Energy transfers IB DP Physics Study Notes - 2025 Syllabus
Energy transfers IB DP Physics Study Notes
Energy transfers IB DP Physics Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Physics syllabus with Students should understand
- Energy transfers
- energy density of the fuel sources
Standard level and higher level: 9 hours
Additional higher level: There is no additional higher level content
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
Energy Transfers
An energy transfer occurs when energy moves from one object or system to another. This can happen in the same form (e.g., kinetic to kinetic) or involve conversion between different forms (e.g., electrical to thermal).
Energy is transferred through mechanisms such as:
- Mechanical work (force × displacement)
- Heating (thermal conduction, convection, or radiation)
- Electrical work (current × voltage × time)
- Wave motion (sound, light)
The total energy is conserved, but the form and location of energy may change. The concept of energy transfer is essential for understanding how systems operate and where losses occur (e.g., heat loss in machines)
In many real systems, part of the energy is transferred to surroundings and becomes less useful, typically as thermal energy due to friction or resistance.
Example:
An electric kettle takes in 2000 J of electrical energy and heats water. Out of this, 1600 J goes into heating the water. Calculate the energy wasted and identify the transfer processes involved.
▶️ Answer/Explanation
Step 1: Calculate energy wasted
Energy wasted = \( 2000 – 1600 = \boxed{400 \, \text{J}} \)
Step 2: Describe energy transfers
Electrical energy is transferred to thermal energy in the heating coil.
Useful energy: thermal energy transferred to water.
Wasted energy: thermal energy lost to surroundings and kettle body (by conduction and radiation).
Conclusion:
This is an example of energy transfer with partial energy loss, common in most devices.
Energy Density of Fuel Sources
The energy density of a fuel is defined as the amount of energy released per unit mass (or sometimes per unit volume) of the fuel when it is completely combusted or used.
It is a key parameter when comparing fuels for efficiency, transportability, and storage.
There are two common types:
- Specific energy — energy per unit mass (J/kg)
- Energy density — energy per unit volume (J/m³)
\( \text{Specific Energy} = \frac{\text{Energy Released}}{\text{Mass of Fuel}} \quad \text{(units: J/kg)} \)
\( \text{Energy Density} = \frac{\text{Energy Released}}{\text{Volume of Fuel}} \quad \text{(units: J/m}^3\text{)} \)
Fuels with high energy densities (like gasoline or nuclear fuel) are preferred for applications where space or mass is limited (e.g. transport, aerospace).
Specific Energy and Energy Density of Common Fuel Sources
| Fuel Source | Specific Energy (J/kg) | Energy Density (J/m³) |
|---|---|---|
| Gasoline (Petrol) | \( 4.6 \times 10^7 \) | \( 3.4 \times 10^{10} \) |
| Diesel | \( 4.5 \times 10^7 \) | \( 3.6 \times 10^{10} \) |
| Natural Gas (Methane) | \( 5.5 \times 10^7 \) | \( 3.9 \times 10^7 \) |
| Coal | \( 3.0 \times 10^7 \) | \( 2.4 \times 10^{10} \) |
| Ethanol | \( 3.0 \times 10^7 \) | \( 2.4 \times 10^{10} \) |
| Hydrogen (compressed gas) | \( 1.2 \times 10^8 \) | \( 8.4 \times 10^6 \) |
| Uranium-235 (nuclear) | \( 8.0 \times 10^{13} \) | Very High (solid fuel) |
Note: Fossil fuels tend to have higher energy densities than renewables like biomass, but also contribute to CO₂ emissions and pollution.
Example:
Petrol (gasoline) has a specific energy of approximately \( 4.6 \times 10^7 \, \text{J/kg} \), and a density of \( 740 \, \text{kg/m}^3 \). Find the energy density of petrol in J/m³.
▶️ Answer/Explanation
Step 1: Use formula for energy density
\( \text{Energy Density} = \text{Specific Energy} \times \text{Density} \)
Step 2: Substitute values
\( = (4.6 \times 10^7) \times (740) = \boxed{3.404 \times 10^{10} \, \text{J/m}^3} \)
Interpretation:
Petrol releases over \( 3 \times 10^{10} \, \text{J} \) of energy per cubic meter, explaining why it’s widely used as a high-performance fuel.