El Thoery Flashcards
Explain electrical current
The movement of free electrons along a conductor
Explain electron flow
Negative to positive , -ve to +ve
Explain Conventional current flow
Positive to negative, +ve to -ve
Explain ampere
• the unit of measurement of current
•ampere - A
•the amount of electron passing a given point in one second
1 amp= 6.241 x 10 (18)
Circuit symbol for current
I
What are the Effects of current flow
Causes heat and sets up a magnetic field around a conductor
Potential difference
Exits between two points in a circuit having a difference in charge
What is EMF ?
Electromotive force - the force that drives the current around a circuit
Explains voltage
•Is pressure which causes current flow
•basic unit of measurement of voltage is the volt.
•circuit symbol for voltage is v
Voltage production methods
Chemical
Friction
Induction
Pressure
Heat
Light
What does Voltage produced through induction - three prerequisites are needed
• an electrical conductor
• A magnetic field
•relative motion
What can produced voltage by pressure
Piezo quartz crystal
Voltage produced by heat
Thermocouple
Voltage produced by light
•artificially manufactured materials
• semiconductors
•solar panels
What is a conductor
A material many free electrons, will pass current freely
What is a insulator
A material having few free electrons, will only pass current with great difficulty
What is resistance?
• opposition to current flow
•basic measurement of resistance is the ohm
•it’s symbol is omega
Insulators
Wood
Paper
Rubber
Mica
Insulating varnish
Porcelain
Plastic
Woven fabrics
Glass
Conductors
Copper
Brass
Silver
Carbon
Impure water
Aluminium
Platinum
Mercury
Gold
Factors affecting resistance
Type of materials - insulator or conductor
Length of conductor - double the length - double resistance…. Half the length -half the resistance.
The cross sectional area can - large csa - low resistance……… small csa - high resistance.
Temperature - hotter/ cooler - resistance higher/lower
Ohms law
That a current flowing through a conductor is directly proportional to the applied voltage across it. Providing the temperature remains constant, and is inversely proportional to to the resistance.
What is the definition of power
Power is the rate of doing work
Mechanical power formula = force x distance/time
Electrical power depends on which two items
• current - the number of electron to be moved
•emf( voltage ) -the rate at which the electrons are made to travel.
What is 1hp in watts
746w
What is electrical unit of power?
Watt (w)
What is the mechanical unit of power
Horsepower (hp)
Earth faults are caused by low resistance between the current carrying conductors and earth. This occurs when the insulator resistance of the circuit wiring decreases.
What are the main causes of this,
•dampness
•insulation becoming hard or brittle with age or heat
• accidental damage
Why is equipment earthed
•safeguards against shocks
How does earthing work?
Current would flow through the earth conductor( ship’s hull) and because it has low resistance this would stole the person getting a shock.
What is a fuse link ?
Main common type of fuse in the Royal Navy operates the same as a cartridge fuse.
What is a cartridge fuse
A fuse wire in a cylinder of insulating heatproof material
What is the disadvantages of a cartridge fuse ?
A voltage could arc even after the fuse has blown.
What is a hrc fuse?
High rupturing capacity fuse
What insulator is used within a hrc fuse
Quartzs
What are the minute particles called that all matter is mad up of?
Atoms
In an atom what is the name of the element that revolves around the nucleus
Electrons
What part of the atom has no charge
Neutron
Which part of the atom has a negative charge
Electron
Which part of the atom has a positive charge
Proton
What is meant by the term “ a balance atom”
Equal amount of electron neutrons and protons
In a atom what holds the electrons in orbit of nucleus
Force of attraction
What is an electron know as once is has been forced out of orbit of an atom
Free electron
What is the name given to the electron furthest away from the the nucleus
Valence electron
What is the outer shell of an atom know as
Valence she’ll
In certain material very little energy is need to force electrons out of orbit and enable current flow. What are these material know as
Conductor
In a basic secondary cel, what charge does the plate have that has lost its electron
Positive charge
What is the liquid called that allows electrons
Electrolyte
With reference electron flow what direction do electrons travel in a circuit
From negative to positive
With reference to conventional current flow what direction do electron travel in a circuit
Positive to negative
What is the name given to current flow that goes from the positive to negative charge
Conventional flow
What the name given to the force that drives current around a circuit
Voltage
