4) Energy resources & transfers Flashcards
Units for mass, energy, velocity, acceleration, force, time, power
Mass = kilogram (kg)
energy = joule (J)
velocity = metre/second (m/s)
acelleration = metre/ second 2 (m/s2)
force = newton (N)
time = second (s)
power = watt (W)
Types of energy stores
-nuclear
-chemical - energy found in fuels, food, batteries. Transferred during chemical reactions
-magnetic - energy due to the force of attraction (or repulsion) between two magnets
-gravitational potential - energy an object has due to its position above the ground
-kinetic - energy an object has because its moving
-thermal - energy a substance has due to its temperature
-elastic potential - energy stored in a stretched spring/ elastic band
-electrostatic - energy due to the force of attraction (or repulsion) between
Different energy transfer mechanisms
-energy in stores aren’t fixed. Can be transferred from one to another
Mechanical - when a force acts on a body
Electrical - electricity can transfer energy from a power source
Heating - thermal energy can be transferred by conduction, convection or radiation
Radiation - light and sound carry energy and can transfer this between two points
Conservation of Energy
Energy cannot be created or destroyed, it can only be transferred from one store to another
-total amount of energy in a closed system remains constant
-no ‘lost’ but transferred into wasted energy
Efficiency
Efficiency = (useful energy output/ total energy input) x 100
-high efficiency: most of the energy transferred is useful
-low efficiency: most of the energy transferred is wasted
Sankey diagrams
-used to represent energy transfers
-end of the arrow pointing to the right - useful energy output
-end of the arrow pointing down - wasted energy
-width of arrow is proportional to the amount of energy going to each store
Conduction - materials
-metals are good at conducting heat
-non-metals, liquids and gases are poor - insulators
-materials containing small pockets of trapped air are good at insulating - air is a gas, poor conductor
Conduction
-When a substance is heated, the atoms start to move around (vibrate) more
-bump into each other, transferring energy from atom to atom
-Metals are especially good at conducting heat as the delocalised electrons can collide with the atoms, helping to transfer the vibrations through the material and hence transfer heat better
Convection - materials
-main way heat travels through liquids and gases
-cannot occur in solids
Convection
-The molecules push each other apart, making the fluid expand
-This makes the hot fluid less dense than the surroundings
-The hot fluid rises, and the cooler (surrounding) fluid moves in to take its place
-Eventually, the hot fluid cools, contracts and sinks back down again
-The resulting motion is called a convection current
Thermal radiation - materials
-Black objects: good emitters and absorbers of thermal radiation
-Shiny/ white objects: poor emitters and absorbers of thermal radiation
Thermal radiation
-all objects emit a spectrum of thermal radiation in the form of electromagnetic waves
-heat transfer by infrared
-hotter, more infrared radiation it radiates in a given time
Investigating conduction
- Attach ball bearings with wax to the ends of each metal strip at an equal distance from the centre
- The strips turned upside down and the centre heated gently using a bunsen burner so that each of the strips is heated at the central point where they meet
- When the heat is conducted along to the ball bearing, the wax will melt and the ball bearing will drop
- Time how long this takes for each of the strips and record in a table
- Repeat the experiment and calculate an average of each time
-first ball bearing to fall will be from the rod that is the best conductor
-should be: copper > aluminium > brass > iron
Investigating convection
- Fill the beaker with cold water and place it on top of a tripod and heatproof mat
- Pick up the potassium permanganate crystal using forceps and drop it into the centre of the beaker
- Heat the beaker using the Bunsen burner and record observations
- Repeat experiment with hot water and record observations
Investigating radiation
- Set up the four identical flasks painted black, grey, white and silver
- Fill the flasks with hot water, ensuring the measurements start from the same initial temperature
- Note the starting temperature, then measure the temperatures at regular intervals e.g. every 30 seconds for 10 minutes
