Questions Flashcards
Explain the difference between heat, temperature and thermal energy
Heat is the transfer of energy from a hotter to cooler object until thermal equilibrium reached. Temperature is the average kinetic energy of particles in an object. Thermal energy is the sum of potential and kinetic energy of particles.
On a hot, dry day your body sweats to cool you. Explain how sweating cools the body
Sweat places layer of water on skin. Water evaporates which is a phase change. Phase change needs latent heat which it takes from body. Removal of energy from body cools it.
Tiled floors often feel colder to walk on than carpeted floors even if the two are at the same temperature.
The carpet is a poor conductor. The tiles, on the other hand, are good conductors of heat. When your feet are on the tiles, the heat goes into the tile and is conducted away from the surface. This transfer continues until the tile and your feet reach the same temperature, which is much lower than the initial temperature of your feet so your feet feel cold.
While Belinda was working in the study, she noticed that her feet were hot. Looking down she realised that the sun was coming through the window onto her feet. Explain how the sun heats her feet.
Radiation, heat energy in electromagnetic waves from sun. Wave pass through transparent objects like glass and hit feet. Kinetic energy of skin cells increases as radiation causes cells to increase vibrations. As temperature is measure of average kinetic energy and kinetic energy has increases, feet increase in temperature and feel hotter.
When you go swimming in a still lake after a hot, sunny day, you will often notice that the surface of the water is warm but the deeper the water, the colder it gets. Explain this observation.
The water near the surface is heated directly by the Sun’s radiation. When the water is warmed it becomes less dense and therefore floats on the more dense unheated water below it. There will thus be no convectional mixing and if the water is still the only method of heat transfer to the deeper water will be by conduction, which will be slow because water is a poor conductor.
In winter, birds often fluff up their feathers as they sit on a tree branches. Explain how this helps keeps them warm.
Fluffed feathers trap air next to skin. This restricts heat lost due to conduction as air is a good insulator. Trapped air minimises loss due to convection as restricted air movement. No convection currents.
Cats, kangaroos and other animals frequently lick themselves or pant on hotter days. Explain the process by which this helps to keep them cool.
Water on skin evaporates. Evaporation is a change of phase requiring energy. Energy taken from licked areas reduces temperature, resulting in reduced body temp.
If you accidentally hold your hand in front of a boiling kettle you can receive a severe burn. If however you splash your hand with the boiling water, you will not be burnt as severely. Explain this observation assuming that a similar mass of boiling water and steam.
Both get the same burn from boiling water cooling. Burn from kettle requires water to condense then cool. Therefore it receives more energy to burn skin.
Does a block of ice have any heat energy?. Explain you answer in terms of the kinetic theory.
Thermal energy is the sum of kinetic/potential energy in a object. All matter is made up of particles in constant motion. In ice, a solid, the particles are in fixed positions but they vibrate. Since they move, they have kinetic energy. Since theres a small distance apart, they have potential energy. So they have heat energy.
What is 298K in the Celsius scale of temperature?
298 - 273.15 = 24.85°C
Explain why the temperature of a landmass changes more from day to night than the water surrounding it.
Water has a higher specific heat capacity than the landmass. So it takes longer to lose heat compared to landmass.
