Schematic Rise

Power and energy are two terms that are often misused. Energy can bethought of as the ability to do work, and it has units such as joules or Btu. Power, on the other hand, is the rate at which energy is generated or used, and therefore it has rate units such as joules/sor Btu/h. There is often confusion about the units for electrical power and energy. Electrical power is measured in watts, which isarate(1J/s=1 watt), so electrical energy is watts multiplied by time—for example, watt-hours.

Be careful not to say”watts per hour,”which is incorrect (eventhoughyou will see this all too often in newspapers or magazines). When a battery delivers current to a load, power is generated by the battery and is dissipated by the load. We can combine (1.1) and (1.2) to find an expression for instantaneous power supplied, or consumed, by a component of a circuit. The key electrical quantities already introduced and the relevant relationships between these quantities are summarized in Table 1.1. Since electrical quantities vary over suchalargerange of magnitudes, you will often find yourself working with very small quantities or very large quantities.

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