MEASUREMENT OF THERMAL ENERGY
- When hot water is poured to put off the fire, some hot water dropped to the people and caused less burning compared to that was caused by vapour. Explain why vapour caused severe burning.
[Show answer]Vapour caused severe burning because it contain large amount of heat (Latent heat of vaporization) which is greater than the hot water which is at boiling point.
- Explain why a drop of
methylated spirit placed at the back of hand feels much colder than a drop of
distilled water at the same temperature.
[Show answer]Methylated spirit evaporates more quickly than water. When it evaporates draws heat from your body skin making hand to cool.
- Use your Physics knowledge to answer the following;
-
When we take exercise we sweat. Even on a warm day having wet skin can soon make you feel cold. Why does sweating help us stay cool?
[Show answer]Sweating cools us through evaporation.
When sweat evaporates from the skin, it requires heat energy (from your body) to change from liquid to vapour. As the sweat absorbs this heat and evaporates, your body loses heat, making you feel cooler. -
Even on a warm day having wet skin can soon make you feel cold. Explain why.
[Show answer]Water on the skin evaporates continuously.
During evaporation, the water draws heat from your skin causing your body temperature to fall slightly, making you feel cold.
-
When we take exercise we sweat. Even on a warm day having wet skin can soon make you feel cold. Why does sweating help us stay cool?
- Animals that live in extreme climates have adapted to control their rate of heat transfer. For example, animals in hot climates often have larger ears than those that live in cold climates.
- Explain how having large ears could be an advantages to an animal living in a hot climate.
- In hot conditions, many animals sweat. Explain, in terms of energies, how sweating will help keep an animal cool
- When a drop of ether is placed on the skin, the skin feels cold. Explain why.
[Show answer]Ether evaporates very quickly.
During quick evaporation, ether needs energy (from your skin) to change it into vapour. The heat loss causes temperature of the skin to decrease, making it feel cold. - An ice cube at a temperature of 0°C is more effective in cooling a drink than the same mass of water at 0°C
[Show answer]An ice cube at 0°C absorbs a lot of heat from the drink just to melt (to change ice to water), without its temperature rising but the same mass of water at 0°C does not need to melt, so it absorbs much less heat as it warms.
- A solid is heated at a constant rate until it become a gas. Figure below shows how temperature of the substance increases with time.
- Explain why the temperature of the substance remains constant over the periods
- At what temperature does the substance melt?
- Explain briefly five (5) factors affecting evaporation of liquid
[Show answer]
- Temperature
- Higher temperature → faster evaporation
- Surface Area
- Larger surface area → faster evaporation
- Humidity of the Air
- Higher humidity → slower evaporation
- Lower humidity → faster evaporation
- Wind (Air Movement)
- More wind → faster evaporation
- Nature of the Liquid
- Weaker intermolecular forces → faster evaporation
Higher temperature gives particles more kinetic energy, allowing more of them to escape from the liquid surface.
A larger surface area exposes more molecules to the air.
If the air already contains a lot of water vapour (high humidity), fewer liquid molecules can escape.
Moving air carries away vapour particles from above the liquid surface, allowing more molecules to evaporate.
Some liquids have weaker intermolecular forces and evaporate more easily such as alcohol, petrol.
No comments:
Post a Comment