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

When considering the energy supply for an automobile, energy per unit mass of the energy source is an important parameter. Using the following data, compare the energy per unit mass $(J / k g)$ 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: $126000 \mathrm{Btu} / \mathrm{gal} ;$ 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 refers to the amount of energy stored per unit mass of a fuel or energy storage medium. This is a key metric when evaluating energy sources, as it determines how much energy can be carried or stored relative to the weight of the material. It is particularly important in automotive applications where weight is critical to performance and efficiency.

Unit Conversion

Unit conversion is the process of converting a quantity expressed in one set of units to another set of units. In energy comparisons, this often involves converting non-SI units, such as BTUs, into joules so that different energy sources can be compared directly on a common energy scale.

Electrical Energy Storage in Batteries

Batteries store energy in chemical form and deliver it as electrical energy. The energy stored in a battery can be quantified by using its voltage and capacity (often given in ampere-hours), and this energy must be considered relative to the battery’s mass when evaluating its suitability for applications like automotive energy supply.

Capacitor Energy Storage

Capacitors store energy in an electric field and their energy content can be determined by the formula E = ½CV², where C is the capacitance and V is the voltage across the capacitor. Like batteries, when considering capacitors for energy supply applications, it is important to assess the energy stored per unit mass to evaluate their practicality compared to other energy storage methods.

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