GCSE Physics: P2 - Energy transfer by heating

What is specific heat capacity?

the amount of energy required to raise the temperature of 1 kg of a substance by 1 *C

What is the equation for specific heat capacity

🛆E = m X c X 🛆ϴ

change in thermal energy (J) = mass (kg) X specific heat capacity (J/kg C) X temperature change (C)

Calculate the energy required to increase the the temperature of 2 kg of water from 20C to 100C. The specific heat capacity of water is 4200 J/kg *C.

🛆E = m X c X 🛆ϴ

🛆E = 2 kg X 4200 J/kgC X 80C

🛆E = 672000 J

= 672 kJ

A hot water bottle cools down from 80C to 20C, releasing 756 000 J of thermal energy. Calculate the mass of the water in the hot water bottle. The specific heat capacity of water is 4200 J/kg*C

🛆E = m X c X 🛆ϴ

756 000 J = m X 4200 J/kgC X 60C

756 000 J / = m (kg)

4200 J/kgC X 60C

m = 3 kg

What is thermal conductivity?

a measure of how well a material conducts energy when it is heated.

The higher the thermal conductivity of a material...

the higher the rate of energy transfer by conduction across that material

How do builders construct walls in order to insulate a building?

- in order to insulate buildings

- builders pack the cavity between the internal breezeblock wall and the external brick wall

- with an insulating material that has a very low thermal conductivity

- so less thermal energy can escape the house

How is thermal energy prevented from escaping the windows of a building?

- most buildings use double-glazed windows because they have low thermal conductivity

- so less thermal energy can escape the building

If a building has high thermal conductivity...

more thermal energy can escape the house

If a building has low thermal conductivity....

less thermal energy can escape the house

How is thermal energy prevented from escaping the loft of a building?

- loft insulation ensures less thermal energy can escape the building because loft insulation has low thermal conductivity

How can we reduce thermal energy transfer from a house?

- construct the building using insulating materials with a low thermal conductivity

- so less thermal energy can escape the house

- build the house with thick walls

- as this reduces the rate of thermal energy transfer

What is the aim of Required Practical 1 : Specific Heat Capacity

Aim: To determine the specific heat capacity of a material

Required Practical 1: Specific Heat Capacity

Describe the steps involved in a practical investigating the specific heat capacity of a material

1) Add the material to a beaker on a balance and determine its mass

2) Place a thermometer and an immersion heater into the material

3) Record starting temperature of the material

4) Wrap the beaker in insulating foam to reduce thermal energy transfer to the surroundings

5) Connect a joulemeter to the immersion heater

6) Connect a powerpack to the joulemeter

7) Set a timer for 30 minutes

8) Record the number of joules of energy that passed into the immersion heater

9) Record the final temperature of the material

10) Using the values recorded for mass, temperature change and change in thermal energy, calculate the specific heat capacity of the material in J/kg*C

What possible inaccuracies could occur during a practical investigating the specific heat capacity of a material and how can we prevent them?

- the value for specific heat capacity could be inaccurate due to thermal energy passing out of the beaker and into the air

- we can reduce this by using an insulator with a lower thermal conductivity

- the value for specific heat capacity could be inaccurate if not all thermal energy has passed into the material

- we can overcome this by ensuring that the immersion heater is fully submerged in the material

- the value for specific heat capacity could be inaccurate if there is an incorrect reading of the thermometer

- we can prevent this by using an electronic temperature probe

- the value for specific heat capacity could be inaccurate if the thermal energy is not spread throughout the entire material

- we can prevent this by stirring the material around

Required Practical 2 : Thermal Insulators

Describe the steps involved in a practical investigating the effectiveness of thermal insulators

1) Place a small beaker inside a large beaker

2) Use a kettle to boil some water

3) Transfer 80 cm^3 of hot water into the small beaker

4) Use a piece of cardboard as a lid for the large beaker

5) Place a thermometer through a hole in the lid and into the hot water

6) Record the starting temperature of the water and begin a stopwatch

7) Record the temperature of the water every 3 minutes for 15 minutes

8) Repeat the practical using the same volume of water

9) However, use an insulating material (e.g. bubble wrap) to fill the gap between the two beakers this time

10) Repeat the practical a few more times in order to test a range of different insulating materials (e.g. cotton wool, polystyrene balls)

Describe the variables involved in a practical investigating the effectiveness of thermal insulators

Independent variable - the type of insulating material

Dependent variable - the temperature of the water

Control variables - the volume of the water, the mass of the insulating material, the starting temperature of the water

Describe the results of a practical investigating the effectiveness of thermal insulators

- we can record the results of the practical in a table

- and then plot cooling curves for the different insulators

- from these cooling curves, we will be able to observe that the water will cool down most slowly when the most effective insulating material is being used

Required Practical 2 : Thermal Insulators

Describe the steps involved in a practical investigating how the thickness of a material affects the thermal insulation

1) Use measuring cylinder to measure volume of water

2) Set up a beaker containing 80 cm^3 of hot water boiled using a kettle

3) Measure the starting temperature using a thermometer

4) Using a thermometer, measure the temperature of the water every 3 minutes for 15 minutes

5) Repeat the experiment but wrap 2 layers of newspaper around the beaker this time

6) Repeat the experiment 2 more times using 4 layers and then 6 layers of newspaper

7) When repeating the experiment with a different number of layers, the same starting temperature of the water and volume of water should be used

8) Plot a cooling curve to show the more layers, the slower the water will cool down

Describe the variables involved in a practical investigating how the thickness of a material affects the thermal insulation

Independent variable - the number of layers of newspaper

Dependent variable - the temperature of the water

Control variables - the starting temperature of the water, the volume of the water

Describe the results of a practical investigating how the thickness of a material affects the thermal insulation

- we can plot a cooling curve to show our results

- the cooling curve will show that: the more layers of newspaper, the slower the water cools down

- having more layers of newspaper is a more effective thermal insulator than having fewer layers