Question

Your cell phone typically consumes about 390 mW of power when you text a friend. If the phone is operated using a lithium-ion battery with a voltage of 3.5 V, what is the current flowing through the cell-phone circuitry under these circumstances?

Answer 1

Answer:

I = 0.11 A

Explanation:

• In an electric circuit, the power delivered to a load, is just the product of the potential difference between the load terminals, times the current flowing through it, as follows:

       $P = V*I$

• In this case, the power is the one consumed by the cell phone = 390 mW, and the voltage the one produced by the internal energy of the battery, 3.5 V, neglecting the voltage loss at the internal resistance of the battery.
• So, we can solve the above equation for  the current I, as follows:

        $I = \frac{P}{V} = \frac{0.39W}{3.5V} = 0.11 A$

• The current flowing through the cell-phone circuitry is 0.11 A.