# Shared Flashcard Set

## Details

Ch 20 Magnetism
concepts and formulas
29
Physics
03/22/2013

Term
 Magnets have two ends called ?
Definition
 poles;  North & South
Term
 Like poles ______  unlike poles _______
Definition
 1.repel 2. attract
Term
 Magnetic fields can be visualized using _____ which are always _______
Definition
 1.magnetic field lines 2.closed loops
Term
 magnetic field lines always go from  ____ to ____
Definition
 North to South.
Term
 True or False: the Earth’s “North Pole” is really a south magnetic pole
Definition
 True:  the north ends of magnets are attracted to it.
Term
 A uniform magnetic field is constant in (2)
Definition
 magnitude & direction
Term
 Experiment shows that an ______ produces a magnetic field
Definition
 electric current
Term
 Given that Electric Currents Produce Magnetic Fields, what rule can we use to the find the direction of the magnetic field?
Definition
 right-hand rule
Term
 A magnet exerts _____ on a current-carrying wire. The direction of the force is given by a right-hand rule
Definition
 a force
Term
 the Force on an Electric Current carring wire due to a Magnetic Field, formula
Definition
 F= IlB sin θ   this means the force on the wire depends on: the current (I), the length of the wire (l), the magnetic field (B)  its orientation .
Term
 If the direction of I is perpendicular to B, then θ is?  sin θ ?
Definition
 θ :90   sin θ: 1
Term
 If I (the current) is parallel or antiparallel to B, then θ= ____ and sin θ = ____.
Definition
 θ = 0˚   sin θ = 0 This equation defines the magnetic field B. the force is zero
Term
 Magnetic Field, Unit of B
Definition
 the tesla, T. 1 T = 1 N/A·m. Another unit sometimes used: the gauss (G). 1 G = 10-4T.
Term
 The direction of a force on a electric current in a magnetic field is always
Definition
 perpendicular to the direction: of the current & magnetic field
Term
 if the magnetic field is stronger then the force will be ____
Definition
 stronger
Term
 True or False: b/c a current carrying wire experiences a force when placed in an electric field, 1.can moving charged particles not in a wire experience a force when moving through a magnetic field?   2.When is this force the greatest?
Definition
 1.yes 2. when the particle moves perpendicular to the electric field (B)   θ= 90
Term
 A moving charge feels a force of zero when?
Definition
 when the particle moves parallel to the magnetic field lines   θ = 0
Term
 A negative charge -Q is placed at rest near a magnet. Will the charge begin to move? Will it feel a force? What if the charge were positive, +Q?
Definition
 No to all questions. A charge at rest has a velocity  of zero. Magnetic fields excert a force only on moving electric charges
Term
 The force on a moving charge : formula
Definition
 F= qvB sinθ
Term
 If a charged particle  (electron or proton) is moving perpendicular to a uniform magnetic field, its path will be?
Definition
 circular
Term
 What is the path of a charged particle if its velocity is not perpendicular to the magnetic field?
Definition
 The parallel component of v experiences no force, so it remains constant.  The perpendicular component of v results in circular motion.  Together this produces a spiral motion.
Term
 what is a solar wind?
Definition
 Charged ions that approach the Earth from the sun (solar wind) and are drawn toward the poles.  This causes the Northern lights.
Term
 Magnetic Field Due to a Long Straight Wire: the magnetic field strenghth is greatest at a given point when
Definition
 if the current flowing in the wire was greater
Term
 Magnetic Field Due to a Long Straight Wire: the magnetic field strenghth is weaker at  points
Definition
 farther from the wire
Term
 Force between Two Parallel Wires : Parallel currents _____  antiparallel currents ___ attract or repel
Definition
 1.attract 2.repel
Term
 Solenoids and Electromagnets: If a piece of iron is inserted in the solenoid, the magnetic field (increases or decreases)?
Definition
 greatly increases
Term
 How does a solenoid work?
Definition
 a solenoid is a long coil of wire with many loops.  each loop produces a magnetic field and the total field in the solenoid will be the sum of the fields due to each current of each loop.
Term
 Describe the magnetic field inside the solenoid if it contains a large number of loops and are closed packed?
Definition
 the magnetic field is nearly constant.
Term
 Describe the magnetic field outside the solenoid
Definition
 the field lines spread out in space, so the magnetic field is much weaker outside the solenoid than inside the solenoid.
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