Physics Chapter 24 Magnetic Fields
Terms in this set (70)
describes the property of having two distinct, opposite ends, one of which is a north seeking pole and other of which is a south seeking pole
the area around a magnet, or around any current-carrying wire or coil of wire, where a magnetic force exists
the number of magnetic field lines that pass through a surface
first right-hand rule
a method used to determine the direction of the magnetic field relative to the direction of the conventional current
a long coil of wire with many loops; fields from each loop add to the fields of the other loops, creating a greater total field strength
a magnet created when current flows through a wire coil
second right-hand rule
a method used to determine the direction of the field produced by an electromagnet, relative to the flow of the conventional current
a very small group, usually 10-1000 u, that is formed when the magnetic fields of the electrons in a group of neighboring atoms are aligned in the same direction
third right-hand rule
a method that can be used to determine the direction of the force on a current-carrying wire in a magnetic field
a device that is used to measure very small currents; can be used as a voltmeter or an ammeter
the wire coil of an electric motor, made up of many loops mounted on an axle or shaft; torque on an armature, and the motor's resultant speed, is controlled by varying the current through a motor
What did the Chinese invent and use for navigation?
compass / lodestone
What is a compass?
a small magnet, mounted so that it is free to turn and responds to earth's magnetic field
What happens if your break a magnet in half?
You create two separate magnets with each having two poles
what are monopoles?
separate north and south poles
What is Earth?
Earth itself is a giant magnet
What does a compass north point and the south magnetic pole of the Earth point to?
Compass north points north
- South magnetic pole points to north geographic pole
When a magnet is attached to the object then the object...?
Many permanent magnets are made up of ...
iron alloy called ALNICO V (Al, Ni, Co)
What does it mean to be ferromagnetic?
strongly attracted to magnets
Do magnets have to touch each other in order to experience a magnetic force?
No and only the magnetic fields need to touch for a magnetic force to be exerted
What helps visualize the magnetic field and measure the strength of the field
the magnetic field lines
The magnetic field lines always form from...
south to north pole to create loops
Who was the physicist that experimented electric currents with wires? and what did he find??
`- Hans Christian Oersted
- He found that the forces on the compass magnet's poles were perpendicular to the direction of current in the wire
Is the direction of the field lines is direct to the current??
in the first right hand rule, what does the thumb indicate and what do the other fingers indicate?
- fingers: direction of magnetic field
The direction of the field inside the loop is always the
the more loops of coils causes
a stronger field strength
The strength of the field is ..... to the current of the coil
an electromagnet can also be increased by placing .... inside the coil
an iron rod or core
In a second right hand rule what does the finders indicate, what does the thumb indicate?/
thumb- direction of magnetic field (north pole)
- fingers: direction of magnetic field
Each electron in an atom acts like....
A tiny electromagnet
When an iron is not in a magnetic field??
the domain is in random order
Recorders are made up of electromagnets and when magnetic recording tape passes over a recording head??...
- The domains are aligned and
Rocks containing iron have recorded the history of the varying directions of Earth's magnetic field
direction of magnetic field b/w two magnets is..
from north to south pole
In the third right hand rule what does the thumb, fingers, and palm indicate??
Fingers- point in direction of magnetic field (south pole)
- thumb is the direction of the conventional current(positive)
-palm- faces the direction of the force acting on the wire
When currents are in opposite directions...?
the wires have repulsive force between them
What is the formula for force on a current-carrying wire in a magnetic field?
F = ILB
- B= strength of the field
What is B measured in??
1 T = 1N /A.m
what happens if the wire is not perpendicular??
What does a loudspeaker do?
changes electric energy to sound energy
A galvanometer can also be connected as...?
when is the meter calibrated...?
how much coil turns when a known current is sent through it
What does a picture tube use???
uses electrons deflected by magnetic fields to form pictures
Force of a magnetic field on a charged, moving particle
Magnetic fields exit from...?
the north pole of a magnet and enter its south pole
magnetic field lines always form..
a coil carrying a current has...
a magnetic field
the field about the coil is like the field about a...
the strength of the magnetic field is measured in
when a current carrying wire is placed in a magnetic field...?
there exists a force on the wire, perpendicular to both the field and wire
The force on a current-carrying wire in a magnetic field is proportional to...
the field strength, the current flow, and the length of the wire
a galvanometer can be used as an ammeter by..
adding a shunt resistor in parallel with the galvanometer
a galvanometer can be used as a voltmeter by
adding a multiplier resistor in series
A loudspeaker functions by...
varying the current through a coil that is placed in a magnetic field. The coil is attached to a paper cone that moves when the coil moves
- cone vibrates which later produces sound
An electric motor can rotate
360 by using a commutator to switch the direction of the current in the coil as the coil rotates
the force that magnetic field exerts on a charged particle depends on three factors
- the velocity
- strength of the field
The north pole of a compass needle is attracted to..
Earth's south magnetic pole
which objects are magnetic??..
Paper clip, nail, razor blade, straight pin
ferromagnetic elements have..
many unpaired electrons spinning in the same direction, to produce identical magnetic fields
most common ferromagnetic elements..
Fe , Co, Ni
What will happen when a magnet becomes heated?
will weaken it and lose the alignment of the domains b/c there is more disorder
what is magnetic indcution
the process of generating a current in a circuit by changing a magnetic field
to increase the strength of the magnetic field is to...
increase number of coil and amount of electricity flowing through the wire
whats an electric generator??
converts mechanical to electricity
- armature rotates in a strong magnetic field to induce a current
what is Lenz's Law
Induced current opposed the motion that induces it
- Work must be done to overcome the magnetic repulsion
Whats a electric motor?
has same parts as generator
- converts electrical into mechanical
- current moves through armature inside a magnetic field making armature turn