9702 · 19.1
Capacitors and capacitance flashcards
Revision flashcards for Cambridge 9702 Capacitors and capacitance (syllabus 19.1). Flip, recall, then mark a real past-paper question.
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Define capacitance.
Capacitance is the charge stored per unit potential difference across a capacitor.
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What is the SI unit of capacitance, and how is it defined?
The Farad (F), defined as 1 Coulomb of charge stored per Volt of potential difference (1 C/V).
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Write the formula for the total capacitance of capacitors connected in series.
$$\frac{1}{C_{total}} = \frac{1}{C_1} + \frac{1}{C_2} + \dots$$
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How does the total capacitance of capacitors connected in parallel compare to the individual capacitances?
The total capacitance in parallel is always greater than the largest individual capacitance.
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State two formulas for the energy stored in a capacitor.
$$E = \frac{1}{2}QV$$ or $$E = \frac{1}{2}CV^2$$
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What is a dielectric?
An insulating material placed between the plates of a capacitor to increase its capacitance.
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Draw the standard circuit symbol for a capacitor.
Two parallel lines of equal length, perpendicular to the connecting wires.
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How does total capacitance change when capacitors are connected in series?
The total capacitance decreases and is always less than the smallest individual capacitance.
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What physical feature defines a parallel-plate capacitor?
Two conductive plates placed parallel to each other, separated by a dielectric insulator.
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In a series circuit of capacitors, what quantity is the same across all capacitors?
The charge (Q) stored on each capacitor is the same.
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In a parallel circuit of capacitors, what quantity is the same across all capacitors?
The potential difference (V) across each capacitor is the same.
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How is the energy stored in a capacitor represented on a Q-V graph?
It is represented by the area under the charge-voltage (Q-V) graph.
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What is the formula for the capacitance of a parallel-plate capacitor?
$$C = \frac{\varepsilon A}{d}$$, where ε is the permittivity of the dielectric, A is the overlapping area of the plates, and d is the distance between the plates.
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How does increasing the distance between the plates of a parallel-plate capacitor affect its capacitance?
It decreases the capacitance, as capacitance is inversely proportional to the plate separation (d).
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What physical principle is applied when a charged capacitor is connected to an uncharged one?
The principle of conservation of charge. The total charge before connection is equal to the total charge after connection, which is now distributed across both capacitors.