Last Min Revision Flashcards
How does evaporation cools down a liquid?
Evaporation occurs when more energetic particles moving near the surface of the liquid have enough energy to escape. Thus, when the particles with the most energy leaves, the average kinetic energy of the liquid is reduced (reduce in temperature).
Also, for the water to evaporate it require latent heat to undergo a phase change from liquid to gas. This requires a large amount of heat energy known as latent heat of vaporization. Which means heat leaves the system as the steam carries the energy with them, cooling down the system.
If they say calculate the force of gravity?
Its asking about weight
Define Mass and Weight?
Mass is the amount of matter an object is made up of, it is measured in kg. While, weight is a downward force due to gravity an object experiences due to its mass. Thus, the mass does not change when the location changes (different gravitational field) but the weight does due to change in gravitational field because W= mg.
Define friction
Friction is a force that opposes motion. If an object has no motion then there is no friction.
Friction occurs when one surface moves against the other, the movement causes kinetic energy to be changed into heat and sound energy.
We can reduce friction by lubrication.
What is inversely proportional and directly proportional?
Inversely proportional is when one value increases the other value decreases.
Directly proportional is when both values increase or decrease together.
Explain the effect on Work and Power if the object mass increase but the speed and distance moved is the same.
Work is the energy transferred to or from an object due to a force moving it a distance (parallel displacement)
W= Fd
Since, the mass increase it means the weight (Force) will increase because weight equals to mass time gravity. Assuming the distance remained the same, then an increase in the force increases work because they are directly proportional.
Power is the rate at which work is done. Since power equals to change in energy divide by time. Assuming the time remain constant, increasing work increase power because work and power are directly proportional.
What are some modification you can do to reduce the rate of heat transfer?
- Add light, shiny surface to reduce radiation. This is because dark, Matt surfaces are good absorbers and emitters of infrared radiation, while light shiny surface like silver are bad absorbers and emitters of infrared radition as they are good thermal reflectors. Which means the radiation is reflected/ bounced back.
- Add vacuum as it reduce heat transfer by conduction and convection. This is because a vacuum is space without matter. This means neither conduction or convection cannot happen as both need a medium to transfer the thermal energy.
- Increase the thickness of the insulator, reduce the rate of cooling/heating. By increasing the thickness of the insulator becomes more efficient in preventing heat from flowing through.
What is an insulator?
An insulator is an material that does not allow heat to pass through. It has low thermal conductivity and does not transfer heat efficiently and quickly.
Explain convection in detail.
convection is the heat transfer in fluids due to convection current. This is when the warmer fluid particles (gas or liquid) gains more kinetic energy which cause them to move faster and further away from each other, causing the average distance between the particles to increase, so they become less dense and rise. While the colder fluid particles have less kinetic energy and the particles come closer together, becoming more dense so they sink. This creates a convection current.
Warmer fluids become less dense because density is a measure of the mass a substance has per unit of volume. Thus, since warmer fluids average distance between the particles increase, it has less particles taking up a larger volume which means less mass per unit volume.
What is thermal expansion?
Thermal expansion is when matter is heated they expand, causing it to increase in length or size. This happens because when the object is heated its particles gains more kinetic energy and move faster and further apart from each other, causing the average distance between the particles to increase. This means now the particles takes up more space, causing the object to expand in size or length. This lead to increase in volume.
Describe the reasons for energy lost (heat)
Energy can be lost due to the transfer or heat (thermal) of heat energy to the surrounding by conduction, convection and radiation.
For instance:
- Conduction through walls, ceiling, floor, windows, air frames.
- Convection through gaps in doors and windows.
- Radiation through the walls and surfaces including windows.
What is humidity?
Humidity is a measure of how much water vapor is in the air. As humidity increase, the rate of evaporation decrease.
