Question

A 70.0-μμF capacitor has an initial charge of 700.0 μμC.

1)

If a resistance of 60.0 ΩΩ is connected across it, what is the initial current through the resistor? (Express your answer to one significant figure.)

mA = units

answer is not 100 or 200

Answer 1

Voltage accross the capacitor can be given by charge/Capacitance

i.e. V = Q/C

V = 700.0C/70.0F = 10.0 V

Now to find current, we use ohm's law V = i*R

i= V/R

i= 10.0/60.0 = 0.17A = 170mA

But the answer is asked in one significant number.

The problem here is if you write 170 then significant numbers are 2, so to reduce them we round off to, 200.

Now 200 has 1 significant figure, but when written with unit, both the zeroes also become significant, i.e. 200mA has three significant figure.

So we have to convert it to a multiplier,

That is, we should write 2 x 10² mA, since multipliers are insignificant hence this is the final answer.