Active and Reactive Power in Circuit Elements

Question 1

What are AC circuits

Answer 1

These are circuits that their current/voltage varies with time

Question 2

What are DC circuits

Answer 2

These are circuits that their current/voltage remains constant with time

Question 3

What is Instantaneous Power

Answer 3

This is power that is flowing in a circuit at any instant of time.

Question 4

What is positive power

Answer 4

This is power that flows from the source to the load

Question 5

What is negative power

Answer 5

This is power that flows from the load to the source

Question 6

Why is power always positive in a purely resistive circuit

Answer 6

The voltage and current are always in phase with each other.

Question 7

What is active power

Answer 7

This is the power that is used for doing useful work (It is dissipated in the form of heat or work). Active power is always positive.

Question 8

What are the 4 major properties of active power

Answer 8

It is always positive, It does not change direction, it always flows from source to load, it is denoted by P and measured in Watts.

Question 9

What is Reactive Power

Answer 9

This is the power that is not used for doing useful work (It is not usually dissipated from the circuit). Active power varies between positive and negative.

Question 10

What are the 4 major properties of Reactive power

Answer 10

It is positive as well as negative, It is not used for useful work, It represents power that is going back and forth, It is denoted by Q and measured in VAr (Volt Ampere Reactive)

Question 11

Why does power vary between positive and negative in an inductive and capacitive circuit (Non Linear Circuit Elements)

Answer 11

Because the voltage and current are out of phase by 90 degrees.

Question 12

What is Apparent power

Answer 12

This is a combination of both active and reactive power. S = P2 + Q2

Question 13

What is Power factor

Answer 13

Power factor is the ratio of active power to apparent power in a circuit.

Question 14

What do we mean when we say a circuit element ‘consumes’ a certain type of power

Answer 14

The circuit element draws or absorbs a certain type of power.

Question 15

What do we mean when we say non-linear circuits consume reactive power

Answer 15

They cycle power back and forth between the source

Question 16

What happens when current flows through a conductor?

Answer 16

A magnetic field forms around the conductor

Question 17

What is the process of generating a magnetic field?

Answer 17

Electromagnetism

Question 18

What is the basic principle of a Resistor

Answer 18

A resistor opposes the flow of electrons

Question 19

What is the basic principle of an inductor

Answer 19

An inductor opposes the change in the flow of electrons

Question 20

What device is created to take advantage of electromagnetism

Answer 20

An inductor

Question 21

Why are inductors always in form of a coil

Answer 21

Because it creates more magnetic field

Question 22

When current is maximum in a magnetic field what happens in an inductor

Answer 22

There is great energy storage

Question 23

What does an iron core in a magnetic field do

Answer 23

Strengthens a magnetic field

Question 24

What’s a ferromagnetic material

Answer 24

This is a material that can be magnetised and demagnetized easily.

Question 25

What is inductance?

Answer 25

This is a measure of an inductor's ability to store energy for a given amount of current flow

Question 26

What are the four major factors affecting inductance

Answer 26

Number of turns, Area of coil, Length of coil, core material

Question 27

How does an inductor regulate the flow of current

Answer 27

By varying the voltage. If current is increasing, voltage will push against electron flow. If current is decreasing, voltage will push the electron flow.

Question 28

What's the resultant active power consumed by an inductor

Answer 28

Zero

Question 29

What is the basic working principle of a capacitor

Answer 29

A capacitor opposes the change in voltage. It varies the current in a circuit to keep the voltage constant.

Question 30

What are the RLC parameters of a purely capacitive circuit

Question 31

What are the RLC parameters of a purely inductive circuit

Question 32

Why does current lag voltage in an inductive circuit

Answer 32

When voltage is applied across an inductor, the current cannot instantaneously reach its maximum value because an inductor opposes changes in current. As a result, the voltage reaches its maximum before current does

Question 33

Why does current lead the voltage in a capacitive circuit

Answer 33

When voltage is applied across a capacitor, the capacitor resists the change in voltage and therefore current reaches its peak first before voltage