Capacitor

CHAPTER 1
Capacitor & Dielectric

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1.1 1.2 1.3 1.4 1.5

Capacitance Capacitor in series & parallel Energy stored in a charged capacitor Charging & discharging of capacitors Capacitors with dielectric

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1.1 Capacitance
Learning Outcomes :
At the end of this topic, students should be able to:  Define capacitance  Use the capacitance formula  Determine capacitance of parallel plate

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 A capacitor is electric component to store electric charge  It consists two parallel conductors plates, one positively charged and the other is negatively charged  The two plates are placed parallel with each other at a small distance apart

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Symbol

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 The conducting plates could be in the shape of : i. cylindrical ii. spherical iii. parallel plate

cylindrical

spherical

Parallel plate

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Charging & Discharging
 When a capacitor is connected to a circuit with Direct Current (DC) source, two processes, which are called “charging” and “discharging” the capacitor will happen i. Charging process

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The capacitor is connected to the DC power supply and current flows through the circuit

Charging process

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

Both plates get the equal and opposite charges and an increasing potential difference, vc, is created while the capacitor is charging Once the voltage at the terminals of the capacitor, vc, is equal to the power supply voltage, vc = V, the capacitor is fully charged and the current stops flowing through the circuit

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ii.

Discharging process

 When the capacitor disconnected from the power supply, the capacitor is discharging through the Resistor RD and the voltage between the plates drops down gradually to zero, vc = 0

Discharging process

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 Figure