Physics --> Chapter 1.5 Flashcards
What is heat
Heat is a form of energy
What is temperature? What happens to an object when it is heated?
Temperature is the degree of hotness or coldness. When heat is applied/given to an object, the following things happen:
1. the object gets hotter because there is an increase in the temperature
2. There is a change of state
3. There is an increase in size (expansion)
What is expansion
It is the increase of size in all directions when heated
What is contraction
It is the decrease in size in all directions when cooled
How does matter expand?
When an object is heated, its temperature rises and the molecules in it start to vibrate rapidly because they gain energy and start to push each other. In other words, they need more space to move about. This causes an increase in size of the object and we say that it expands
How does matter contract?
When an object is cooled, its temperature falls and the molecules start to move slowly because they lose energy. They come closer to each other. In other words, the molecules need less space to move about. As a result, there is a decrease in size and we say that it contracts.
Why are there gaps kept in between railway tracks
to allow for expansion to take place when heated
_______ expand the least. _____ expand the most.
Solids. Gases
Explain irregular expansion of water
Most liquids expand when heated and contract when cooled. Water is an exception. From 4 degrees Celsius to 100 degrees Celsius, water behaves normally. However from 0 degrees celsius to 4 degrees celsius the unusual behaviour in water takes place.
Why does ice float on water?
When water freezes to change to ice at 0 degrees celsius, it expands or increases its volume. Density decreases as volume increases (d = m/v). Since ice takes up more spaces than water, it becomes less dense so the ice floats on water. The warm water at 4 degrees celsius stays at the bottom.
What are the freezing and boiling points of the different liquids used in thermometers?
The freezing point for mercury is - 39 degrees celsius and the boiling point is 360 degrees celsius. The freezing point of alcohol is -115 degrees celsius and the boiling point is 78 degrees celsius.
What are the advantages and disadvantages of a mercury thermometer?
MERCURY THERMOMETER
Advantage - Mercury expands evenly as it gets warmer and can be used to measure very high temperatures up to 360 degrees celsius
Disadvantage - However, this thermometer cannot be used to measure very low/cold temperatures (such as in cold areas like the North Pole) because it freezes at - 39 degrees celsius.
What are the advantages and disadvantages of an alcohol thermometer?
ALCOHOL THERMOMETER
Advantage - It expands more evenly than mercury and can be used to measure very cold temperatures because its freezing point is -115 degrees celsius.
Disadvantage - Alcohol thermometers cannot be used to measure very hot temperatures as it has a boiling point of 78 degrees celsius.
Explain the process of the irregular expansion of water (hot)
From 0 degrees to 4 degrees C the temperature rises. The water contracts instead of expanding. Thus, the volume decreases and the density increases (because d = m/v). Water has a maximum density of 4 degrees C
Explain the process of the irregular expansion of water (cool)
Lesson 32 in copy
When water goes from 4 * to 0 * C the temperature falls. The water expands instead of contracting. Thus, the volume increases and the density decreases (because d = m/v).
(See Lesson 32 in copy)
