Electricity Flashcards
What occurs in the battery with electrons and protons
Negative terminal in the battery with an abundance of electrons that want to move to the positive terminal as they have protons with a lack of electrons.
What is the terminology of current (Amperes) and Voltage (Volts) and Resistance
Current - the rate that electrons (electricity) flows past a point in a circuit
Voltage - the potential difference in charge between two points in an electrical field
Resistance - how much something opposes current passing through it. (Height of a water fall, higher the waterfall the more potential energy the water has and the more energy it will have when it hits the bottom)
What is typically the flow of electrons and protons and what is it in batteries?
Positive (protons) to electrons but in a battery the opposite due to the negative terminal having a lack of electrons
What is ohms law
Voltage = amperage x resistance
Explain the basic characteristics of an electrical circuit.
If a circuit is not complete, current will not flow.
Describe the structure of a:
(a) two-wire circuit;
(b) grounded ‘earth return’ electrical circuit.
(A) Electrical circuit consists of some form of generator, a load which uses electricity and conductors that are connect the two and a switch for control.
Open circuit means current will flow. Closed is opposite
(B) grounded circuits are used to save wire and reduce weight. In a grounded circuit, the metal part of aircraft is used as a conductor.
Distinguish between direct and alternating current.
DC - flow of electric current in a single direction, used for control circuits and emergency backup supply
AC - current changes direction, which is produced by an alternating current such as a Alternator.
Explain the terms:
(a) frequency (Hertz);
(b) rectification.
Frequency - number of cycles per second measured in Hertz
Rectification - change of AC to DC
Explain the properties of magnetism, including:
(a) polarity;
(b) attraction;
(c) repulsion
Polarity - the attractive force the aligns magnetic items and aligns itself parallel with the lines of the earths magnetic field
Attraction - unlike charges attract (N-S)
Repulsion - like charges repel (N-N)
Distinguish between:
temporary and permanent magnets;
the properties of ‘soft iron’ and ‘hard iron’ magnets.
Temporary - known as soft iron which are susceptible to being magnetised but have poor retentivity
Permanent - known as hard iron, low susceptibility, high retentivity
Describe the terms:
(a) magnetic field;
(b) magnetic flux;
(c) permeability.
Magnetic field - space around a magnet in which its influence can be detected.
Made up of lines of magnetic force which represent the direction in which a magnetic North Pole would move if free to do so.
Magnetic flux - number of magnetic lines of force set up in a magnetic circuit.
Permeability - resistance of a material against the formation of a magnetic field
What are the properties of magnetic flux (4)
Always form a closed loop
Always start north end south
Never intersect
Magnetic lines of forces that are the same (south and south) repel
Explain electromagnetism.
It is the strength of a magnetic field thats proportional to the amount of current flowing .
Describe the lines of magnetic force around a;
(a) straight conductor;
(b) current carrying coil.
(A) when current flows in a wire, a magnetic field is formed around the wire, if the wire is straight, the field will form around the wire (Right hand rule)
(B) when current flows in a coiled wire, magnetic field is formed around the wire.
Describe the construction and the principle of operation of an electromagnetic switch (relay and solenoid)
RELAY
Consists of an electromagnet ( coil around soft iron core) and a pivoting arm of soft iron called armature.
When electromagnet is energised, contact points are closed and current flows through the circuit, and when contact opens when control switch is off the magnetism is gone.
SOLENOID
Same build. When coil is energised a soft iron plunger is magnetically attracted into the coil and the contact disc bridges contact and closes circuit.
Describe typical examples of the use of electromagnetic switches in aircraft electrical circuits.
Battery solenoids - when you turn master switch on
Starter solenoid - low amperage, which then allows a higher current to operate the starter motor
Battery to master solenoid to bus bar to starter switch to starter solenoid to starter motor.
Explain the principle of electromagnetic induction and the requirements
the creation of an electromagnetic field in a conductor by means of of magnetism.
Requirements:
A magnetic field (magnet)
Conductor (wire coil)
Movement between them
And the voltage produced will depend on the strength of the magnet and speed of movement.
Describe the principle of operation of a simple alternator.
An alternator produces electricity via electromagnet induction, If you turn a magnet inside a coil of wire, you will make electricity this is referred to as an alternator
Describe:
(a) the features of a practical alternator;
A practical alternator uses an electromagnet (“rotor”) spinning inside a stator (made of coils of wire)
For the alternator the electromagnet requires power to excite and can only get this from the battery.
Dead battery means it wont work
Describe how the AC output is normally rectified to provide DC and why
Natural output of the alternator is AC, aircraft require DC.
Rectification is done by diodes to become DC.
Describe the principle of operation of a simple generator.
Generators rotate a coil of wire (rotating loop) inside a magnet which generate AC.
Describe:
the features of a practical generator;
how the output is passed through a commutator to provide DC
Features - rotating loop conductor which is made to rotate within a magnet where the magnetic field created is stationary.
Output - fitting a commutator (a ring with gaps inside into the generator which inverts the AC into DC
Explain:
(A) the need for voltage regulation for both alternators and generators;
(B) why a generator also requires a current regulator and a reverse current relay
(A) if voltage output is too high from an alternator or regulator, this will cause damage to the items and the electrical systems
(B) current regulator - regulates the amount of Current flow. When electric loads are high and battery is low, current regulator will prevent the generator output from exceeding its safe maximum.
Reverse current relay - stop current form the battery discharging back into the battery.
Explain the principle of operation of a battery.
A battery produces electricity via a chemical reaction.
Done by the electrolytes reacting with the electrodes, causing electrons to be attracted to the negative terminal.
