Energy can never be created or destroyed, it is only ever converted from one store to another usefully or dissipated into the surroundings.
It is important that you can identify key energy transfers in common electrical appliances including both useful and wasted energy. For example, in a kettle, food processor or lamp.
Energy transfers as useful energy, or it is stored, or it is dissipated into the surroundings. Questions can include common transfers you are familiar with, or new machinery that you will have to read the information given carefully to write your answers.
Sankey diagrams are used to visually represent the efficiency of an energy transfer, for example the efficiency of an electronic device.
In a closed system energy and matter cannot leave the system, therefore the energy input will equal the energy output.
Efficiency is the ratio of useful work done by a machine compared to the total energy supplied. It is calculated using the equation in the shown image.
A battery powered electric motor is used to lift a load. Fully describe the energy transfer that occurs from the battery to the load lifted by the electrical motor.
As ball is thrown into the air kinetic energy is transferred into gravitational potential energy as it rises. Suggest a reason why the maximum amount of kinetic energy is greater than the maximum gravitational potential energy when the ball gets to its peak.
An electric fan has the power of 3 W and is running for 20 minutes. In the time it is on 2400 J of energy is transferred usefully. Draw a Sankey diagram to illustrate the energy transfer of the fan. You are not required to find the wasted energy in this case.
What kind of change in energy can occur in a closed system? A) energy can be dissipated to the surroundings, B) energy can be transferred from one form to another, C) energy can be gained from the surroundings.
A girl sits on top of a 1.5 m high slide and weighs 40 kg as shown in the diagram. Assuming that it is a closed energy system, how much kinetic energy does she have when she reaches the bottom of the slide?
A washing machine converts electrical energy into useful kinetic and heat energy, but energy is also dissipated to the surroundings in the form of heat and sound. The washing machine is 65% efficient, if 500 J are converted into useful energy, how much energy is wasted?
A hairdryer is on for 600 seconds and has a power rating of 8 W. The hairdryer transfers 300 J of useful energy over the time it is running, by using the equations shown, what is the efficiency of the hairdryer?
A phone charger converts electrical energy into chemical energy stored in the phone’s battery. 270 J is transferred to the phone’s battery every minute and the charger is 90% efficient. By working out the efficiency of the phone charger, calculate the power rating of the charger.
Two televisions are both supplied with the same amount of energy and they transfer energy at the same rate, but television A wastes more energy than television B. Which one of the two televisions (A or B) is the most efficient? Explain your answer.
When a ball is thrown in the air, as shown in the diagram, it is given 30 J of energy. Using the conservation of energy, what type of energy and how much energy does the ball have of different energy stores at points A, B and C shown in the diagram? Assume that the ball stops at the point C and B is exactly in the middle of A and C.
A simple pendulum swings and small amounts energy is lost to the surroundings as it continues to swing. When the pendulum reaches the top of its swing, point x shown in the diagram, all its energy is stored as gravitational potential energy. How is the energy in the pendulum transferred as the pendulum swings, and how does this effect the speed it is travelling? Use points y and z in the diagram as reference points in your answer.