Kinetic theory and gas behaviourIB MYP Physics: Subtopic test

1. 1
   A cyclist in Amsterdam leaves a sealed bicycle tyre in the sun. The volume of the tyre stays the same, but the temperature of the air inside it rises from 15 °C to 45 °C.

   (a)

   What causes the pressure of the air on the inside walls of the tyre?

   [1 mark]

   • AThe weight of the air particles pressing down
   • BCollisions of moving air particles with the walls
   • CAir particles sticking to the walls
   • DThe air particles expanding when heated

   (b)

   What is 45 °C in kelvin?

   [1 mark]

   • A318 K
   • B273 K
   • C45 K
   • D-228 K

   (c)

   Explain why the pressure inside the tyre rises as the temperature rises.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A bicycle pump contains 120 cm³ of air at a pressure of 100 kPa. The outlet is blocked, and the piston is pushed in slowly until the air occupies 40 cm³. The pump is pushed in slowly, so the temperature of the air stays constant.

   (a)

   What is the pressure of the air when the volume is 40 cm³?

   [1 mark]

   • A33 kPa
   • B40 kPa
   • C300 kPa
   • D12 000 kPa

   (b)

   Which statement explains the change in pressure?

   [1 mark]

   • AThe particles move faster so they hit the walls harder
   • BThe particles become heavier
   • CThere are more particles in the pump
   • DThe particles hit the walls more often because they are in a smaller space

   (c)

   The piston is pushed in further, until the volume is 30 cm³. Calculate the new pressure.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A class in Auckland investigates how the pressure of a fixed mass of air changes with its temperature. Air is sealed in a rigid flask connected to a pressure gauge, and the flask is heated in a water bath. The pressure is 100 kPa at 20 °C, 107 kPa at 40 °C, 114 kPa at 60 °C and 121 kPa at 80 °C.

   (a)

   State a testable hypothesis for this investigation and give a scientific reason for it.

   [3 marks]

   (b)

   Describe the trend in the results and convert the lowest and highest temperatures to kelvin.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A family in Mumbai uses a pressure cooker. When the lid is sealed, steam cannot escape, so the pressure inside rises and the water boils at about 120 °C instead of 100 °C. The food cooks faster. A safety valve opens if the pressure becomes too high.

   (a)

   Explain, using kinetic theory, why the pressure inside the sealed cooker rises as it is heated.

   [6 marks]

   (b)

   Discuss whether pressure cookers should be recommended to families who cook every day.

   [6 marks]

   Total for question 4: 12 marks

End of questions