call Ohm's Law.

However, components like lamps, diodes, thermistors, and LDRs have resistance that changes:

• Filament lamp resistance increases as temperature rises
• Diodes allow current to flow in one direction only (they have extremely high resistance in reverse)
• Thermistor resistance decreases as temperature increases
• LDR (Light Dependent Resistor) resistance decreases as light intensity increases

Exam tip: Remember that graphs showing current against potential difference can tell you whether a component follows Ohm's Law (straight line) or not (curved line).

Circuit Arrangements and Mains Electricity

There are two ways to connect components in circuits: series and parallel. Many real circuits contain both arrangements. The behavior of these circuits follows specific rules that you need to know for your exams.

In series circuits:

• The same current flows through each component
• The total potential difference is shared between components
• The total resistance equals the sum of individual resistances

In parallel circuits:

• Each component has the same potential difference across it
• The total current equals the sum of currents through each branch
• The total resistance is less than the smallest individual resistor

Mains electricity in the UK is an alternating current (AC) supply with a frequency of 50 Hz and approximately 230 volts. Most appliances connect to the mains using a three-core cable with color-coded insulation for safety:

• Live wire (brown) – carries the alternating potential difference
• Neutral wire (blue) – completes the circuit
• Earth wire (green and yellow) – safety wire to prevent appliances becoming live

The potential difference between live and earth is about 230V, while the neutral wire stays close to 0V. The earth wire normally carries no current unless there's a fault. Remember that a live wire can be dangerous even when a switch is open!

Safety note: Never mess around with mains electricity – the voltages involved can be lethal.

Electrical Power and Energy Changes

Everyday electrical appliances convert energy from one form to another. The amount of energy transferred depends on how long the appliance runs and its power rating. Work is done whenever electric charge flows in a circuit – this is the principle behind all electrical devices.

The National Grid is the system that distributes electricity from power stations to consumers across the country. It uses transformers to manage voltage efficiently:

• Step-up transformers increase voltage for transmission through power lines (reducing energy losses)
• Step-down transformers decrease voltage to safer levels for domestic use

Changes of state (solid to liquid to gas) are physical changes, not chemical ones. If you reverse a physical change, the material returns to its original properties. When substances change state, the particles themselves don't change – only their arrangement and energy.

Internal energy refers to the total energy stored inside a system by its particles. It combines both the kinetic energy (movement) and potential energy (position) of all atoms and molecules that make up the system. When you heat something, you're changing the energy stored within the system.

Think about it: When you boil water, you're adding energy that increases the internal energy of the water molecules until they have enough energy to escape as steam!

Changes of State and Internal Energy

Heating changes the internal energy of a system, which can either raise its temperature or cause a change of state. The temperature increase depends on three factors: the mass being heated, the type of material, and the energy input.

Every substance has a specific heat capacity – the amount of energy needed to raise the temperature of one kilogram of the substance by one degree Celsius. Materials with high specific heat capacities (like water) take more energy to heat up than those with low values.

When a substance changes state (like ice melting to water), the energy supplied changes the internal energy but not the temperature. This energy is called latent heat. The specific latent heat of a substance tells us how much energy is required to change the state of one kilogram without changing its temperature.

There are two important types of latent heat:

• Specific latent heat of fusion – energy for changing from solid to liquid
• Specific latent heat of vaporisation – energy for changing from liquid to gas

In gases, molecules move in constant random motion. The temperature of a gas is directly related to the average kinetic energy of its molecules. If you change the temperature of a gas in a sealed container, the pressure will change as the molecules hit the container walls with different forces.

Practical application: Understanding specific heat capacity helps engineers design efficient heating systems, while knowledge of latent heat is crucial for refrigeration and air conditioning!

Atomic Structure

Atoms are incredibly tiny, with a radius of about 0.0000000001 meters $10^-10 m$. The basic structure of an atom includes a positively charged nucleus (containing protons and neutrons) surrounded by negatively charged electrons.

Most of an atom's mass is concentrated in the nucleus, but the nucleus is less than 1/10,000 of the atom's radius! Electrons are arranged at different distances from the nucleus in what we call energy levels. These arrangements can change when atoms absorb or emit electromagnetic radiation.

When an atom absorbs electromagnetic radiation, electrons can move to higher energy levels (further from the nucleus). When electrons fall to lower energy levels (closer to the nucleus), they emit electromagnetic radiation. This principle explains how stars shine and how fluorescent lights work!

In atoms, the number of electrons equals the number of protons, giving atoms no overall electrical charge. All atoms of a particular element have the same number of protons – this is called the atomic number. The mass number is the total number of protons and neutrons.

Isotopes are atoms of the same element with different numbers of neutrons. This means they have the same atomic number but different mass numbers. When atoms lose one or more outer electrons, they become positive ions.

Fun fact: Carbon has several isotopes including carbon-12 and carbon-14. The latter is radioactive and is used to date ancient organic materials in archaeology!

The Development of Atomic Models and Radioactivity

The model of the atom has evolved dramatically with new evidence. Before the electron's discovery, atoms were thought to be indivisible spheres. When the electron was discovered, the plum pudding model suggested atoms were positive spheres with embedded negative electrons.

The famous alpha particle scattering experiment led to the nuclear model, showing that an atom's mass was concentrated in a small, charged nucleus. Niels Bohr later improved this by proposing that electrons orbit the nucleus at specific distances – his calculations matched observations!

Later discoveries revealed that the nucleus contained positively charged protons. About 20 years after the nucleus became accepted, James Chadwick provided evidence for neutrons within the nucleus, completing our basic understanding of atomic structure.

Some atomic nuclei are unstable and undergo radioactive decay to become more stable, emitting radiation in a random process. The activity of a radioactive source is the rate at which nuclei decay, measured in becquerel (Bq). A detector like a Geiger-Muller tube measures the count-rate (decays per second).

Nuclear radiation can take several forms:

• Alpha particles (α) – two neutrons and two protons (identical to a helium nucleus)
• Beta particles (β) – high-speed electrons ejected as neutrons turn into protons
• Gamma rays (γ) – electromagnetic radiation from the nucleus
• Neutrons (n) – neutral particles from the nucleus

Exam tip: Remember that radioactive decay is a random process – you can't predict exactly when a particular nucleus will decay, but you can predict the behaviour of a large sample statistically.

Radioactivity and Half-Life

The half-life of a radioactive isotope is the time taken for the number of unstable nuclei in a sample to halve, or for the count rate (activity) to fall to half its initial level. This concept is crucial for understanding radioactive decay and dating techniques.

Radioactive decay is completely random - we can't predict when an individual nucleus will decay. However, with large numbers of atoms, the decay follows a predictable pattern. This is why half-life is such a useful measurement - it gives us a way to predict how much of a radioactive sample will remain after a certain time.

Radioactive materials can be dangerous because the radiation they emit can damage living cells. The effects depend on the type and amount of radiation, and the part of the body exposed. Different types of radiation have different penetrating powers, which affects how they're handled safely.

Understanding the properties of different radiations is essential for their practical applications. For example, alpha radiation might be used in smoke detectors, while gamma radiation can be used to sterilize medical equipment or treat cancer.

Real-world application: Medical professionals use radioactive tracers with short half-lives for diagnostic procedures, ensuring the radioactive material decays quickly after serving its purpose!