Generators Flashcards
Define flux.
Magnetic material of force surrounding
Flux refers to the total magnetic field passing through a given area.
Define flux density.
Number of magnetic lines of force per unit area
Flux density quantifies the strength of the magnetic field in a specific area.
Define reluctance.
Opposition of a material to carry magnetic flux
Reluctance is analogous to electrical resistance in magnetic circuits.
Define residual magnetism.
Magnetic effect that remains in a material after the magnetizing force is removed
Residual magnetism is often a result of hysteresis in magnetic materials.
Define retentivity.
Level of ability of a material to retain residual magnetism
Retentivity is important for materials used in permanent magnets.
Define permeability.
The ability of a material to concentrate magnetic flux compared to a vacuum
Higher permeability indicates a material can support a higher magnetic field.
Define saturation.
Saturation is reached when any increase in magnetizing force will not produce an increase in magnetism within the material
At saturation, the material cannot be magnetized further regardless of the applied magnetic field.
Describe electromagnets.
The magnetic property of a conductor when current flows through it
Electromagnets are created by winding a wire into a coil and passing an electric current through it, generating a magnetic field.
What is a magnetic material?
Materials that are strongly attracted by magnets.
What are the two classifications of magnets?
- Temporary
- Permanent
What is a magnetic pole?
A region that attracts magnetic materials such as iron or steel.
Describe the two behaviours of the lines of force of a magnet.
- Take the easiest path between opposite poles
- They do not cross each other
Describe the two behaviours of magnetic poles when they are placed next to each other.
- Like poles repel each other
- Unlike poles attract each other
In what direction do the imaginary magnetic lines of force of a closed loop flow?
- From the north pole to the south pole
- From the south pole to the north pole
Which materials are strongly attracted by magnets?
Iron, nickel, cobalt
These are classified as ferromagnetic materials.
Which materials are only slightly attracted by magnets?
Platinum, aluminum
These materials are not as magnetic as ferromagnetic materials.
What are ferromagnetic materials?
Metals that are magnetized easily, such as iron, nickel, cobalt, manganese
Ferromagnetic materials exhibit strong magnetic properties.
What are paramagnetic materials?
Metals that can be magnetized but not as easily, such as platinum, chromium
Paramagnetic materials have weaker magnetic properties compared to ferromagnetic materials.
What are diamagnetic materials?
Metals and non-metals that cannot be magnetized, such as copper, brass, antimony
Diamagnetic materials repel magnetic fields.
What is magnetism?
A measurable characteristic of a moving electrical charge
Magnetism is fundamental to electromagnetic theory.
How are magnets classified?
- Temporary
- Permanent
This classification is based on their ability to retain magnetism.
What effect does decreasing the current in a conductor have on the magnetic field around the conductor?
Magnetic field decreases
This indicates an inverse relationship between current and magnetic field strength.
What happens to the magnetic field around the conductor if the current in a conductor is switched off?
Magnetic field around the conductor collapses
This indicates that the magnetic field is dependent on the presence of current.
When using the left-hand rule for conductors, what does the thumb indicate?
The thumb points in the direction of the electron flow in the conductor
This rule is a mnemonic to determine the direction of force in electromagnetic contexts.
If the electron flow is into the page, will the direction of the lines of force be clockwise or counterclockwise?
Counter clockwise
The direction of the magnetic field can be visualized using the right-hand grip rule as well.
What happens to the direction of the lines of force when the direction of the current flow is reversed?
The direction of the lines of force also reverses
This shows the direct correlation between current direction and magnetic field direction.
Indicate the north and south poles of the coils in Figure 24.
N
The specific orientation of poles is crucial for understanding magnetic fields in coils.
What three factors affect the strength of the magnetic field around a coil?
- Amount of current through the coil
- The number of turns on the coil
- The core material
These factors collectively determine the intensity of the magnetic field generated by the coil.
What effect does decreasing the current in a conductor have on the magnetic field around the conductor?
Magnetic field decreases
This indicates an inverse relationship between current and magnetic field strength.
What happens to the magnetic field around the conductor if the current in a conductor is switched off?
Magnetic field around the conductor collapses
This indicates that the magnetic field is dependent on the presence of current.
When using the left-hand rule for conductors, what does the thumb indicate?
The thumb points in the direction of the electron flow in the conductor
This rule is a mnemonic to determine the direction of force in electromagnetic contexts.
If the electron flow is into the page, will the direction of the lines of force be clockwise or counterclockwise?
Counter clockwise
The direction of the magnetic field can be visualized using the right-hand grip rule as well.
What happens to the direction of the lines of force when the direction of the current flow is reversed?
The direction of the lines of force also reverses
This shows the direct correlation between current direction and magnetic field direction.
Indicate the north and south poles of the coils in Figure 24.
N
The specific orientation of poles is crucial for understanding magnetic fields in coils.
What three factors affect the strength of the magnetic field around a coil?
- Amount of current through the coil
- The number of turns on the coil
- The core material
These factors collectively determine the intensity of the magnetic field generated by the coil.
What happens to the strength of the magnetic field when electricity is applied?
The strength of the magnetic field decreases
This is based on the relationship between electric current and magnetic field strength.
Why is silicon steel used to make cores for coils?
Cores made of silicon steel reduce hysteresis losses
Silicon steel has properties that minimize energy loss during magnetization.
Name two types of iron loss that can occur in the core of an electromagnet.
- Eddy currents
- Hysteresis
Eddy currents are loops of electric current induced within conductors by a changing magnetic field.
Why are iron coil cores laminated?
To reduce eddy current losses
Laminating the core helps to interrupt the paths for eddy currents.
Define hysteresis.
The heat produced due to the lagging of magnetic domains in an iron core
Hysteresis represents energy loss when the magnetization of a material lags behind the applied magnetic field.
When are eddy currents produced?
When a magnetic core is subjected to a changing magnetic field
This occurs due to Faraday’s law of electromagnetic induction.
When does the core of an electromagnet become saturated?
When an increase in current in the coil does not produce an increase in magnetism in the core
Saturation occurs when all magnetic domains are aligned and cannot align further.
What is faradays law of induction?
When there is change in a magnetic field within a closed loop it induces an EMF in the conductor
