Summary
Highlights
In series circuits, total PD is shared, current is constant, and total resistance sums up. In parallel circuits, PD is the same across branches, current is shared, and adding more resistors decreases total resistance. Thermistors (resistance decreases with increased temperature) and LDRs (resistance decreases with increased light intensity) are discussed as variable resistors used in sensor circuits.
Energy is a conserved concept, not created or destroyed. Key energy 'stores' include kinetic energy (1/2 mv^2), gravitational potential energy (mgh), elastic potential energy (1/2 kx^2), and thermal energy (E=mcΔT). Energy is transferred between these stores within a system. Real-world examples like a roller coaster convert GPE to kinetic energy. Efficiency measures the useful energy transferred versus total energy input. Non-renewable (fossil fuels, nuclear) and renewable (wind, solar, geothermal, biofuel) energy sources are also covered.
Electrical power is the rate of energy transfer, calculated as P=VI or P=I^2R. Mains electricity uses AC (alternating current) and alternating PD, typically at 230V and 50Hz, compared to DC (direct current) from batteries. Safety features in plugs, such as live, neutral, and earth wires, and fuses (selected based on appliance current), are explained. The National Grid uses transformers to step up voltage for efficient transmission and then step down for safe domestic use.
Static electricity is created by friction-induced electron transfer, leaving objects with opposite charges that attract, or like charges that repel. The concept of electric fields, represented by field lines, is introduced, showing the direction of force on a positive charge. Uniform fields exist between parallel plates, while radial fields surround single charged objects (e.g., a Van de Graaff generator).
Density (ρ = m/V) is a measure of how compact mass is. Methods for finding the volume of regular (using dimensions and tools like vernier calipers or micrometers) and irregular (using displacement cans) objects are detailed. The three states of matter (solid, liquid, gas) are described based on particle arrangement and movement. Energy changes during phase transitions (melting, evaporation) are explained, highlighting that temperature remains constant during these changes as energy goes into increasing internal potential energy rather than kinetic energy. The total internal energy is the sum of kinetic and potential energies of particles.
Heating a gas increases particle kinetic energy, leading to more forceful and frequent collisions with container walls, thus increasing pressure. Compressing a gas also increases pressure by doing work on it. For a gas at constant temperature, pressure and volume are inversely proportional (P1V1 = P2V2).
The historical development of atomic models (Thomson's plum pudding, Rutherford's nuclear model, Bohr's electron shells, Chadwick's neutron discovery) is briefly outlined. Atoms consist of a nucleus (protons and neutrons) and orbiting electrons. Atomic number (protons) defines the element, while mass number (protons + neutrons) indicates its mass. Isotopes are atoms of the same element with different numbers of neutrons.
Radiation refers to emitted particles or waves. Gamma radiation (high-energy EM waves) is emitted by the nucleus. Alpha and Beta radiation are particles emitted during nuclear decay. Nuclear decay equations are demonstrated for alpha (emission of helium nucleus) and beta (neutron decays into a proton and electron) decay. Ionizing ability and penetration power differ significantly for alpha (high ionizing, low penetration), beta (moderate), and gamma (low ionizing, high penetration) radiation.
A GM tube detects radiation. Background radiation (from radon gas, cosmic rays, man-made sources) must be accounted for by taking a corrected count. Radioactivity (activity) is the rate of decay, measured in becquerels (Bq). Half-life is the time it takes for the number of unstable nuclei, and thus activity, to halve. How to determine half-life from a graph and through calculation is explained.
Nuclear fission is the splitting of a heavy nucleus (e.g., uranium) after absorbing a neutron, releasing energy, daughter nuclei, and more neutrons, leading to a chain reaction. This process is used in nuclear reactors for controlled energy generation. Nuclear fusion is the joining of two light nuclei (e.g., hydrogen) to form a heavier one, releasing immense energy (as seen in the sun). Scientists are working on harnessing fusion energy.
Every measurement has a unit, and prefixes (like kilo-, micro-) are used for very large or small numbers. Conversion between units often involves multiplying or dividing by factors of a thousand, except for centimeter and decimeter. Standard form (e.g., 5 x 10^-6 for 5 micrometers) is also discussed for expressing these numbers.
Electricity is the flow of charge (electrons). Current is the rate of flow of charge (I = Q/t). Potential difference (voltage) is the energy transferred per unit charge (V = E/Q). Resistance is a component's opposition to current flow (Ohm's Law: V = IR). Voltmeters are connected in parallel, ammeters in series. The IV characteristics for resistors (ohmic), filament lamps (non-ohmic due to temperature increase), and diodes are explained.