When considering the energy supply for an automobile, the...

When considering the energy supply for an automobile, the energy per unit mass of the energy source is an important parameter. Using the following data, compare the energy per unit mass ( $J /$ kg) for gasoline, lead-acid batteries, and capacitors. (The ampere A will be introduced in the next chapter as the SI unit of electric current. $1 \mathrm{A}=1 \mathrm{C} / \mathrm{s} .)$ Gasoline: 126000 Btu/gal; density $=670 \mathrm{kg} / \mathrm{m}^{3}$ Lead-acid battery: $12.0 \mathrm{V} ; 100 \mathrm{A} \cdot \mathrm{h} ;$ mass $=16.0 \mathrm{kg}$ Capacitor: potential difference at full charge $=12.0 \mathrm{V}$ capacitance $=0.100 \mathrm{F} ;$ mass $=0.100 \mathrm{kg}$.

When considering the energy supply for an automobile, the energy per unit mass of the energy source is an important parameter. Using the following data, compare the energy per unit mass ( $J /$ kg) for gasoline, lead-acid batteries, and capacitors. (The ampere A will be introduced in the next chapter as the SI unit of electric current. $1 \mathrm{A}=1 \mathrm{C} / \mathrm{s} .)$
Gasoline: 126000 Btu/gal; density $=670 \mathrm{kg} / \mathrm{m}^{3}$ Lead-acid battery: $12.0 \mathrm{V} ; 100 \mathrm{A} \cdot \mathrm{h} ;$ mass $=16.0 \mathrm{kg}$
Capacitor: potential difference at full charge $=12.0 \mathrm{V}$ capacitance $=0.100 \mathrm{F} ;$ mass $=0.100 \mathrm{kg}$.

Key Concepts

Energy Density

Energy density, often expressed in joules per kilogram (J/kg), is the amount of energy stored in a given mass of a fuel or storage medium. It is a crucial parameter in evaluating various energy sources for applications such as automotive propulsion since a higher energy density means more energy can be stored in a lighter system, which is particularly important for vehicles.

Unit Conversion

Unit conversion involves translating measurements from one unit system to another to ensure consistent analysis, particularly converting non?SI units like British Thermal Units (Btu) into the SI unit joules (J) when calculating energy. This process is essential for comparing the energy content of different materials and technologies on a common basis.

Electrochemical Energy Storage

Electrochemical energy storage refers to the method by which batteries store energy. Batteries convert chemical energy into electrical energy, and their energy content is often given in terms of ampere-hours (Ah) multiplied by the battery voltage. Converting this measure to joules allows for a direct comparison with other energy storage systems like fuels and capacitors.

Capacitive Energy Storage

Capacitive energy storage is based on storing electrical energy in an electric field created between two conductors. The energy stored in a capacitor is calculated using the formula E = 1/2 CV², where C is the capacitance and V is the voltage. This method of energy storage is fundamentally different from chemical storage and typically results in much lower energy density compared to fuels or batteries.

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