2.3 Conduction, Convection, & Radiation Flashcards
What is conduction?
Where vibrating particles transfer energy to neighbouring particles
Describe how a flame could heat up a piece of metal
Imagining the piece of metal as a series of particles, as the end of the metal is heated, energy is transferred to the metal (to the kinetic energy store of the particles at that end) which causes the particles to vibrate faster and so they collide with their neighbouring particles more often and with more energy. As the collisions transfer kinetic energy, the neighbours will also vibrate faster and collide more with their neighbours. As this repeats, energy is passed along the sheet of metal until the heat is spread out evenly.
What is ‘thermal conductivity’?
How well objects transfer energy by conduction
What has a high thermal conductivity?
Metals
What has a low thermal conductivity?
Plastics
What does convection occur in?
Liquids and gases
Describe what convection is
As the particles in fluids aren’t fixed, once they’re heated and gain kinetic energy, they all move around faster. Via the process of diffusion, this will cause the more energetic particles to move away from the warmer region towards the cooler region. Overall, this means the higher energy particles in the warmer region are a lot more spread out than those in the cooler region so effectively the fluid in the warmer region expands as it heats up, so becomes less dense than the cooler region.
Describe how convection would take place in a container of fluid (liquid or gas)
As we heat the container, the particles near the heat source would gain kinetic energy and spread out, becoming less dense. As they are less dense, these particles would rise above the colder, less dense particles above them and at the same time these cooler particles would sink down and take their place. Whilst this is happening, the hot particles would lose their energy and cool down, and the cool particles and the bottom would heat up; because of this, the cycle would continue for as long as the fluid is being heated. We call this cycle a ‘convection current’.
What is the cycle of convection called?
Convection current
Where can a convection current be seen in a house?
Through the use of radiators
How do we reduce convection?
By stopping the free flow of fluids, e.g. a blanket
What is the difference between conduction and convection?
In conduction, only the energy is transferred and in convection, the particles move.
How can heat energy be transferred without particles?
- It can travel through a vacuum. This happens when energy is transferred by radiation (infrared waves). All objects constantly absorb and emit radiation. Importantly, the hotter an object is, the more radiation it emits.
What do we mean by the term ‘fluid’, and which states of matter are considered fluids?
A fluid is a substance in which the particles are free to move around. They include both liquids and gases.
