Electromagnetism Flashcards
What is a magnetic field?
the region around a permanent magnet or a moving charge (an electric current) in which another body with magnetic properties will feel a force
What do magnetic field lines show?
- the shape of the field -the direction of the field line at a point shows the direction in which a plotting compass would point
What is a solenoid
a long coil of current-carrying wire
What does it mean if the field lines are drawn closer together?
that the field is stronger
True or false: magnetic field lines have a beginning and end
False- they have no beginning or end , they always form a closed loop *the direction is from a north pole to a south pole but they do not begin at north and end at the south
*notice how the field lines continue in the solenoid , similarly magnetic field lines continue inside a bar magnet to close the loop

When is the right hand rule used?
when an electric current is flowing in a straight conductor

What is dot and cross notation
dot and cross notation indicates the direction of the current : a circle with a dot shows the current is coming out of the page and a cross is moving into the page
What does the north-south polarity of a solenoid depend on?
it depends on the direction of the current
Using the right-hand rule :
in this case the curling of your fingers indicates the direction of the current flow around the solenoid and , your thumb will point towards the north pole of the magnetic field of the solenoid
Describe the field inside the solenoid

the field is strong and very uniform - this is demonstrated by the closely spaced parallel lines
What would occur if a magnetic material was placed inside a solenoid?
the magentic field would increase considerably
Sketch the pattern of magnetic field lines around a solenoid
inside the solenoid , the field is strongest and very uniform but outside the coil ,the field is similar to the magnetic field produced by a bar magnet

Sketch the pattern of magnetic field lines around a single coil carrying current

Sketch the pattern of magnetic field lines around a bar magnet

Electromagnets can be switched on and off by having an electric current flowing through them. Explain what happens to the magnetic field of a solenoid when the current stops
the magnetic field is created by moving charges in the wire , so no current means the magnetic field would dissapear
Define Magnetic flux ø
its the product of magnetic flux density ,B, and the area at right angles to the flux : ø =BAcos(theta)
where theta is the angle between the field lines and the normal to the surface
*the unit for magnetic flux is Weber (Wb)
Define magnetic flux density, B
Its a measure of the strength of a magnetic field and its a vector quantity
When will the flux be maximum/minimum?
max when theta = 0º
and zero when theta = 90º
Typical values for a variety of flux densities

Did you know?
Unlike electric charge, which can exist as isolated positive or negative charges , magnetic poles cannot exist as isolated north or south poles - even if you were to slice a magnet into even smaller and smaller pieces you would always have a north and south pole together
What does Fleming’s Left hand rule show?
it shows the direction of the force on a conductor carrying a current in a magnetic field
Force/Motion - thumb
Field - First finger
Current - Second finger
What is 1 tesla equal to?
Wb/ m² (no. of field lines per unit area)
Fleming’s left-hand rule allows us to determine the direction that a current- carrying wire will move when placed in a uniform magnetic field but how do you find the magnitude of the force (which causes the movement) acting on a current -carrying wire?
F= BILsintheta
B- magnetic flux density of the magnets magnetic field
I- current flowing in the wire
L- length of wire within the region of the magnet’s magnetic field
-sine of the angle ,theta, between wire and field lines
When is the force acting on a current carrying wire max?
when the wire and the field lines are at right angles to eachother →theta = 90º
What occurs if there is a relative motion between a conducting rod and a magnetic field?
the electrons in the rod will experience a force which causes them to accumulate on one end of the rod
this induces an electromotive force (e.m.f) across the ends of the rod exactly as connecting a battery to it would
*if the rod was part of a complete circuit then an induced current would flow through it
