Heating and cooling curves and latent heatIB MYP Physics: Subtopic test

1. 1
   A student heats a beaker containing 0.20 kg of ice at −10 °C using an electric heater that supplies energy at a constant rate. She records the temperature every minute. The temperature rises to 0 °C in the first 30 seconds, stays at 0 °C for the next 8 minutes while the ice melts, then rises steadily to 100 °C over the next 10 minutes, and stays at 100 °C while the water boils.

   (a)

   Which change is happening while the temperature stays at 100 °C?

   [1 mark]

   • AIce is melting to form water
   • BLiquid water is changing to steam
   • CSteam is being heated to a higher temperature
   • DSteam is condensing to form liquid water

   (b)

   What happens to the energy supplied during the flat section at 0 °C?

   [1 mark]

   • AIt increases the average kinetic energy of the particles
   • BIt is all transferred to the surroundings
   • CIt is used to heat up the thermometer
   • DIt changes the arrangement of the particles as the ice melts

   (c)

   Explain why the temperature stays at 0 °C while the ice melts, even though the heater continues to supply energy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In many hot countries, people store drinking water in porous clay pots. Water slowly seeps through the pot to its outer surface and evaporates there. Even on a very hot day, the water inside the pot stays cooler than the air outside.

   (a)

   Which statement correctly describes evaporation?

   [1 mark]

   • AIt happens only at the boiling point, throughout the liquid
   • BIt is when a gas changes to a liquid on a cool surface
   • CIt happens at any temperature below the boiling point, at the surface of a liquid
   • DIt happens only when the liquid is heated above 100 °C

   (b)

   Which particles are most likely to escape from the surface of a liquid during evaporation?

   [1 mark]

   • AThe fastest-moving particles near the surface
   • BThe slowest-moving particles near the surface
   • CAll the particles in the liquid, equally
   • DParticles from the bottom of the liquid

   (c)

   Explain why evaporation cools the water inside the pot.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student places 0.20 kg of ice at 0 °C in a beaker and heats it with a 500 W heater. All of the heater's energy is transferred to the ice. The specific latent heat of fusion of ice is 334 000 J/kg. The temperature stays at 0 °C until all of the ice has melted.

   (a)

   Calculate the energy needed to melt all of the ice, and the time this takes.

   [3 marks]

   (b)

   The student continues to heat the water after all of the ice has melted until the water boils. Describe how the temperature changes and explain, in terms of particles, why the temperature stays constant once the water starts to boil.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A laundry business in Mumbai dries large numbers of washed cotton sheets on outdoor lines. The owner is considering building a drying room with a heater and a fan. Drying happens because water evaporates from the wet cloth.

   (a)

   Design an investigation to find out how the temperature of the surrounding air affects the rate of evaporation of water from cloth. Include a hypothesis, the variables and a method.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of using a heated drying room with a fan instead of outdoor lines, and evaluate which the business should use.

   [6 marks]

   Total for question 4: 12 marks

End of questions