3.4 Generation of Electricity Flashcards
How is static electricity generated?
Via friction between two insulating materials rubbing together.
How do you find out which materials become positive and which negative when rubbed together?
Triboelectric chart, Higher on the chart = positively charged (loses electrons), lower on chart = Negatively charged (gains electrons)
Aircraft utilise static dischargers and position them where?
To minimise interference with radio systems where friction can pick off the positive or negative charge.
How do crystals (quartz) generate voltage?
When ever stresses are applied to their surfaces: pressure, squeezed.
What is the piezo electric effect?
Using crystals to convert mechanical energy into electrical energy.
What is used to generate electricity from pressure.
Piezoelectric materials: crystalline materials, quartz.
How is the voltage produced in a piezoelectric material?
When pressure is applied the voltage is produced by the changing charge created by the moving electrons
What is used to generate electricity from heat.
Thermocouples
How does a thermocouple operate?
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)
What directly effects the thermoelectric voltage output of a thermocouple?
The difference in temperature between the hot and cold junctions.
What are thermocouples mainly used for?
Measure temperature and used in heat sensing devices.
What is used to generate electricity from light?
photovoltaic cell, photosensitive metal
Explain photoelectric voltage
The photosensitive metal loses electrons from the lights intensity making it positively charged creating an electric force.
Photosensitive materials most commonly used are?
various compounds of silver oxide or copper oxide
What controls the amount of electrons emitted from the photo emissive material?
The intensity of the light source.
Briefly describe the photoelectric cell process
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.
What are the 2 purposes of the additional layers on the photoemissive material?
Permits penetration of light to copper oxide, collects electrons emitted by the copper oxide
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?
The primary cell is no longer usuable.
The chemical reaction can be reset in a secondary cell what benefit does this have?
The secondary cell can be recharged, it is rechargeable.
What is used in a wet cell?
The electrolyte is a liquid the cell must remain in an upright position and is not readily transportable.
What is used in a dry cell?
It is not actually dry but mixed with an electrolyte to form a paste, it is the most commonly used battery.
What is used to generate electricity from chemicals?
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.
What is the make up of a galvanic cell? (chemical reaction)
2 electrodes of dissimilar metals, an electrolyte and a container.
How do you increase the electrical output of a battery?
Several cells are connected.
What principle does a generator use to create electricity?
Electromagnetic induction.
What are the 3 conditions that must exist to produce voltage from magnetism?
A conductor, a magnetic field in the conductors vicinity, relative motion between the field and the conductor.
Which hand rule is used to view current direction in a generator?
Left hand rule
which hand rule is used for a motor direction?
Right hand
What creates electron flow in magnetism?
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)
What is the most common form of electric power generation?
Electromagnetic induction - A Conductor moving through the lines of magnetic flux of a magnet inducing electrons into the conductor.
With magnetism what controls the amount of electricity produced and how can it be increased?
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.
How does the magnetic field produce voltage?
The valence electrons are forced out of their atoms by the magnetic field causing electron flow.
