RAD Physics - Chapter 8: Electromagnetism

magnetic field

Surrounding every wire carrying a current there exists a _____ (temporary)

current

Magnetic field only exists while __ is flowing through the wire

Left thumb rule

used to determine the direction of the magnetic field around the wire

wrap hand around wire, point thumb in direction of current, then your fingers wrap around the direction of the magnetic field (either clockwise or counterclockwise)

*Know how to do left thumb rule*

either clockwise or counterclockwise

what are the 2 possible answers for the left thumb rule?

1. Helix

2. Solenoid

3. Electromagnet

what are the three types of electromagnets?

locks in the x-ray machines

What are solenoids used in?

Found in remote control switches and relays in our x-ray equipment

What are electromagnets found in?

Relay

switch that activates another switch?

1. look for negative side

2. wrap left hand around coil

3. thumb direction = north pole

How to do horizontal left thumb rule?

to the reader’s right or to the reader’s left

What are the 2 possible answers for the horizontal left thumb rule?

Electromagnetic induction

how magnetic fields can create (induce) current flowing in a wire

Flux linkage

each time a wire intersects a magnetic line of flux

potential difference(EMF)

Any time a conductor cuts across magnetic flux or is cut by magnetic flux, a ___ is induced in a wire

magnetic lines of flux

Flux lines or ___ mean the same thing

the number of flux linkages per second

Size of the induced emf is dependent upon ____

increases

As the number of flux leakages per second (speed) increases, the magnitude of the induced emf ____

increases

As strength of magnetic field increases, the magnitude of the induced emf ___

higher

As the angle between the conductor and direction of the magnetic field approaches 90 degrees, the ___ the induced emf (maximum flux leakages per second)

increases

As the number of turns in the coil increases, the magnitude of the induced emf ___

Three ways to induce voltage in a wire by electromagnetic induction (to get a flux leakage):

1. Wire moves, but stationary lines of flux

2. Wire stationary, but magnetic flux moves across wire

3. A magnet (magnetic flux varies in strength) can vary in strength, while a stationary wire lies within it

Left Hand Rule

answers the question which way the current flows (direction)

towards the reader or away from the reader

What are the 2 possible answers for the left hand rules?

1. Index: south pole

2. Thumb: up or down

3. Middle: direction of current

Dynamo Rule: (which do each of these do?)

1. Index?

2. Thumb?

3. Middle?

electromagnetism

The branch of physics that deals with the relationship between electricity and magnetism is called __________

magnetic field (temporary)

A __________ surrounds a conductor carrying an electric current

current, magnetic field

According to the left thumb rule, if a wire is held in the left hand with the thumb pointing in the direction of the __________, the fingers grasping the wire will indicate the direction of the _________

helix

A wire coil is called a __________.

north pole, south pole

When a current flows in a wire coil, one end of the coil behaves as the __________ and the other end as the __________.

current flow, north pole

To determine which end of the coil is the north pole and which end is the south pole, wrap the fingers of the left hand around the wire in the direction of the __________. The thumb will then point in the direction of the __________.

solenoid

A helix carrying an electric current is called a __________.

electromagnet

A solenoid with an iron core is called an __________.

electromagnetic induction

Magnetic fields can induce electric currents in a process known as __________.

magnetic flux, magnetic flux

Whenever a conductor cuts across __________ or is cut by __________, an electromotive force, or potential difference is induced in the conductor.

flux linkage

Interaction between a magnetic line of force and a conductor is called a __________.

increases

As the number of flux linkages per second increases, the magnitude of the induced emf __________.

increases

As the strength of the magnetic field increases, the magnitude of the induced emf __________.

90 degrees

As the angle between the conductor and direction of the magnetic field approaches __________ degrees, the higher the induced emf.

increases

As the number of turns in the coil increases, the magnitude of the induced emf __________.

magnetic flux, conductor movement, induced electric current

According to the left hand rule, if the thumb and first two fingers of the left hand are held so that each is at a right angle to the others, and the index finger points in the direction of the ___________, the thumb points in the direction of __________, then the middle finger will point in the direction of the __________.

self-induction

If an open switch in a direct current circuit containing a coil is closed, an emf will be induced in the coil in the opposite direction of the applied emf. This process is known as __________.

magnetic field

During self induction, when the switch is first closed, a __________ builds up around the coil, causing an induced emf that opposes the direction of the applied emf.

falls to zero

When the switch is closed, the magnetic field is constant and does not move relative to the coil. The self induced emf __________.

reverses direction + maintains the current in coil momentarily after the switch has been opened

If the switch is then opened, the magnetic field collapses across the coil in the reverse direction. The self induced emf __________.

“make”

Closing the switch is referred to as __________.

“break”

Opening the switch is referred to as __________

mutual induction

Placing a pair of insulated wire coils side by side and applying an alternating current to one will induce an emf in the other in a process called __________.

locks

Where are solenoids found in the x-ray machine?

remote control switches + relays

Where are electromagnets found in the x-ray machine?

1. The wire moves across a stationary magnetic flux.

2. The magnetic flux moves across a stationary wire.

3. The magnetic flux may vary in strength while a stationary wire lies in it

List three ways to induce voltage in a wire by electromagnetic induction.