A rubber balloon is inflated with helium and sealed so that no helium escapes. The balloon is positioned immediately below the ceiling in a room. Heaters are switched on and the temperature of the air in the room increases. The temperature of the helium in the balloon increases and as the rubber stretches, the volume occupied by the helium increases. As the rubber stretches and the volume of the helium increases, the pressure of the helium remains constant. Explain, in terms of the particles of helium, how the pressure of the helium remains constant.

Physics

IGCSE&ALevel

CAIE

Exam No：0625_s23_qp_41 Year：2023 Question No：3(b)(ii)

Answer:

Knowledge points:

2.1.1.1 Know the distinguishing properties of solids, liquids and gases

2.1.1.2 Know the terms for the changes in state between solids, liquids and gases (gas to solid and solid to gas transfers are not required)

2.1.2.1 Describe the particle structure of solids, liquids and gases in terms of the arrangement, separation and motion of the particles, and represent these states using simple particle diagrams

2.1.2.2 Describe the relationship between the motion of particles and temperature, including the idea that there is a lowest possible temperature (−273 °C), known as absolute zero, where the particles have least kinetic energy

2.1.2.3 Describe the pressure and the changes in pressure of a gas in terms of the motion of its particles and their collisions with a surface

2.1.2.4 Know that the random motion of microscopic particles in a suspension is evidence for the kinetic particle model of matter

2.1.2.5 Describe and explain this motion (sometimes known as Brownian motion) in terms of random collisions between the microscopic particles in a suspension and the particles of the gas or liquid

2.1.2.6 Know that the forces and distances between particles (atoms, molecules, ions and electrons) and the motion of the particles affects the properties of solids, liquids and gases

2.1.2.7 Describe the pressure and the changes in pressure of a gas in terms of the forces exerted by particles colliding with surfaces, creating a force per unit area

2.1.2.8 Know that microscopic particles may be moved by collisions with light fast-moving molecules and correctly use the terms atoms or molecules as distinct from microscopic particles

2.1.3.1 Describe evaporation in terms of the escape of more-energetic molecules from the surface of a liquid

2.1.3.1.1 a change of temperature at constant volume

2.1.3.1.2 a change of volume at constant temperature

2.1.3.2 Convert temperatures between kelvin and degrees Celsius; recall and use the equation T (in K) = θ (in °C) + 273

2.1.3.2 Relate evaporation to the consequent cooling of the liquid

2.1.3.3 Recall and use the equation pV = constant for a fixed mass of gas at constant temperature, including a graphical representation of this relationship

2.1.3.3 Demonstrate an understanding of how temperature, surface area and draught over a surface influence evaporation

2.1.3.4 Explain the cooling of a body in contact with an evaporating liquid

2.2.1.1 Describe, qualitatively, the thermal expansion of solids, liquids and gases at constant pressure

2.2.1.2 Describe some of the everyday applications and consequences of thermal expansion

2.2.1.3 Explain, in terms of the motion and arrangement of particles, the relative order of magnitudes of the expansion of solids, liquids and gases as their temperatures rise

2.2.2.1 Know that a rise in the temperature of an object increases its internal energy

2.2.2.1 Appreciate how a physical property that varies with temperature may be used for the measurement of temperature, and state examples of such properties

2.2.2.2 Describe an increase in temperature of an object in terms of an increase in the average kinetic energies of all of the particles in the object

2.2.2.2 Recognise the need for and identify fixed points

2.2.2.3 Define specific heat capacity as the energy required per unit mass per unit temperature increase; recall and use the equation c = ΔE/mΔθ

2.2.2.3 Describe and explain the structure and action of liquid-in-glass thermometers

2.2.2.4 Describe experiments to measure the specific heat capacity of a solid and a liquid

2.2.2.4 Demonstrate understanding of sensitivity, range and linearity

2.2.2.5 Describe the structure of a thermocouple and show understanding of its use as a thermometer for measuring high temperatures and those that vary rapidly

2.2.2.6 Describe and explain how the structure of a liquid-in-glass thermometer relates to its sensitivity, range and linearity

2.2.3.1 Describe melting and boiling in terms of energy input without a change in temperature

2.2.3.2 (old) Show an understanding of what is meant by the thermal capacity of a body

2.2.3.2 Know the melting and boiling temperatures for water at standard atmospheric pressure

2.2.3.3 Describe condensation and solidification in terms of particles

2.2.3.4 Describe evaporation in terms of the escape of more energetic particles from the surface of a liquid

2.2.3.5 (old) Define specific heat capacity

2.2.3.5 Know that evaporation causes cooling of a liquid

2.2.3.6 Describe the differences between boiling and evaporation

2.2.3.7 (old)Recall and use the equation change in energy=mc∆T

2.2.3.7 Describe how temperature, surface area and air movement over a surface affect evaporation

2.2.3.8 Explain the cooling of an object in contact with an evaporating liquid

2.2.4.5 (old) Use the terms latent heat of vaporisation and latent heat of fusion and give a molecular interpretation of latent heat

2.2.4.6 (old) Define specific latent heat

2.2.4.7 (old)Describe an experiment to measure specific latent heats for steam and for ice

Answer:

Knowledge points:

Solution:

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