Module 3: Capacitance Basics

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Questions and Answers

Which of the following factors does NOT affect capacitance?

Distance between plates

Area of plates

Surface temperature of the capacitor (correct)

Number of plates

What is the effect of increasing the distance between the plates of a capacitor?

Capacitance increases

Capacitance becomes unstable

Capacitance decreases (correct)

Capacitance remains the same

What describes the behaviour of a capacitor during its charge and discharge cycle?

Capacitors charge and discharge instantaneously

Capacitors charge and discharge exponentially (correct)

Capacitors discharge but do not charge

Capacitors charge but do not discharge

In a series circuit containing capacitors, how does the total capacitance compare to the individual capacitances?

Total capacitance is less than the smallest individual capacitance Signup and view all the answers

What is the significance of the dielectric constant in capacitor function?

It affects the amount of charge the capacitor can store Signup and view all the answers

What is the capacitance value of a capacitor marked as 2.2 µF with a tolerance of +/- 10%?

2420 pF Signup and view all the answers

What is an exponential charge curve in a capacitive circuit?

Voltage across the capacitor rises exponentially. Signup and view all the answers

In variable capacitors, what is the primary means of varying the capacitance?

Varying the plate area. Signup and view all the answers

Which statement is true about trimmer capacitors?

They allow small capacitance adjustments via a screw mechanism. Signup and view all the answers

How does resistance affect charge time in an RC circuit?

Higher resistance increases the time it takes to reach maximum charge. Signup and view all the answers

What tolerance is typically associated with a capacitor rated at 0.1 µF?

+/- 20% Signup and view all the answers

What is the relationship between capacitance and the charge time in an RC circuit?

Increased capacitance leads to a longer charge time. Signup and view all the answers

What letter indicates a tolerance of +/- 2.0 pF for capacitors over 10 pF?

G Signup and view all the answers

What does the time constant represent in an RC circuit?

Time required for voltage across capacitor to reach 63.2% of source voltage Signup and view all the answers

How is the time constant (TC) calculated in an RC circuit?

TC = R x C Signup and view all the answers

In the given circuit with a 10 kΩ resistor and a 100 µF capacitor, what is the time constant?

1 second Signup and view all the answers

What voltage will the capacitor reach after one time constant in the specified RC circuit?

63.2 volts Signup and view all the answers

How long will it take for the capacitor to completely discharge in a circuit with a time constant of 0.4 seconds?

2.0 seconds Signup and view all the answers

What percentage of voltage does a capacitor retain after one time constant during discharge?

36.8% Signup and view all the answers

What is required for current to flow in an RC circuit?

The circuit must be closed Signup and view all the answers

How does the discharge of the capacitor differ from its charging process?

Both processes follow exponential rules Signup and view all the answers

What is the primary function of a capacitor?

To store electrical charge Signup and view all the answers

What occurs when the potential difference across capacitor plates equals the applied voltage?

Current flow ceases Signup and view all the answers

When a fully charged capacitor is reversed in polarity, what happens first?

The plates discharge themselves Signup and view all the answers

What happens to the charge on the capacitor when DC is applied?

Capacitor blocks the current flow Signup and view all the answers

What is the behavior of a capacitor when an AC voltage is applied?

It charges in both directions Signup and view all the answers

Why does the capacitor block DC once fully charged?

The electric field stabilizes Signup and view all the answers

What is the role of the dielectric in a capacitor?

To separate the plates Signup and view all the answers

What is created between the plates of a capacitor when voltage is applied?

An electric field Signup and view all the answers

Which factor does NOT affect the capacitance of a capacitor?

Type of conductor used Signup and view all the answers

What is the effect of increasing the area of the plates in a capacitor?

It increases the capacitance Signup and view all the answers

How does the distance between the plates affect capacitance?

Closer plates increase capacitance Signup and view all the answers

What describes the charge and discharge process of a capacitor?

Exponential charge and discharge with specific time constants Signup and view all the answers

Which capacitor type is known for having the widest range of capacitance values?

Electrolytic capacitors Signup and view all the answers

What indicates a capacitor's ability to hold voltage?

The voltage rating Signup and view all the answers

What is a common method to generate static electricity?

By friction between two materials Signup and view all the answers

What should be observed during the visual inspection of a capacitor?

Swelling or bulging on the sides or top Signup and view all the answers

Which tool is NOT typically used to verify the correct capacitance of a capacitor?

Analog clock Signup and view all the answers

What is the first step to ensure safety when handling capacitors?

Discharge the capacitor completely Signup and view all the answers

How should the test leads be connected when testing a polarised capacitor?

Red to positive terminal Signup and view all the answers

What indicates a good capacitor when using an analogue ohmmeter?

Resistance starts low and gradually increases Signup and view all the answers

What happens if the resistance measured by an ohmmeter starts low and doesn’t increase?

The capacitor is shorted Signup and view all the answers

What calculation is performed to determine the capacitance using a DC power supply and series resistor?

Using the time constant formula $TC = RC$ Signup and view all the answers

What is a critical warning during the capacitor testing process?

Ensure the capacitor is fully discharged prior to handling Signup and view all the answers

Study Notes

Module 3: Electrical Fundamentals - Topic 3.9: Capacitance/Capacitor

Capacitors store electrical charge
A capacitor has two conductive plates separated by an insulator (dielectric)
Applying a voltage causes electrons to move from one plate to the other, creating a charge.
The amount of charge a capacitor can store depends on several factors, including the distance and area of the plates, the number of plates, the dielectric material, and the working voltage.
Capacitance is the ratio of charge to voltage (C = Q/V).
The higher the capacitance, the more charge can be stored.
Capacitance depends on the physical characteristics of the plates (area, distance) and the dielectric constant of the material between them.
Different capacitor types use various dielectric materials (e.g., paper, mica, ceramic, electrolytic, tantalum) to affect their capacitance, working voltages, and overall function.
Factors affecting capacitance include the area of the plates, the distance between the plates, the number of plates, and the dielectric constant of the insulator.
Capacitors can be arranged in series and parallel configurations, affecting the overall capacitance.
In series circuits, the total capacitance is calculated using a formula related to reciprocal of capacitance values.
In parallel circuits, the total capacitance is directly proportional to the sum of all individual capacitance values.
Capacitors have different voltage ratings (max voltage before dielectric breakdown occurs).
Exceeding the capacitor's working voltage can cause dielectric breakdown, leading to failure.
Capacitance is measured in units of farads (F), microfarads (µF), or picofarads (pF)
A capacitor stores energy in the electric field between its plates
Applying voltage to a capacitor creates an exponentially increasing charge and voltage. A capacitor charges exponentially to the applied voltage, approaching a steady-state.
Voltage across a growing capacitor (RC circuit): voltage rises towards source voltage, exponentially.
The rate of charging and discharging of a capacitor is measured by its time constant.
Time constant (TC) depends on resistance (R) and capacitance (C)
TC = R x C (where R is resistance in ohms, C is capacitance in farads, and TC is time constant in seconds).

Testing Capacitors

Initially, visually inspect for bulging.
Check if it is swollen or bulged on the casing.
Ensure that the capacitor is fully discharged before testing or removal.
Using capacitance meters, digital multimeters(DMM) or analog ohmmeters.
Check polarity to make sure red lead is connected to the positive terminal.
If resistance is low and gradually increases, then the capacitor is healthy
If resistance is high and relatively remains the same, the capacitor is open.
If the resistance is low and doesn't increase, then the capacitor is shorted.

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Description

Explore the fundamentals of capacitance and capacitors in this quiz. Understand how capacitors store electrical charge, the effect of plate characteristics, and various dielectric materials. Test your knowledge on how capacitance is calculated and the factors influencing it.