Internal Resistance notes

they call this advanced communication techniques (collusion)(this is a joke, to my knowledge this is not collusion)

Investigation: 30 marks

1. Define Internal Resistance (2) The resistance within a battery or cell caused by the movement of current through internal materials of the source which have resistance. Literally copy paste the definition from the handout
2. Draw circuit of experiment (3)
3. Does EMF/Internal Resistance change from new to old batteries? (3)

• Yes, as batteries get older internal resistance increases.
• As the battery gets older, the conductive material of the battery starts to wear, usually via corrosion, and the electrolyte decreases in concentration,
• so the rate at which electrons can be transferred through the battery decreases, hence internal resistance increases.

1. 2 factors affecting Internal Resistance (4)

• Temperature, affecting reaction rate and thus the rate at which the chemical process for the discharge of electrons, which affects internal resistance.
• Electrolyte concentration, which affects how charge passes through the electrolyte to complete the internal circuit, affecting the internal resistance.

2. Graph of new, old cell (5)
3. Identify which was old, and explain (2)(3)

• {{line}} was the oldest battery, as it has the most negative gradient and the lower y-intercept on the graph.

• Which correlates to a higher internal resistance and a lower $EMF$, and thus an older battery

• Hence, rearranging, each line can be described by the equation $V=-R_{\text{Internal}}I+\epsilon$.

• Hence, as {{line}} has the more negative gradient, it will have the greater internal resistance as $\text{Grad} = -R_{\text{Internal}}$.

• So {{line}} will be the oldest as internal resistance increases over time.

• has the most negative gradient, and thus the highest internal resistance, and

7. Calculate Internal Resistance, by gradient (3)(2)

$$\begin{align} V&=IR \text{ (Ohm's law)}& \\ \therefore \epsilon&=IR_{T}& \\ \text{But } R_{T} &= \text{ external resistance + internal resistance}&\\ \therefore \epsilon&=I(R+R_{I}) \\ \epsilon&=V+R_{I}I \\ \therefore V&=-R_{I}I+\epsilon& \\ \text{So } -&R_{I}=\text{Gradient}\\ \end{align} $$

8. Uncertainty. Absolute and %. (3) just game

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