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Static electricity
2. Mica capacitor
the battery, a dielectric material
is carefully inserted between the Note that any arrangement of two
plates. How would the capacitance conductors separated from one
be affected? Justify your answer. another by an insulator forms a
3. A capacitor of capacitance 3 μF capacitor. In an ordinary laboratory,
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stores a total charge of 3.6×10 C. this could be two sheets of metal foil
−5
Calculate the potential difference isolated by small pieces of plastic in
(voltage) across the capacitor. between, with air as the insulating
4. If a cell with a voltage of 1.5 V is material. In a mica capacitor, the
sheets of metal foil are separated by
used to charge a capacitor, calculate strips of mica, as shown in Figure
the capacitor’s capacitance when the 1.29. Mica is preferred because it is a
charge is 90 C. natural mineral and splits easily into
very thin sheets.
Types of capacitors Mica
Different types of capacitors depend on (Dielectric)
the dielectric materials used to make
them. These include the following:
1. Paper or plastic capacitors
A paper or plastic capacitor has metal Metal plates
foil strips as its conductor plates. Figure 1.29: Mica capacitor
Waxed paper or plastic forms the
insulating material. Polyester film 3. Electrolytic capacitor
can also be used as a separating or Metal sheets are separated by paper
insulating material. See Figure 1.28.
Insulating materials are rolled up and previously soaked in a chemical
sealed inside a metal box to prevent compound (Figure 1.30). The soaked
moisture from entering, which could paper is not an insulating material.
reduce the insulation. As the capacitor charges, a thin layer
of aluminium oxide is formed on
Metal foil the positive plate, thereby providing
a thin insulating layer between the
plates. The thinner the layer, the
higher the capacitance. Electrolytic
capacitors are connected with great
care. Their ends are labelled positive
or negative as a safety precaution
Paper because a wrong connection can lead
to an explosion.
Figure 1.28: Paper capacitor
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Physics Form 2 Final.indd 23 25/10/2025 10:25
