Energy Energy can neither be created or destroyed, only changed into different forms. Energy is only useful when it can be converted into different forms. Energy is often dissipated – spread out and lost. 9 types of energy: Thermal (heat) – flows from hot to cold objects Kinetic (movement) – anything that is moving has this Light – from the sun, light bulbs et cetera Elastically potential – when things are stretched Gravitational potential – anything that can fall Electrical – whenever a current flows Sound – vibrations in the air Chemical -a store of energy e. G. Batteries, food et cetera
Nuclear – released in nuclear reactions E. G. A television gives out light, sound and heat. Potential and chemical energy are all stores of energy because they are not actively doing anything but waiting to be changed into another type of energy. To understand energy transfer, we must understand particles, States of Matter Substances can have different states of matter: The state of matter that a substance is depends on the amount of energy that each of the particles has. Substances can change between states of matter: As particles gain kinetic energy, they spread out more, therefore becoming liquid and then gas.
When particles lose energy, they spread out less and therefore become liquid and then solid. Heat energy is energy on the move. Moving from places of high temperature to areas of low temperature. The bigger the temperature difference, the faster the heat transfer. Heat moves by three different processes: Conduction – mainly in solids Convection – mainly in liquids and gases Radiation – any state of matter can absorb/emit infrared radiation. Vibrations in matter are passed on to transfer heat energy. This is called conduction. Insulator – a material that stops energy being transferred.
Solids are good conductors because the particles are closer together and so the particles collide more frequently. Good conductors have free electrons. Metals contain free electrons and so they are good conductors. Free electrons increase conductivity because they move faster and so collide with other particles more. Note: Good conductors often feel hotter/colder than the surroundings however this is not the case. Actually, the material is Just conducting the heat into/away from your hand faster. Infrared Radiation All objects continually emit and absorb infrared radiation.
It is emitted from the reface of an object. An object that is hotter than its surroundings will emit more radiation than it absorbs as it cools down and vice versa when an object is cooler than its surroundings. The hotter an object is, the more radiation it gives out in a given time. Radiation and Surfaces Good emitters and absorbers: Dark, Matt surfaces Bad emitters and absorbers: light, shiny surfaces. These reflect infrared radiation. Convection Convection occurs mostly in liquids and gases when more energetic particles move from hotter regions to cooler regions and take their heat energy with them.
Particles main kinetic energy when they are heated, making the substance less dense. This makes the particles rise. Particles then lose energy in colder areas, causing the particles to become more dense and so sink. A steady flow of particles between warm and cold is called a convection current. Convection currents cause sea breezes in which air warmed by the land rises and is replaced by colder air from above the sea. Tip: always state the type of heat transfer involved. Rate of Heat Transfer Factors that affect heat transfer: Surface area – the larger the surface area, the more IR radiation can be emitted or absorbed e. . Radiators have a high surface area. Proportion of surface area to volume Type of material – Good conductors will increase the rate of heat transfer. Temperature difference Some products are designed to decrease the rate of heat transfer e. G. Flasks: Have double walls with a vacuum in the middle, stopping all conduction and convection. The walls are silver to reduce radiation. Humans and Animals also Control Heat Transfer In cold, hair or fur ‘stand up’ to trap a thick layer of insulating air, keeping the body be lost through radiation. Animals in hot climates have large surface areas e. G.
Desert foxes and elephants have huge ears. Evaporation and Condensation Condensation – when gas turns to liquid because the particles do not have enough energy to resist the attractive forces that pull them together. This happens when a gas cools down. Evaporation – when liquid turns to gas because the particles gain enough energy to resist the attractive forces and so become less dense – a gas. The fastest particles (with the most energy) escape first, leaving the particles with less energy. This causes a decrease in average particle energy meaning that the temperature of the remaining liquid falls. E. G.
Sweating cools us down because liquid evaporates from our skin. Rates of Evaporation and Condensation Efficiency Devices are useful because they convert energy from one form into another. Some of the input energy is always wasted, usually as heat, whilst the rest is useful. A device is more Useful Energy out efficient the less energy that is wasted. Total Energy in Efficiency = The formula can be re-arranged and also used to calculate power efficiency. No device is 100% efficient as wasted energy is usually spread out as heat and dissipated. An exception to this is electric heaters in which all of the energy is inverted to heat.
Other factors have to be considered when buying an appliance e. G. A lightly Low energy light bulb is 4 times more efficient than an ordinary bulb. Energy efficient light bulbs are more expensive but last longer. LED bulbs are even more energy efficient but are more expensive and do not give as much light. When appliances are chosen, cost effectiveness, price and efficiency all are factors of the decision. Useful Waste Energy Sometimes, wasted heat energy can be used. Heat exchangers reduce the amount of heat that is lost and use the ‘wasted’ energy for other purposes.
They do this by pumping cold water around the appliance, causing the liquid to increase temperature. This energy can be used for many purposes. E. G. Heat from car engines can be transferred to warm the passenger compartment. Energy efficiency in the home conduction from the house into the environment. Loft insulation – a thick layer of fiberglass wool reduces energy transfer from the house to the environment (conduction and radiation). Draught proofing – stops draughts of cold air so reduces convection. Et cetera Heat transfers faster through materials with higher I-I-values Specific Heat Capacity
It takes more energy to heat some materials than others. Materials that take a lot of energy to heat up also release a lot of energy when they cool down. This means that they can store a lot of energy. Specific heat capacity is a measure of how much energy a substance can store. E = B E- energy 0) m- mass (keg) c- specific heat capacity 0/keg) e- temperature change (co) Energy Transformation Diagrams Snakes diagrams can be used to show the total energy in compared to the useful and wasted energy out. The thicker the arrow, the more energy it represents. These diagrams can be sketched or detailed.