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10.6 Chapter summary (ESCQ2)

Presentation: 27XW

  1. Ohm's Law governs the relationship between current and potential difference for a circuit element at constant temperature. Mathematically we write \(I=\frac{V}{R}\).

  2. Conductors that obey Ohm's Law are called ohmic conductors; those that do not are called non-ohmic conductors.

  3. Ohm's Law can be applied to a single circuit element or the circuit as a whole (if the components are ohmic).

  4. The equivalent resistance of resistors in series (\({R}_{s}\)) can be calculated as follows: \({R}_{s}={R}_{\text{1}}+{R}_{\text{2}}+{R}_{\text{3}}+...+{R}_{n}\)

  5. The equivalent resistance of resistors in parallel (\({R}_{p}\)) can be calculated as follows: \(\frac{\text{1}}{{R}_{p}}=\frac{\text{1}}{{R}_{\text{1}}}+\frac{\text{1}}{{R}_{\text{2}}}+\frac{\text{1}}{{R}_{\text{3}}}+...+\frac{\text{1}}{{R}_{n}}\)

  6. Real batteries have an internal resistance.

  7. The potential difference \(V\) of the battery is related to its emf \(\mathcal{E}\) and internal resistance \(r\) by:

    \begin{align*} \mathcal{E}& = V_{\text{load}} + V_{\text{internal resistance}}\\ &\text{or} \\ \mathcal{E}& = IR_{Ext} + Ir \end{align*}
  8. The external resistance in the circuit is referred to as the load.

Physical Quantities
QuantityUnit nameUnit symbol
Current (\(I\))Amperes\(\text{A}\)
Electrical energy (\(E\))Joules\(\text{J}\)
Power (\(P\))Watts\(\text{W}\)
Resistance (\(R\))Ohms\(\text{Ω}\)
Voltage / Potential difference (\(V\))Volts\(\text{V}\)

Table 10.1: Units used in electric circuits