Use of magnetisum Flashcards
(20 cards)
What is an electomagnet?
An electromagnet is a magnet whose magnetic field is created by an electric current through a coil of wire, often wrapped around a solenoid with an added iron core -Adding the iron core increases the strength of magnetic field
What is the motor effect?
When a force is exerted between a magnetic field and a current-carrying conductor placed in that field.
When using Fleming’s left hand rule
what does the index finger represent?
Points in the direction of the magnetic field
When using Fleming’s left hand rule
what does the middle finger represent?
Points in the direction of current flow in the conductor
When using Fleming’s left hand rule
what does the thumb represent?
points in the direction of the
force produced, and therefore the motion
produced by the force.
What factors affect the size of the force on a
current-carrying wire in a magnetic field?
-The magnitude of the current flowing through the conductor. -The strength of magnetic field that the conductor is placed
If the direction of current in a
current-carrying wire placed in a uniform
magnetic field is reversed, what happens
to the force?
The direction of the force is reversed.
If the strength of the current in a current-carrying
wire placed in a uniform magnetic field is increased,
what happens to the force?
The strength of the force is increased.
What criteria must be met for the equation linking
force, magnetic flux density, current and length to
hold?
The conductor must be at right-angles to
the magnetic field it is placed in.
What is the unit used for magnetic flux
density?
Tesla, T
What equation is used to calculate the force that a
current carrying wire experiences in a field?
Force (N) = Magnetic Flux Density (T) x
Current (A) x Length (m)
F = BIL
How does an electric motor work?
- A coil of wire, carrying a current, is placed
in a magnetic field. - The forces on the two sides perpendicular
to the field experience forces in opposite
directions. - This causes a rotational effect.
How do loudspeakers make use of the
motor effect?
The motor effect is used to convert
variations in the current of an electrical
circuit into the pressure variations which
produce audible sound.
Explain how a loudspeaker works.
- A cone with a wire wrapped around it is connected to an
a.c power supply and is placed in a permanent
magnetic field. - When current flows through the wire, it creates a
second magnetic field, which interacts with the
permanent field. - This produces a force which causes the cone to vibrate
What happens when an electrical
conductor moves relative to a magnetic
field?
A potential difference is induced across
the ends of the conductor.
What happens to an electrical conductor
when there is a change to the magnetic
field that it is placed in?
A potential difference is induced across
the ends of the conductor
What condition must be met for an induced potential difference to cause a current to flow?
The conductor must form a closed loop
or be part of a complete circuit.
What can be said about the direction of
the magnetic field produced by an
induced current?
- The direction of the field is such that it
opposes the change that induced the
current. - This change is either the movement of
the conductor or a change to the field.
If there is a change in the magnetic field
around a conductor, explain what
changes occur in the conductor.
- A potential difference is induced across its ends.
- This drives a current.
- The direction of the induced current is such that it
creates a magnetic field that opposes the change
in the existing field.
Why is iron used as the core for a
transformer?
It is easily magnetised.
