energy Flashcards
what are the two forms energy can take?
stored/potential energy and kinetic energy.
what is stored/potential energy?
energy stored in a substance with potential to be released.
examples of stored/potential energy?
chemical potential energy, gravitational potential energy, elastic potential energy, electrical potential energy.
what is kinetic energy?
energy in motion, actively using energy for move.
examples of kinetic energy?
heat energy, light energy, sound energy.
what kind of energy can travel through a vacuum?
electromagnetic energy, light energy, radiation.
contrast energy transfer and energy transformation.
energy transfer is when energy moves from one place to another while retaining its form, while energy transformation is when energy changes its form.
examples of energy transfer (transfers from what to what)?
- putting hot water in an aluminium cup- the heat energy transfers from the hot water to the aluminium cup.
- appliances- the electrical energy transfers from the power socket and through the wire/cord to the appliance (prior to its transformation into other types of energy).
- object vibrating- when an object vibrates, it produces sound waves that transfer through the air.
examples of energy transformation (transforms from what to what)?
- kettle- the electrical energy from the socket travels through the cord/wire to the kettle where it is - transformed into heat energy.
- windmill- the kinetic energy from the wind transfers to the turbines, causing them to move, transforming into electrical energy.
- solar panels- the heat energy from the sun is transformed into electrical energy.
what is the law of conservation of energy?
energy cannot be created or destroyed, only transferred or transformed from one form to another.
what are the three ways that heat can be transferred?
conduction, convection and radiation.
what is conduction?
- refers to the transfer of heat through direct contact between particles within a substance, without the actual movement of the substance as a whole.
- in conduction, heat energy is passed from one particle to the next within a material due to the collisions between them.
examples of conduction (transfers from what to what)?
- heating a pot on a stove- heat transfers from the stove to the pot.
- lizard warming its body on a rock- heat transfers from the rock to the lizard.
- toasting a marshmallow- heat transfers from the fire to the marshmallow.
what is convection?
- refers to the heat transfer that occurs through the movement of fluids (liquids or gases).
- the key principle behind convection is that as a fluid is heated, its particles gain kinetic energy and move more rapidly.
- this increased motion leads to a decrease in density.
- cooler, denser fluid then replaces the rising warm fluid, creating a continuous cycle of circulation.
examples of convection (transfers from what to what)?
- kettle- the water at the bottom gets heated first, which becomes less dense and rises to be replaced by cooler denser water and the entire pot eventually reaches a boiling point.
- heater- the air closest to the heater is warmed up first, which is replaced by cooler air. This creates a convection current, distributing the heat throughout the room.
- hot air balloon- the air inside the balloon becomes less dense as it rises, lifting the balloon along with it.
what is radiation?
- refers to the transfer of heat in the form of electromagnetic waves.
- unlike conduction and convection, which involve the transfer of heat through direct contact or the movement of fluids, radiation can occur in a vacuum or through transparent mediums.
examples of radiation (transfers from what to what)?
- sun’s heat- the sun emits electromagnetic radiation, including visible light and infrared radiation. earth absorbs this radiation, and the absorbed energy is transformed into heat, warming the earth’s surface.
- microwave- microwaves use electromagnetic radiation to heat food. The microwaves cause water molecules in the food to absorb the radiation, generating heat and cooking the food.
what is useful and wasted energy used to describe?
useful (intended output) and wasted (unintended output) energy is used to describe the effectiveness or utility of energy in a particular context.
examples of useful energy (and why)?
- incandescent light bulbs- electrical energy is converted into visible light energy, which is the useful energy that illuminates a room.
- car engine- chemical potential energy in the fuel is converted into mechanical energy that propels the vehicle.
- kettle- electrical energy from the power source is converted into heat energy, which is the useful energy boiling the water.
examples of wasted energy (and why)?
- incandescent light bulbs- incandescent bulbs also emit a significant portion of their energy as heat, which in terms of lighting, often considered waste.
- car engine- in many mechanical systems, such as engines, friction between moving parts generates heat that is often considered wasted energy. Lubrication (oil) is used to minimise this effect and improve efficiency.
- kettle- kettles also emit sound energy which in this context is a form of waste energy.
how to calculate energy efficiency (formula + units)?
energy efficiency (%) = relevant or intended energy (j)/total energy used (j) x 100
