Energy
In electrical circuits, attention is often devoted to power, but sometimes we would also like to know the total energy transferred for a given period of time. For example, energy usage determines how long the battery in your circuit will last or what your electricity bill will be. Recalling that power is the rate of work, energy (w) is defined as
The SI unit of energy is the joule (J). Noting that energy is the product
of power and time (1 joule = 1 watt × 1 second), it is also convenient to
define energy in terms of watt-hours (Wh) or kilowatt-hours (kWh). Electric utilities typically charge for electricity usage in units of kWh, and this
unit is typically displayed on the dashboard or display of electric vehicles.
Converting units yields the relations
1 Wh = 3600 J........... [6]
1 kWh = 3.6 × 106 J .............[7]
Battery capacity (energy stored) can also be defined in terms of Wh.
Since the voltage on a battery is constant, it becomes convenient to separate out the battery voltage and simply refer to the total charge storage
on the battery (Q). Thus,
The total charge Q is given in units of amp hours (Ah) or milliamp hours
(mAh)
Question- A battery-powered smoke detector has an average power consumption of 0.5 mW and runs on a 9 V battery with a capacity of
500 mAh. How often do you expect to change the battery?
write your answer in comment
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