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→Example Calculations
<math>Q = 2100C</math>
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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 240 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 in one lightening strike. At a current of 30,000kA. Calculate how long this lightning strike lasts correct to two [[Significant Figures|significant figures]].
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| style="height:20px; width: 300px; text-align:left;" |'''1. State the known quantities'''
I = 150mA = 150x10<sup>-3</sup>A
Q = 240C
| style="height:20px; width: 300px; text-align:left;" |'''1. State the known quantities'''
I = 30,000kA = 3x10<sup>7</sup>A
Q = 15kC = 15x10<sup>3</sup>
|-
| 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>150 \times 10^{-3} = \frac{240}{t}</math>
| 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 \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]].'''
<math>t=\frac{240}{150 \times 10^{-3}}</math>
<math>t=1600s</math>
| 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 \times 10^7}</math>
<math>t = 5.0 \times 10^{-4}s</math>
|}