Electromagnetism Flashcards
Definitions from AH unit 3
What is meant by “Electrostatic force”?
The force experienced between two charged objects. The force is proportional to the magnitude of the charges, and inversely proportional to the square of the radius between them.
What is meant by “Electric field strength”?
The force experienced by a unit positive (+1C) charge at that point in the electric field.
What is meant by “Electrostatic potential”?
The work done to bring a unit positive charge from infinity to a point in an electric field.
What is meant by 1 “Electron-Volt”?
The work done to move a charge of 1 electron through a Voltage of 1V.
What is meant by “Potential difference”?
The work done to move a unit positive charge between two points.
What is meant by the “Time constant” of a charging capacitor?
Time taken by the capacitor for the charge stored to increase to 63 % of its full value when charging.
What is meant by the “Time constant” of a discharging capacitor?
Time taken by the capacitor for the charge stored to reduce to 37 % of its full value when discharging.
What is the relationship between current and frequency of an AC resistor circuit?
No relationship - varying the frequency does not affect the current.
What is the relationship between current and frequency of an AC capacitor circuit?
The frequency and current are directly proportional to each other.
What is meant by “Capacitive reactance”?
The opposition of a capacitor to changing current
What is meant by a “Ferromagnetic” material?
In a ferromagnetic material the magnetic domains in the material can be made to align, resulting in the material becoming magnetised.
State a method to demangetise a ferromagnetic material.
- “Hammer” the Metal - The mechanical jarring can randomise the domains.
- Apply a high frequency alternating magnetic field across the metal - the high frequency alternation causes the domains to randomise.
- Raise its temperature above its Curie Temperature - the increased kinetic energy within the crystal structure randomises the domains.
State a ferromagnetic material
- Iron
- Nickel
- Cobalt
What is meant by “Electron flow” in terms of current?
The flow of negatively charged electrons. The correct way for current to flow in Scotland, and what is actually happening in a circuit.
What is meant by “Conventional flow” in terms of current?
The flow of positive charges. Traditionally taught in all English speaking regions apart from Scotland. Not what is actually happening in a circuit.
Which type of current flow applies to “Fleming’s right hand” rule?
Electron flow (negative charge)
Which type of current flow applies to “Fleming’s left hand” rule?
Conventional flow (positive charge)
What is meant by the “Magnetic induction” of 1 Tesla?
1 Tesla is the magnetic induction in which a conductor of 1 metre of length with a current of 1 ampere perpendicular to the field is acted on by a force of 1 Newton.
What is meant by a current of “1 Ampere”?
The constant Current which, if in two straight parallel conductors of infinite length placed one meter apart in a vacuum, will produce a force between the conductors of 2 x 10-7 newtons per meter.
How does a magnetic field affect a charge moving parallel to the field?
No effect, particle will travel in a straight line at a constant speed.
How does a magnetic field affect a charge moving perpendicular to the field?
The particle will experience a force at right angles to its motion, causing the particle to follow a circular path.
How does a magnetic field affect a charge moving at an angle to the field?
Two velocity components combine to given Helical motion.
v sin θ - Circular motion perpendicular to the Magnetic field B
v cos θ - Straight line motion in the direction of the Magnetic field B
What is meant by the “Pitch” of a helical motion?
The distance traveled in the direction of the Magnetic field B during one Period of Rotation.
What is meant by “Self inductance”?
The induced EMF within a conductor caused by its own changing magnetic field.
What is meant by “Back EMF”?
The self induced EMF within a conductor caused by its own changing magnetic field. The Back EMF acts to oppose the change that produced it.
What is meant by an “Inductance” of 1 H?
The Inductance of an Inductor across which an EMF of 1 Volt is induced when the Current in the conductor changes at a rate of 1 Ampere per second.
Why could a spark be produced when the contacts of a switch are opened?
When an Inductor is turned off, the magnetic field rapidly collapses, generating large Back EMFs. These large Back EMFs can cause sparks across the open contacts of the switch. The energy required to create the spark was stored in the magnetic field.
What is the relationship between current and frequency of an AC inductor circuit?
The frequency and current are inversely proportional to each other.
What is meant by “Inductive reactance”?
The opposition of an inductor to changing current.
What is meant by “Impedance”?
The overall opposition to current flow, regardless of component type.
