Conduction videos
Video 1: Test on rate of conductions of different metals
This video proves that different materials have different rate of conduction. In the video, the different metals conduct heat from flame to the end of the rod, the wax placed at end of each rod gains heat from the metals and melts. The wax attaching the thumbnail to the copper rod melts the fastest, which proves that copper is better conductor when compared to the other metals. Wax on the steel rod took the longest time to melt, which shows that steel is not a better conductor when compared to other mteals.
This is the conductivity of metals in descending order [better--->good].
Copper, aluminium, bronze, nickel, steel.
Video 2: Test on conduction of wire gauze
This video shows that flame is not able to burn through a wire gauze. As seen, the wire gauze is made of metal, which conducts heat [by molecular vibration & electron diffusion] away from the flame, that is why the flame is not seen burning through the gauze. If gauze is pressed fully down onto the flame, it will extinguish as the wire gauze conducts all the heat away from the flame.
Video 3: Test on conduction of fork [similar to my self made video]
As seen from video, the flame goes off as soon as it comes into contact with the fork. The metal fork is a good conductor of heat. All the heat from the flame is conducted away by the metal fork, which causes the flame to go off.
Showing posts with label Conduction. Show all posts
Showing posts with label Conduction. Show all posts
Thursday, June 25, 2009
Tuesday, June 9, 2009
Conduction
Definition:
It is the transfer of thermal energy through a medium, without medium moving.
1) Heat supplies thermal energy to particles
2) Thermal energy is transferred from one particle to another by vibration of particles
3) Thermal energy is converted to kinetic energy
4) Kinetic energy of vibrating particles at hot end is transferred to neighbouring particles
Free electron diffusion
1) Only conductors contain free electrons
2) Thermal energy in heat converted to kinetic energy
3) Free electrons gain kinetic energy and move faster
4) Electrons diffuse into cool end
5) Electrons collide with particles and transfer kinetic energy into them
Conduction in liquids and gases
Liquids and gases are POOR conductors of heat.
As shown, water at the top of test tube boils, but ice remains. The rate of heat transfer from top to bottom is extremely slow as water is a poor conductor. Hence, ice melts extremely slowly.
Bunsen burner does not light up match when it is placed a distance away from Bunsen burner, hence air is a poor conductor. The rate of heat transfer from flame to the match is extremely slow. Heat is trasnferred by conduction and also radiation.
Which is a poorer conductor? Air or Water?
Air.
In air, particles are spaced further apart than those in solids. Collisions between molecules are less frequent in liquids, lesser in gases. Transfer of kinetic energy from fast-moving particles to neighbouring particles is slower.
Applications of conduction
1) Cooking utensils made of metals (eg. aluminium, stainless steel) are able to conduct heat and cook food faster.
2) Soldering iron rods are made of iron with tip made of copper. Copper is a much better conductor of heat than iron
Insulators
1) Wool is used as winter clothings. Wool, being an insulator, cause heat to be trapped in wool, unable to get out of wool, keeps body warm.
2) Handles of cooking utensils made of insulators so that hand will not get scalded while using it.
Definition:
It is the transfer of thermal energy through a medium, without medium moving.
- Main mode of heat transfer in solids, also occur in liquids and gases.
- Conductors: Metals (eg. Silver, gold, copper, brass)
- Insulators (poor conductors): Glass, rubber, plastic, wood, wool, cotton, water, air
- Different materials conduct heat at different rates (depends on whether material is conductor or insulator)
- Molecular vibration
- Free electron diffusion
- slow to transfer thermal energy
- no transfer of particles
- occurs in both conductors and insulators
1) Heat supplies thermal energy to particles
2) Thermal energy is transferred from one particle to another by vibration of particles
3) Thermal energy is converted to kinetic energy
4) Kinetic energy of vibrating particles at hot end is transferred to neighbouring particles
Free electron diffusion
- increase speed of transfer of thermal energy
- involves transfer of particles
- occurs in conductors only
1) Only conductors contain free electrons
2) Thermal energy in heat converted to kinetic energy
3) Free electrons gain kinetic energy and move faster
4) Electrons diffuse into cool end
5) Electrons collide with particles and transfer kinetic energy into them
Conduction in liquids and gases
Liquids and gases are POOR conductors of heat.
As shown, water at the top of test tube boils, but ice remains. The rate of heat transfer from top to bottom is extremely slow as water is a poor conductor. Hence, ice melts extremely slowly.
Bunsen burner does not light up match when it is placed a distance away from Bunsen burner, hence air is a poor conductor. The rate of heat transfer from flame to the match is extremely slow. Heat is trasnferred by conduction and also radiation.
Which is a poorer conductor? Air or Water?
Air.
In air, particles are spaced further apart than those in solids. Collisions between molecules are less frequent in liquids, lesser in gases. Transfer of kinetic energy from fast-moving particles to neighbouring particles is slower.
Applications of conduction
- Conductors
- Insulators
1) Cooking utensils made of metals (eg. aluminium, stainless steel) are able to conduct heat and cook food faster.
2) Soldering iron rods are made of iron with tip made of copper. Copper is a much better conductor of heat than iron
Insulators
1) Wool is used as winter clothings. Wool, being an insulator, cause heat to be trapped in wool, unable to get out of wool, keeps body warm.
2) Handles of cooking utensils made of insulators so that hand will not get scalded while using it.
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