Chapter 9 (9.9 - 9.12) - Generators, Transformers, Power across d country

Question 1

What are alternators

Answer 1

Generators that give out Alternating Current (AC)

Question 2

Components of an AC generator

Answer 2

2 slip rings
2 brushes
Rectangular coil
magnet

Question 3

How does an AC generator work

Answer 3

The coil rotates. This cuts the magnetic fields so an emf is generated (faraday’s law)

Each side of the coil travels upwards, downwards, upwards, downwards, etc. Therefore the current flows backwards, forwards, etc.

Question 4

When is the current from an ac gen maximum

Answer 4

When coil is horizontal and cutting field lines at fastest rate

Question 5

How to increase EMF (and current) in AC generator

Answer 5

Increasing number of turns in coils
Increasing area of coil
Using stronger magnet
Rotating coil faster

Question 6

What is mutual induction

Answer 6

When coils are magnetically linked so that the changing of current in one causes an induced emf in the other

Question 7

How to increase the increased mutual induction

Answer 7

Core of the electromagnet goes right throuhg the second coil

Number of turns in the coil on the second coil is increasd

Question 8

When is the emf induced in mutual induction

Answer 8

WHen the electromagnet’s current is switched on or off. This is equivalent to pushing a magnet in or pulling it out respectively. Induces a current for a fraction of a second

Question 9

What does a transformer do
2 types

Answer 9

Increases or decreases AC current

Step up and Step down transformers

Question 10

How does a transformer work

Answer 10

AC flows into the primary coil which is wrapped around an iron core. This leads to an alternating magnetic field being generated. The changing field induces an alternating voltage in the secondary coil

Question 11

Formula for transformer

Answer 11

Output voltage/input voltage = turns on output coil/turns on input coil

Question 12

What is a step up transformer

Answer 12

The secondary coil has more turns than the primary coil

Increases the voltage
Reduces the current (ohm’s law)

Question 13

What is a step down transformer

Answer 13

The secondary coil has less turns than the primary coil

Reduces the voltage
Increases the current (ohm’s law)

Question 14

Power formula in a transformer

Answer 14

Input voltage * Input current = output voltage * output current

Question 15

What happens to power in a transformer

Answer 15

Remains constant since as the voltage increases, the current decreases in prop

vice versa

Question 16

3 stages of power in a country

Answer 16

Generation
Transmission
Distribution

Question 17

Explain entire process of power in a country

Answer 17

Power station
Step-up transformer
High voltage power lines
transformer substation
Power lines
transformer substation
Heavy industry
transformer substation
Light industry
transformer substation
Homes, Schools, Offices, farms, etc.

Question 18

What is the grid

Answer 18

A nationwide supply network for power

Question 19

Adv of the grid

Answer 19

Power stations can be sited away from heavily populated locations

No matter where the power station is located – a power station in an area where the demand is low can be used to supply areas where the demand is high.

Question 20

How is power in a grid distributed

Answer 20

using a series of substations

Question 21

What is a substation

Answer 21

Contain step-down transformers, which reduce the voltage in stages to the level needed by consumers. ​

Question 22

What is the voltage for homes

Answer 22

This voltage is usually between 110 V and 230 V for home consumers, depending on the country.

Question 23

Why is AC used compared to DC

Answer 23

Transformers can be used with AC which make it easier to distribute

Transformers don’t work with DC

Question 24

Formula for power loss

Answer 24

power loss = current * voltage drop
voltage = current * resistance

hence power loss = current^2 * resistance

Question 25

Why is a high voltage used

Answer 25

current is reduced and the heating effect is also reduced. This leads to less power loss because resistance is lesser.

Thinner, lighter and cheaper cables can be used as transmission cables. This saves a lot of money as well as energy. ​

Question 26

Adv and disadv of overhead cables

Answer 26

Adv:
Cheaper
Easier to insulate (air is the insulator)
Money is saved since digging operation costs are avoided

Disadv:
Spoil the environment and its beauty (therefore underground cables are used then)

Question 27

how is emf generated in transformers

Answer 27

alternating current causes magnetic field in iron core
magnetic field changes
field lines get cut
emf is hence induced

Question 28

why do transformers not work with a dc voltage supply?

Answer 28

changing magnetic flux, induces emf in the secondary, no change of flux with a constant dc supply

Question 29

in generators which hand is used

Answer 29

right hand
we can think of it as generator has 2 Rs so right hand