P1: Flashcards
What are the energy stores?
Thermal energy stores
Kinetic energy stores
Gravitational Potential energy stores
Elastic potential energy stores
Chemical energy stores
Magnetic energy stores
Electrostatic energy stores
Nuclear energy stores
What are the energy transfers?
Mechanically (by a force doing work)
Electrically (work done by moving charges)
Heating
Radiation (e.g. light or sound)
What is a closed system?
Neither matter nor energy can enter or leave.
What is work done?
Moving an object with an applied force.
Describe the energy transfers that occur when the wind causes a windmill to spin.
Energy is transferred mechanically [1 mark] from the kinetic energy store of the wind [1 mark] to the kinetic energy store of the windmill [1 mark].
What is the calculation for kinetic energy?
Ek (J) = 1/2 x m x v^2
What is the equation for gravitational potential energy?
Ep (J) = mgh
What is the word equation for a falling object when there’s no air resistance?
Energy lost from the g.p.e store = energy gained in the kinetic energy store
What is the equation for elastic potential energy?
Ee (J) = 1/2 x k (spring constant N/m) x e^2 (extension)
What is the conservation of energy principle?
Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed.
What are the equations for power?
P = E (energy transferred)/t. P = W (work done)/t
What is power?
The rate of energy transfer, or the rate of doing work.
How can wasted energy be reduced?
- Lubrication
• Oil in a motor
• Reduces friction
• So less energy is lost (as heat) through friction - Thermal Insulation
• Double Glazing
• Less useful thermal energy lost
What is the equation for the efficiency for any energy transfer?
Efficiency = useful output energy transfer / total input energy transfer
Efficiency = useful power output / total power input
What device is usually 100% efficient?
Electric heaters because all the energy in the electrostatic energy store is transferred to useful thermal energy stores.
