Unit 7 -Magnetism

Question 1

Kirchhoff’s current law

Answer 1

the total amount of current into a junction point of a circuit equals the total current that flows out of that same junction
relates to the law of conservation of charge

Question 2

Kirchhoff’s voltage law

Answer 2

the total of all electricity potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop
relates to the law of conservation of energy

Question 3

Magnetism (magnetic field, ferromagnetic metal, electromagnet, solenoid, retentivity)

Answer 3

magnetic field = distribution of a magnetic force in the region of a magnet
ferromagnetic metal = metals such as iron, nickel, and cobalt, or mixtures of these three that attract magnets
electromagnet = coil of wire around a soft iron core, which uses electric current to produce a magnetic field
solenoid = a coiled conductor that acts like a magnet when current is passed through it
retentivity = ability of a magnet to stay magnetized

Question 4

Law of magnetic forces

Answer 4

similar magnetic poles repel one another with a force at a distance
dissimilar poles attract one another with a force at a distance

Question 5

Field lines

Answer 5

field lines of a magnetic field show the direction in which the north seeking pole of a test compass would point at that point in space

Question 6

Domain theory

Answer 6

all large magnets are made up of many smaller and rotatable magnets, called dipoles, which can interact with other dipoles close by
if dipoles line up, then a small magnetic domain is produced

Question 7

Magnetic induction

Answer 7

ferromagnetic materials can be magnetized, such as the Earth magnetizing railroad tracks
explanation = domains that are pointing in random directions can be aligned if they are placed in a large field with a fixed direction

Question 8

Demagnetization

Answer 8

ferromagnetic materials can lose their magnetic strength
explanation = domains could lose their order and point in different directions causing a dilution and overall weakening of the magnet

Question 9

Reverse magnetization

Answer 9

the polarity of magnets can be reversed
explanation = a large magnetic field pointing in the opposite direction causes all the domains to line up with the new field, reversing the overall magnetic polarities

Question 10

Breaking magnets

Answer 10

it is possible to break a larger magnet into smaller ones

explanation = in all the pieces, the domains still line up, so each acts like its own magnet

Question 11

Maximum strength

Answer 11

a magnet can become only so strong and no more

explanation = once all the domains are aligned, there is no way to increase the magnet’s strength any further

Question 12

Oersted’s principle

Answer 12

a charge moving through a conductor produces a circular (cylindrical) magnetic field around the conductor

Question 13

Magnetic field around a straight conductor

Answer 13

direction of magnetic field = direction a north pole would go
around a straight conductor, the magnetic field is represented by concentric circles
in a straight conductor, there are no poles
left hand rule = if a conductor is held in the left hand with the left thumb pointing in the direction of electron flow, then the curled fingers will point in the direction of the magnetic field lines

Question 14

Magnetic field around a solenoid

Answer 14

the magnetic field outside a solenoid shows the same pattern outside a bar magnet
left hand rule = if a coil is grasped in the left hand with the added fingers representing the direction of electron flow, the thumb points towards the north pole of the magnetic field

Question 15

Factors affecting magnetic field strength

Answer 15

current = direct variation
number of turns in the solenoid = direct variation
diameter = inverse variation
core material = direct variation with the magnetic permeability (a coefficient that multiplies the field strength)

Question 16

The motor principle

Answer 16

a conductor in which electrons are moving perpendicular to an external magnetic force experiences a force that is perpendicular to the conductor, and the magnetic field lines
left-hand rule = when the fingers of the left hand point in the direction of the external magnetic field, and the thumb represents the direction of electron flow, the force on the conductor will be the direction in which the palm faces

Question 17

Direct current motor (field magnet, solenoid, commutator, brush, armature)

Answer 17

field magnet = provides external magnetic field
solenoid = provides the second magnetic field which reverses polarity
commutator = reverses current direction every 180 degrees
brush = stationary, provides electrical contact between power supply and commutator
armature = rotates

Question 18

Faraday’s law

Answer 18

a magnetic field that’s moving or changing intensity near a conductor causes electrons to flow in the conductor

Question 19

Lenz’s law

Answer 19

the direction of the induced current is such that its magnetic field opposes the actions of the inducing magnet

Question 20

Transformers

Answer 20

transformers use electromagnetic induction and alternating current to raise or lower the potential difference in a system
an alternating current is required because as the electrons in the primary coil go back and forth, the magnetic field induced in the iron ring is constantly reversing polarity
this induces an alternating current in the secondary coil
for long distance transmission, less energy is lost if the current is low

Question 21

Electromagnetism

Answer 21

like gravity, electrical and magnetic fields are examples of a force at a distance
no contact is required