Electronics Theories

Question 1

What is pulsating DC ?

Answer 1

• Pulsating DC (PDC) is a type of direct current (DC) that varies in magnitude but never changes direction
• DC fluctuates between zero and a peak value.

Question 2

Adding any number of sine waves of the same frequency will always produce a sine wave of the same frequency with unique magnitude and phase.

TRUE OR FALSE

Answer 2

TRUE

Question 3

Which waveform is leading/lagging ?

Answer 3

Question 4

What is RMS voltage ?

Answer 4

• Equivalent dc voltage that would deliver the same power to a load as ac voltage
• Same formula for current rms

Question 5

What are the formulas for ac ohm’s law and power law. (For 100% ohmic element)

Answer 5

Question 6

What happens when a charged capacitor is grounded at only one side ?

Answer 6

• no discharge occurs, direct path must exist btw the 2 plates.

Question 7

What is capacitance ?

Answer 7

• The ratio of the electric charge on one plate to the potential difference (voltage) between the plates.

Question 8

What is leakage current in capacitors?

Answer 8

• Is the small amount of unintended current that flows across the dielectric material when a capacitor is charged.

Question 9

How do electrolytic capacitors work ?

Answer 9

• They use aluminium-foil plates with semi conducting chemical compound btw them.
• Dielectric = thin film of insulating material, forms on 1 set of plate through electrochemical action when dc volt is applied
• NOT used in ac applications

Question 10

What happens to voltage and current during capacitor charging and discharging?

Answer 10

Question 11

What is energy formula for capacitor ?

Answer 11

Question 12

What is RC Time Constant ?

Answer 12

• RC time constant is the time it takes for the voltage across the capacitor to either charge or discharge to approximately 63.2% or 37.8% of its final value.
• Capacitor fully charges or discharges after 5 time constant ( 5 tau)

Question 13

what is stray capacitance ?

Answer 13

• its unintentional capacitance that exists between parts of a circuit that are not supposed to act as capacitors.
• This happens due to the close proximity of conductors, like wires or circuit traces, which can cause a bit of a charge buildup between them.

Question 14

What are the formulas for capacitors in parallel and in series ?

Answer 14

• Capacitors in parallel add up.
• Voltage limited to the capacitor with smallest volt rating
• For cap in series, total cap < smallest cap

Question 15

What does the graph of AC current applied to capacitor look like.

Answer 15

Question 16

Is power dissipated in capacitive reactance as heat or any form of energy ?

Answer 16

• Capacitive reactance doesn’t dissipate power, energy is alternately stored and released with each AC cycle

Question 17

What is Self Resonant Frequency in capacitors ?

Answer 17

• It’s the frequency where the capacitor’s own inductive and capacitive properties cancel each other out.
• Beyond this point, the capacitor’s impedance starts to increase, and it behaves like an inductor.
• Defines the maximum effective frequency range of the capacitor.

Question 18

What is the formula for capacitive divider ?

Answer 18

Question 19

What is the relationship btw electromagnetic fields and stationary, moving(constant velocity) and accelerating charges ?

Answer 19

• Stationary Charge = electric fields surround the charge
• Moving Charge = magnetic field surround moving charge
• Accelerating Charge = kink created in electromagnetic field, electromagnetic waves radiates out.

Question 20

What happens to the magnetic fields of electrons in a conductor without applied voltage?

Answer 20

Without applied voltage, the magnetic fields of electrons point in random directions, resulting in a net magnetic field of zero.

Question 21

What occurs when a voltage is applied across a conductor in context of magnetic field?

Answer 21

When a voltage is applied, free electrons gain a drift component, generating a net magnetic field.

Question 22

What is the direction of the magnetic field in relation to conventional current flow?

Answer 22

The magnetic field is perpendicular to the direction of conventional current flow and follows the right-hand rule.

Question 23

What is the right-hand rule?

Answer 23

In the right-hand rule, your thumb points in the direction of conventional current flow, and your fingers curl in the direction of the magnetic field.

Question 24

What generates the magnetic field in a permanent magnet?

Answer 24

• By the motion of unpaired electrons orbiting the nucleus of an atom.

Question 25

What role does the lattice structure of ferromagnetic materials play?

Answer 25

The lattice structure fixes a large portion of atomic magnetic dipoles in a fixed direction, creating a net magnetic dipole.

Question 26

How does placing a ferromagnetic material inside a solenoid affect the magnetic field?

Answer 26

Placing a ferromagnetic material inside a solenoid increases the magnetic field strength by aligning the core's atomic magnetic dipoles.

Question 27

How do you determine the direction of force on a positive charge in a magnetic field?

Answer 27

- Use your right hand - Left hand for negative charge

Question 28

What happens when a charge moves parallel to the applied magnetic field?

Answer 28

It experiences no force due to the magnetic field.

Question 29

What is the interaction between two wires carrying current?

Answer 29

The net magnetic field of one wire will exert a force on the other wire and vice versa, provided the current is fairly large.

Question 30

According to Faraday's law, what induces EMF in a circuit?

Answer 30

EMF is directly proportional to the time rate of change of the magnetic flux through the circuit.

Question 31

What are the ways EMF can be induced in a circuit?

Answer 31

1. The magnitude of B can vary with time 2. The area of the circuit can change with time 3. The angle between B and the normal of A can change with time 4. Any combination of these can occur.

Question 32

What is the difference between an AC generator and a DC generator?

Answer 32

A DC generator uses a split ring or commutator for contacts, resulting in a pulsating direct current.

Question 33

What is self-inductance?

Answer 33

Self-inductance is the phenomenon where a looped wire generates an induced EMF due to the varying current passing through it.

Question 34

What does Faraday's law of induction state regarding self-induction?

Answer 34

According to Faraday’s law of induction, self-induction occurs when the magnetic field through a loop grows or shrinks due to changes in current.

Question 35

What is the role of self-induction in inductors?

Answer 35

- Used to store and release energy as current levels fluctuate in time-dependent circuits.

Question 36

What happens when a switch in a circuit is closed? (In relation to self-induced EMF)

Answer 36

When the switch is closed, the current does not jump immediately to V/R; instead, it increases rapidly, inducing an EMF that opposes the current flow.

Question 37

What is a self-induced EMF?

Answer 37

A self-induced EMF is the induced EMF that opposes the current flow in a circuit when the current changes.

Question 38

How do inductors differ from simple circuits regarding self-induction?

Answer 38

Inductors are designed to generate large concentrations of magnetic flux and experience significant self-induction during changes in current.

Question 39

What is the common geometry of inductors?

Answer 39

Inductors commonly have a looplike geometry, such as solenoids, toroids, or spiral shapes.

Question 40

What is the advantage of using a magnetic core in inductors?

Answer 40

Using a magnetic core allows for generating higher magnetic field densities and achieving desired inductance with fewer turns of wire.

Question 41

What are adjustable inductors?

Answer 41

Adjustable inductors are inductors whose effective coil length can be altered, typically using a slider or a slug made of different materials.

Question 42

What is a ferrite bead?

Answer 42

A ferrite bead is a device that increases the inductance of a wire by placing it through a hollow bead, absorbing RF radiation and converting it into heat.

Question 43

What is the typical application of ferrite beads?

Answer 43

Ferrite beads are often used on cables to prevent RF radiation (EMI) from interfering with electronic equipment.

Question 44

What is the primary function of an inductor?

Answer 44

An inductor acts like a time-varying current-sensitive resistance, resisting changes in current.

Question 45

How does an inductor behave under steady-state DC conditions?

Answer 45

Under steady-state DC conditions, an inductor passes current as if it were a wire.

Question 46

What happens when voltage increases across an inductor?

Answer 46

The inductor acts like a time-dependent resistor, resisting rapid increases in current.

Question 47

What occurs when voltage decreases across an inductor?

Answer 47

The inductor acts like a time-dependent voltage source, attempting to keep current flowing.

Question 48

What is reverse and forward EMF in the context of an inductor?

Answer 48

- Reverse EMF is the induced EMF that points in the opposite direction of the applied voltage during an increase in current. - Forward EMF is the induced EMF that points in the same direction as the applied voltage during a decrease in current.

Question 49

What happens when an inductor is energized and de-energized suddenly?

Answer 49

- Electrical energy is transformed into a magnetic field, and inductive behavior affects circuit dynamics. - The magnetic field energy is transformed back into electrical energy, affecting current flow.

Question 50

What is the effect of closing a switch in an inductor, capacitor and resistor circuit?

Answer 50

- The lamp will light up brightly but quickly dims out due to the inductor's high initial impedance. - The lamp slowly builds up in brightness until it reaches maximum illumination. - Free-electron flow is essentially instantaneous, and the brightness of the lamp remains constant.