AQA GCSE HIGHER PHYSICS - Internal Energy and Temperature Changes

AQA GCSE Higher Physics: Internal Energy and Temperature Changes

This tutorial will explore the concepts of internal energy and temperature changes, focusing on how these relate to the kinetic and potential energy of particles within a system.

Internal Energy

• Definition: Internal energy is the total kinetic and potential energy of all the particles within a system.
• Kinetic Energy: This is the energy associated with the motion of particles. The faster the particles move, the higher their kinetic energy.
• Potential Energy: This is the energy associated with the forces between the particles. Think of it as the energy stored within the bonds between particles.

Temperature and Internal Energy

• Temperature: A measure of the average kinetic energy of the particles in a system. A higher temperature indicates faster-moving particles and therefore higher average kinetic energy.
• Relationship: While internal energy includes both kinetic and potential energy, temperature only reflects the average kinetic energy.
  • Important Note: A change in temperature always results in a change in internal energy, but a change in internal energy doesn't always mean a change in temperature. For example, a change in the potential energy of particles (like those in a phase change) can affect internal energy without changing the temperature.

Changes in Internal Energy

Internal energy can change due to:

• Heating: Adding heat energy to a system increases the internal energy. This can cause an increase in the kinetic energy of the particles (raising the temperature), or it can lead to a change in potential energy (like a phase change).
• Doing Work: Work done on a system can also increase its internal energy. This can happen when a system is compressed (increasing the potential energy of particles) or when friction causes energy transfer.
• Cooling: Removing heat energy from a system decreases its internal energy. This can lead to a decrease in kinetic energy (lowering the temperature) or a change in potential energy (like condensation).
• Expansion: A system doing work on its surroundings can decrease its internal energy. For example, expanding gas does work and loses internal energy.

Specific Heat Capacity

• Definition: The specific heat capacity of a substance is the amount of energy needed to raise the temperature of 1 kg of the substance by 1°C.
• Formula: Q = mc?T where:
• Q = energy transferred (in Joules, J)
• m = mass (in kilograms, kg)
• c = specific heat capacity (in Joules per kilogram per degree Celsius, J/kg°C)
• ?T = change in temperature (in degrees Celsius, °C)

Example: Calculating Internal Energy Change

Suppose you heat 500 g of water from 20°C to 80°C. The specific heat capacity of water is 4200 J/kg°C.

1. Convert mass to kilograms: 500 g = 0.5 kg
2. Calculate the temperature change: ?T = 80°C - 20°C = 60°C
3. Calculate the energy transferred: Q = (0.5 kg)(4200 J/kg°C)(60°C) = 126,000 J

Therefore, 126,000 J of energy is needed to raise the temperature of 500 g of water from 20°C to 80°C.

Key Points to Remember:

• Internal energy is the total energy of particles in a system.
• Temperature is a measure of the average kinetic energy of particles.
• Changes in internal energy can occur through heating, cooling, work done on/by the system.
• Specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1°C.

This tutorial provides a basic introduction to internal energy and temperature changes. Further exploration of these concepts can lead to a deeper understanding of heat transfer, thermodynamics, and other related topics.