Thermal Properties & Temperature (Cambridge O Level Physics)

State three factors that determine the rate of evaporation of water.

A person climbs out of a swimming pool and stands in the open air.

Explain why the evaporation of water from the surface of the person’s body causes the person to feel cold.

The arrows on Fig. 5.1 represent changes of state.

One of the arrows is labelled. Label each of the other arrows with the correct change of state. Write the change of state on the dotted lines next to each arrow.

A beaker contains some liquid with a low boiling point. The beaker is placed onto a small amount of water, as shown in Fig. 5.2.

The liquid in the beaker evaporates quickly. The water on the bench cools and turns to ice.

Explain why the water cools.

In a laboratory at normal room temperature, 200 g of water is poured into a beaker. A thermometer placed in the water has a reading of 22 °C.

Small pieces of ice at 0 °C are added to the water one by one. The mixture is stirred after each addition until the ice has melted. This process is continued until the temperature recorded by the thermometer is 0 °C.

The total mass of ice added to the water is found to be 60 g.

The specific heat capacity of water is 4.2J/(g °C).

Calculate the energy transferred from the water's thermal energy store originally in the beaker.

thermal energy = ...........................................................

Fig. 5.1 shows a plastic cup. The cup contains sand, an electric heater and a thermometer.

The power of the heater is 50 W. The mass of the sand in the cup is 550 g. The initial temperature of the sand is 20 °C. The heater is switched on for 2.0 minutes.

The temperature is recorded until the temperature stops increasing. The highest temperature recorded by the thermometer is 33 °C.

On a sunny day, the temperature of the sand on a beach is much higher than the temperature of the sea.

 
Explain why.

Fig. 4.1 shows apparatus used by a student to measure the specific heat capacity of iron.

The student improves the accuracy of the experiment by placing material around the block, as shown in Fig. 4.2.

The current in the heater is 3.8 A and the potential difference (p.d.) across it is 12 V. The iron block has a mass of 2.0 kg. When the heater is switched on for 10 minutes, the temperature of the block rises from 25 °C to 55 °C.

Calculate the specific heat capacity of iron.

specific heat capacity = ...........................................................

A hot steel rod is cooled by plunging it into cold water, as shown in Fig. 3.1.

Fig 3.1

The steel rod has a mass of 2.0 kg and is initially at a temperature of 500°C. It cools to 50°C when placed in the water.

The specific heat capacity of steel is 460 J /(kg°C).

Calculate the thermal energy (heat) lost by the steel rod as it cools to 50°C.

thermal energy = ......................................................... 

A small mass of water boils when the rod is placed in the water. The remaining water then 
cools to room temperature and some of it evaporates. 

In both boiling and evaporation, water molecules escape into the air.
 

[1]

[2] 

One type of renewable energy source is shown in Fig. 4.1.

Fig. 4.1

State the name of the renewable energy source shown in Fig. 4.1

1000 kg of cold water at a temperature of 20 °C is pumped down to the hot rocks. 
The water returns partly as steam and partly as hot water. 
The steam and the hot water are both at a temperature of 100 °C.

The specific heat capacity of water is 4200 J / (kg °C).

energy = .......................................................  J [2]
 

State and explain any effect on the sensitivity of a liquid-in-glass thermometer of reducing the diameter of the capillary tube.

State and explain any effect on the sensitivity of a liquid-in-glass thermometer of increasing the volume of the liquid-filled bulb.

Gas of mass 0.23 g is trapped in a cylinder by a piston. The gas is at atmospheric pressure which is 1.0 × 10⁵ Pa. Fig. 4.1 shows the piston held in position by a catch.

The volume of the trapped gas is 1.9 × 10^–4 m³.

An electrical heater is used to increase the temperature of the trapped gas by 550 °C.

The specific heat capacity of the gas is 0.72 J / (g °C).

When the temperature of the gas has increased by 550 °C, its pressure is 2.9 × 10⁵ Pa. The catch is then released allowing the piston to move. As the piston moves, the temperature of the gas remains constant.

A beaker contains some water at room temperature. A student places a mercury-in-glass thermometer in the water with the bulb of the thermometer just beneath the surface of the water.

Fig. 4.1 shows the arrangement.

The student uses an electric fan to blow air across the open top of the beaker. She notices that the reading on the thermometer begins to decrease.

Explain, in terms of water molecules, why the temperature of the water at the surface begins to decrease.

The student places the thermometer near the bottom of the beaker. The electric fan continues to blow air across the top of the beaker.

After some time, the student observes that the temperature of the water at the bottom of the beaker is decreasing.

State the name of the thermal transfer method causing this and explain what is happening in the water.

The thermometer used in this experiment has a small range and a large sensitivity.

A group of students were given the equipment shown in Fig. 1.1 and were asked to identify an unknown clear liquid by its specific heat capacity. 

The students were provided with the unknown substance, an electric water bath, and were allowed to use water from the tap.

Suggest why the students were given an electric water bath rather than a Bunsen burner.

List the quantities that the students must measure to determine the specific heat capacity of the unknown liquid.

The students are given Table 1.2 to help with their investigation.

Table 1.2 

Suggest a method for measuring the energy transferred from the water bath to the unknown substance.

The student recorded the following measurements.

The fizz in a soda bottle is caused by carbonation. When the soda is bottled, carbon dioxide is added to the liquid to give it a fizzy taste. The carbon dioxide gas is kept in the liquid by the pressure inside the bottle.

When the bottle of soda is opened, state what happens to the pressure inside the bottle and why.

Fig 1.1

Fig 1.2 shows two mugs of tea, A and B. They both hold the same volume of tea.

Fig 1.2

State from which mug the tea evaporates quicker. Explain why, in terms of the behaviour of molecules and the process of evaporation.