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College Physics (Urone)
Found in: Page 696

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Short Answer

Consider a battery used to supply energy to a cellular phone. Construct a problem in which you determine the energy that must be supplied by the battery, and then calculate the amount of charge it must be able to move in order to supply this energy. Among the things to be considered are the energy needs and battery voltage. You may need to look ahead to interpret manufacturer's battery ratings in ampere-hours as energy in joules.

The supplied charge is 13500 C.

See the step by step solution

Step by Step Solution

Step 1: Principle and Formulas

The power supplied by a source to a circuit element :


where Vis the potential difference and is I the current across the element.

The power of a process is

P=ΔEΔt .........................................(2)

where Eis the change in energy and t is change in time.

Step 2: calculating battery supplied energy.

The Charger’s voltage output is: ΔV=5.0 V

The rate of the battery is 3750 mA which means that it can produce a current of 3750 mA for 1 h.

The power supplied by the battery is found from Equation (1):


Substitute for P from Equation (2):


Solve for E:


Step 3: Calculation of the amount of charge supply

The energy supplied by the battery:

Substitute, 3750 mA for / 1 h for \({\rm{\Delta t}}\), and 5.0 for V:

ΔE=(3750 mA)(1 A1000 mA)(5.0 V)(1 h)(3600 s1 h)=67500 J

Converting the ampere-hour rating into coulombs, the amount of charge it must be able to move in order to supply this energy is

q=(3750 mA)(1 A1000 A)(1 h)(3600 s1 h)=13500 C

Therefore, the amount of charge to be supplied is 13500 C.

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