Question
In an experiment, smoke particles are suspended in air and viewed through a microscope.
The smoke particles move about with short random movements. Which of the following statements is correct?
Air particles have large masses compared to smoke particles and they move in one direction only.
Air particles have large masses compared to smoke particles and they move in random directions.
Air particles move at high speeds compared to smoke particles and they move in one direction only.
Air particles move at high speeds compared to smoke particles and they move in random directions.
A beaker of liquid is heated slowly so that the liquid evaporates.
During evaporation, from where do the more energetic molecules leave the liquid?
Answer/Explanation
Ans: A
Question
When a liquid evaporates, some molecules escape. The temperature of the remaining liquid changes.
What is the effect on the temperature and from where do the molecules escape?
| temperature of liquid | molecules escape from |
A | decreases | everywhere within the liquid |
B | decreases | the surface only |
C | increases | everywhere within the liquid |
D | increases | the surface only |
Answer/Explanation
Ans: B
Question
A student measures the mass of warm water in an open container over two minutes. The container is kept at a constant temperature. The results are in the table.
time / minutes | mass / g |
0.0 | 33.9 |
0.5 | 30.6 |
1.0 | 27.6 |
1.5 | 24.9 |
2.0 | 22.5 |
Why does the mass of the water change?
The water evaporates.
The water freezes.
The water condenses.
The water boils.
Answer/Explanation
Ans: A
Question
On a warm day, a carton of fresh milk is covered with a wet cloth.
Why does this help to reduce the temperature of the milk?
Some water evaporates from the cloth so the remaining water becomes cooler.
The water has a very high thermal capacity.
The water insulates the milk from the warm air around it.
Water is always colder than the air around it.
Answer/Explanation
Ans: A
Question
A student is investigating evaporation. She soaks a piece of cotton wool in a liquid and attaches
this to the bulb of a thermometer.
As the liquid evaporates the temperature reading on the thermometer changes.
Which statement is correct?
A The more energetic molecules leave the liquid and the temperature reading decreases.
B The more energetic molecules leave the liquid and the temperature reading increases.
C The less energetic molecules leave the liquid and the temperature reading decreases.
D The less energetic molecules leave the liquid and the temperature reading increases.
Answer/Explanation
Ans: A