1a. Energy Transfers Flashcards
State the 8 different forms of energy store.
Thermal (or internal) energy store
Kinetic energy store
Gravitational potential energy store
Elastic potential energy store
Chemical energy store
Magnetic energy store
Electrostatic energy store
Nuclear energy store
What is meant by a closed system?
A closed system is a system where neither matter nor energy can enter or leave.
State the conservation of energy principle.
Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed.
Which of these has the most energy in its kinetic energy store: a small dog walking slowly or a large dog running fast? Why?
The large dog has more energy in its kinetic energy store, because the energy in this store is related to mass and speed by Ek = 0.5mc2
What is the formula for calculating the energy in an object’s kinetic energy store? What does each term represent and what units should they be in?
Ek = 0.5mc2. Ek is the energy in the kinetic energy store in J, m is mass in kg and v is speed in m/s.
What is the formula for working out the energy transferred to an object’s gravitational potential energy store? What does each term represent and what units should they be in?
Ep = mgh. Ep is the energy transferred to the gravitational potential energy store in J, m is mass in kg, g is gravitational field strength in N/kg and h is height in m.
What is the formula for working out the energy transferred to an object’s elastic potential energy store? What does each term represent and what units should they be in?
Ee = 0.5ke2. Ee is the energy in the elastic potential energy store in J, k is the spring constant in N/m and e is extention (or compression) in m.
What is the specific heat capacity of a substance?
The amount of energy needed to change the temperature of 1kg of a substance by 1 UNIT
What is meant by the term ‘power’?
Power is the rate of doing work, i.e. how much work is done (or energy is transferred) per second.
State the equations for power. What does each term represent and what units are they measured in?
P = E/t and P = W/t. P is power in watts, E is energy transferred in joules, W is work done in joules and t is time in seconds.
What is conduction? Describe how energy is transferred by conduction.
The transfer of energy by heating through a substance by vibrating particles colliding. The particles of the part of the substance that is heated have more energy in their kinetic energy stores and vibrate more. The particles collide with thir neighbouring particles and pass on some of this energy, causing energy eventually to be spread out through the substance.
What is convection?
Convection is the transfer of energy by the movement of more energetic particles in a gas or liquid from a hotter to a cooler region.
In which state of matter does convection not happen?
Solids (Particles in a solid can only vibrate about their fixed positions, they can’t move from one place to another and take their energy with them)
Explain how installing each of the following types of insulation helps reduce unwanted energy transfers from a home. a) Cavity wall insulation b) Loft insulation c) Double glazing
a) Foam installed in the gap between the bricks of a cavity wall stops convection currents being set up in the gap. b) An insulating material laid on a loft floor reduces conduction through the loft floor and prevents convection currents forming in the loft space, which helps reduce energy transferred out of thermal energy stores in the house. c) Double-glazed windows have a double layer of glass separated by an air gap. Because air conducts poorly it will reduce energy loss by conduction through the window.
Give one example of when lubrication is used to decrease unwanted energy transfers.
E.g. A lubricant (e.g. oil) can be used on an axle in a fan to decrease the friction between the axle and its support and so decreases the unwanted energy transfers to thermal energy stores due to friction.
