An LED lamp powered by a USB-based portable battery has an effective resistance of 500 Ohm. If the battery is rated for 10,000 mAh, then how long can the lamp be powered and what is the total power consumed by the lamp? The operating voltage of a USB powered device is 5V. Assume that the battery is also rated at 5V.

Time = 1000 h

Power = 0.05 W = 50 mW

Explanation:

First we will find the current consumed by the lamp. For this purpose we can use the Ohm's Law. The equation of Ohm's Law is written as follows:

V = IR

I = V/R

where,

I = Current = ?

V = Voltage = 5 V

R = Resistance = 500 Ω

Therefore,

I = 5 V/500 Ω

I = 0.01 A = 10 mA

Now the time duration of the operation f lamp can be found by:

Time = Rating/Current

Time = 10000 mAh/ 10 mA

Time = 1000 h

The power consumption of lamp is given as follows:

Power = IV

Power = (0.01 A)(5 V)

Power = 0.05 W = 50 mW

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