P1 - Heat Transfer Flashcards
What are the 3 ways that heat energy can be transferred?
Radiation, conduction and convection
What is heat radiation?
The transfer of heat energy by infrared radiation
Which states of matter does conduction occur in?
Solids
Which states of matter does convection occur in?
Liquids and gases
How does temperature difference affect transfer of energy by heating?
The larger the temperature difference between a body and its surroundings, the faster energy is transferred by heating
How does surface area affect infrared radiation?
The larger the surface area, the higher the rate of infrared radiation because there are more places that the waves are emitted from
In terms of heat radiation, what happens when an object is hotter than its surroundings?
The object emits more radiation than it absorbes as it cools
In terms of heat radiation, what happens when the object is cooler than its surroundings?
It absorbs more radiation than it emits as it warms up
How does the surface type of the object affect its radiation?
Dark, matte surfaces absorb and emit much more infrared radiation than shiny, light surfaces
Why don’t shiny, light surfaces absorb as much infrared radiation?
They reflect off most of the waves
Describe how solar hot water panels make use of our knowledge of surface types and radiation
They contains water pipes under a black surface to heat the water in the pipes
Radiation from the Sun is absorbed by the black surface to heat the water in the pipes
Describe the arrangement, forces and energy in solids
Strong forces of attraction hold the particles in a fixed regular arrangement
The particles don’t have much energy so that can only vibrate about their fixed positions
Describe the arrangement, forces and energy in liquids
The forces of attraction are weaker so the particles are still close together but they can move past each other
The particles have more energy than in a solid so they move in random directions at low speeds
Describe the arrangement, forces and energy in gases
Almost no forces of attraction
Particles have more energy than in liquids and solids and are free to move in random directions at high speeds
What happens to the particles of an object when you heat it?
The particles get more kinetic energy and vibrate or move faster
What is conduction?
The process where vibrating particles pass on their extra kinetic energy to neighbouring particles
This causes heat to spread throughout a solid
What factor affects the rate of conduction?
If the particles are closer together, the particles will collide more often and the rate of conduction will be higher
What makes a material an insulator?
When the material has larger spaces between its particles
What causes metals to be good conductors?
Their free electrons can easily collide with each other and pass on the kinetic energy
What is kinetic theory?
The theory that describes how particles move in solids, liquids and gases and tells us that the energy of a particle is its movement or vibration (kinetic energy)
What is convection?
The process where more energetic particles move from the hotter region to the cooler region and take their heat energy with them
Describe the convection in an immersion heater
Heat is transferred from the heater coils to the water by conduction (particle collisions)
The particles near the coils get more energy so they move around faster meaning there is more distance between them meaning that this water becomes less dense
The hotter water rises because it is less dense and displaced the colder water out of the way towards the heater coils
The cold water is heated by the coils and the hot water cools at the top of the immersion heater
This circuit repeats over and over again
What is a convection current?
The way that, in convection, the hot water rises becomes cold and sinks and heats again and this circuits repeats again and again
How does surface area affect the rate of heat energy transfer?
Heat is radiated from the surface of an object so the larger the surface area, the more infrared waves can be emitted from the object
How does volume affect rate of heat energy transfer?
If 2 objects at the same temperature have the same surface area but different volumes, the object with the smaller volume will cool quicker
This is because a higher proportion of the object will be in contact with its surroundings
How does the type of material affect the rate of heat energy transfer?
Conductors transfer heat much faster than insulators
If an object is in contact with a conductor, the heat will be conducted away much faster than if the object was in contact with an insulator
How do vaccum flasks prevent heat transfer?
The glass bottle is double-walled with a vaccum between the 2 walls preventing all conduction and convectiom through the sides
The bottle is supported with insulating foam minimising conduction to or from the outer glass bottle
The stopper is made of plastic and filled with cork or foam to reduce heat conduction
What is the simplest way that animals have evolved to deal with heat transfer?
Arctic foxes have small ears to prevent heat loss by radiation
Desert foxes have large ears that allow them to easily lose heat to keep them cool
