3.4 Generation of Electricity

Question 1

How is static electricity generated?

Answer 1

Via friction between two insulating materials rubbing together.

Question 2

How do you find out which materials become positive and which negative when rubbed together?

Answer 2

Triboelectric chart, Higher on the chart = positively charged (loses electrons), lower on chart = Negatively charged (gains electrons)

Question 3

Aircraft utilise static dischargers and position them where?

Answer 3

To minimise interference with radio systems where friction can pick off the positive or negative charge.

Question 4

How do crystals (quartz) generate voltage?

Answer 4

When ever stresses are applied to their surfaces: pressure, squeezed.

Question 5

What is the piezo electric effect?

Answer 5

Using crystals to convert mechanical energy into electrical energy.

Question 6

What is used to generate electricity from pressure.

Answer 6

Piezoelectric materials: crystalline materials, quartz.

Question 7

How is the voltage produced in a piezoelectric material?

Answer 7

When pressure is applied the voltage is produced by the changing charge created by the moving electrons

Question 8

What is used to generate electricity from heat.

Answer 8

Thermocouples

Question 9

How does a thermocouple operate?

Answer 9

By using 2 dissimiliar materials/conductors, iron and copper. that move the electrons from cold junction to the hot(iron) and then hot junction to cold (copper)

Question 10

What directly effects the thermoelectric voltage output of a thermocouple?

Answer 10

The difference in temperature between the hot and cold junctions.

Question 11

What are thermocouples mainly used for?

Answer 11

Measure temperature and used in heat sensing devices.

Question 12

What is used to generate electricity from light?

Answer 12

photovoltaic cell, photosensitive metal

Question 13

Explain photoelectric voltage

Answer 13

The photosensitive metal loses electrons from the lights intensity making it positively charged creating an electric force.

Question 14

Photosensitive materials most commonly used are?

Answer 14

various compounds of silver oxide or copper oxide

Question 15

What controls the amount of electrons emitted from the photo emissive material?

Answer 15

The intensity of the light source.

Question 16

Briefly describe the photoelectric cell process

Answer 16

Light is emitted onto the reflective photo emissive material, electrons are ejected off the material which move across to the anode, the electrons the move along a wire connected to the back of the photo emissive material where they replace the electrons getting ejected in the first step.

Question 17

What are the 2 purposes of the additional layers on the photoemissive material?

Answer 17

Permits penetration of light to copper oxide, collects electrons emitted by the copper oxide

Question 18

A primary cell produces an EMF only while the chemical reaction is in progress, once the chemical reaction is complete what happens to the Cell?

Answer 18

The primary cell is no longer usuable.

Question 19

The chemical reaction can be reset in a secondary cell what benefit does this have?

Answer 19

The secondary cell can be recharged, it is rechargeable.

Question 20

What is used in a wet cell?

Answer 20

The electrolyte is a liquid the cell must remain in an upright position and is not readily transportable.

Question 21

What is used in a dry cell?

Answer 21

It is not actually dry but mixed with an electrolyte to form a paste, it is the most commonly used battery.

Question 22

What is used to generate electricity from chemicals?

Answer 22

Requires a chemical or galvanic reaction, achieved by 2 dissimilar metals or substances immersed in a solution (electrolyte) which creates a greater chemical reaction on one side than the other. a potential difference between the 2 objects/bodies exists. a conductor can then be connected between the 2 metals externally allowing electron flow through the conductor which equalised the charge.

Question 23

What is the make up of a galvanic cell? (chemical reaction)

Answer 23

2 electrodes of dissimilar metals, an electrolyte and a container.

Question 24

How do you increase the electrical output of a battery?

Answer 24

Several cells are connected.

Question 25

What principle does a generator use to create electricity?

Answer 25

Electromagnetic induction.

Question 26

What are the 3 conditions that must exist to produce voltage from magnetism?

Answer 26

A conductor, a magnetic field in the conductors vicinity, relative motion between the field and the conductor.

Question 27

Which hand rule is used to view current direction in a generator?

Answer 27

Left hand rule

Question 28

which hand rule is used for a motor direction?

Answer 28

Right hand

Question 29

What creates electron flow in magnetism?

Answer 29

The movement of the conductor across the magnetic field, the conductor induces an EMF creating electron/current flow. you can reverse current flow by moving the conductor across the field in the opposite direction. (thumb rule but flipped upside down)

Question 30

What is the most common form of electric power generation?

Answer 30

Electromagnetic induction - A Conductor moving through the lines of magnetic flux of a magnet inducing electrons into the conductor.

Question 31

With magnetism what controls the amount of electricity produced and how can it be increased?

Answer 31

The rate at which the lines of flux are cut. increasing the number of flux lines by making the magnet stronger, or by moving the conductor faster.

Question 32

How does the magnetic field produce voltage?

Answer 32

The valence electrons are forced out of their atoms by the magnetic field causing electron flow.