ITPEC IP October 2023 Question 16
In the specification of the capacity of a battery that is embedded in a device such as an IoT device or a smartphone, which of the following is the appropriate meaning of “100mAh”?
Explanation
It can discharge a current of 100mA for one hour — mAh (milliampere-hour) is current multiplied by time.
The capacity is the current the battery can supply times how long it can supply it: 100 × 1 = 100 mAh for 100 mA over one hour. Ideally the same battery gives 50 mA for two hours or 200 mA for half an hour. A device that draws 20 mA runs about 100 ÷ 20 = 5 hours. The unit says nothing about charging, which depends on the charger's current.
Answer (a)
Why not others:
- •(b) and (d) — read the rating as a charging time; mAh measures the charge stored, not how long it takes to charge
- •(c) — 1 A is 1,000 mA and 100 minutes is about 1.67 hours, so 1000 × 1.67 ≈ 1667 mAh, about 17 times the rating; it takes the 100 as minutes and the milli away
Key rule: Dividing a battery's capacity in mAh by the device's current in mA gives its running time in hours.
Hardware · AI-written, may contain errors
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