energy - physics

• energy stores is a system (an object or group of object) and when a system changes the way energy is stored also changes
• examples of energy transfer is a ball rolling and hitting a wall , the system is the moving ball and the when it hits the wall some of the kinetic energy transferred as sound
• kinetic energy is Ek (kinetic energy)= 1/2 x m (mass-kg) x v2 (speed squared- metres per second)
• elastic potential is Ee (elastic potential)= 1/2 x k (spring constant-N/m) x e (extension-metres)
• gravitational potential energy is Ep (gravitational energy) = m (mass) x g (gravitational field strength-N/kg) x h (height in metres)
• specific heat capacity is energy = mass x specific heat capacity x temperature change
• energy can be transferred usefully and stored or dissipated but cannot be created or destroyed , but a store used in less useful ways this energy is often described as being 'wasted'
• you can reduce energy waste by using lubrication or thermal insulation to reduce friction
• thermal conductivity is when heat is allowed to travel through the material more easily and if it has a higher thermal conductivity is will pass through quicker
• efficiency is the ratio of the useful work done by machine, energy, device, etc, to the energy supplied to it, often expressed as a percentage
• the equation for efficiency is efficiency = useful energy output/total energy input or useful power output/total power input
• the efficiency of a system can be increase by: reducing waste output (lubrication, thermal insulation), recycling waste output (absorbing thermal waste and recycling as input energy)
• main energy sources are known as non-renewable and renewable , some examples of non-renewable are fossil fuels and nuclear fuel and renewable is biofuel, wind, hydroelectricity, geothermal, tidal, solar and water waves
• renewable energy is energy which can be replenished as it is used (e.g. wind will never stop)
• non-renewable energy is used more for large-scale energy supplies due to the large energy output per kilogram of fuel - renewable resources cannot provide such a large amount of energy as easily
• renewable energy has become more important due to the finite lifetime of fossil fuels, and so their development has become more important
• renewable energy is not always the most reliable as: solar doesn't work in bad weather or night, wind is only intermittent.
• some main energy uses are: transport, electricity generation and heating
• environmental impact includes extraction of energy for example fossil fuels destroying landscapes and wind turbines can be considered an eyesore
• environmental impact as a use of energy source is fossil fuels release harmful emissions and solar, wind directly create electricity with no emissions
• revision .

  
• current is the flow of electrical charge and the greater the rate of flow of charge , greater current ( Q= I X t )
• Q is the charge flow, in coulombs ( C ) and I is the current in amperes ( A ) and t is the time in seconds
• the greater the resistance of the component the smaller the current for a given potential difference ( pd ) across the component
• current, potential difference or resistance can be calculated using the equation: V = I x R
• resistors is constant , an ohmic conductor , current is directly proportional to the potential difference , in case the graph is linear
• is the resistance of components through the component , so the graph is nonlinear , for example the resistance of a filament lamp increases as the temperature of the filament increases and the current through a diode flows in one direction only , so it has a higher resistance in the reverse direction
• resistance can change as current increases as electrons (charge) has more energy , when electrons flow through a resistor they collide with the atoms in the resistor and this transfers energy to the atoms causing them to vibrate more
• resistance can change with temperature when atoms hot they vibrate more, thermistor in hotter temperature the resistance is lower
• resistance can change with length if its greater the more resistance and the lower the current , electrons have to make their way through more resistor atoms so it is harder than using a shorter wire
• resistance change with voltage as diodes allows current to flow freely in one direction and in the opposite direction it has a very high resistance so no current can flow
• series circuits are closed circuit which the current only follows a single path and the current is the same everywhere
• parallel circuits is a branched circuit when the current splits into multiple paths and the total current into a junction = total current in each of the branches and the potential difference is the same across each branch
• power is energy transferred per second and is directly proportional to current and voltage