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→Finding Time from Current and Charge
{| class="wikitable"
| style="height:20px; width: 300px; text-align:center;" |A battery charger uses a current of 150mA to deliver a charge of 245 Coloumbs to a battery. Calculate the time taken to charge this battery correct to two [[Significant Figures|significant figures]].
| style="height:20px; width: 300px; text-align:center;" |A cloud in a thunderstorm loses 15kC 15C in one lightening strike. At a current of 31,000kA. Calculate how long this lightning strike lasts correct to two [[Significant Figures|significant figures]].
|-
| style="height:20px; width: 300px; text-align:left;" |'''1. State the known quantities in correct [[unit]]s.'''
I = 31,000kA = 3.1x10<sup>7</sup>A
Q = 15kC = 15x10<sup>3</sup>15C
|-
| style="height:20px; width: 300px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers and [[Evaluate (Maths)|evaluate]].'''
<math>I=\frac{Q}{t}</math>
<math>3.1 \times 10^7 = \frac{15 \times 10^3}{t}</math>
|-
| style="height:20px; width: 300px; text-align:left;" |'''3. [[Rearrange (Maths)|Rearrange]] the equation and [[Solve (Maths)|solve]].'''
| style="height:20px; width: 300px; text-align:left;" |'''3. [[Rearrange (Maths)|Rearrange]] the equation and [[Solve (Maths)|solve]].'''
<math>t=\frac{15 \times 10^3}{3.1 \times 10^7}</math>
<math>t = 4.8387 \times 10^{-47}s</math>
<math>t\approx4.8 \times 10^{-47}s</math>
|}