Magnetic Fields Flashcards
(17 cards)
What happens to a wire with current?
When current flows through a wire or any long straight conductor, a magnetic field is induced round the wire. The direction of the field can be worked out using right hand grip rule.
What is Flemings left hand rule
First Finger = direction of the uniform magnetic Field
seCond finger = direction of the conventional Current (positive to negative)
The thuMb = direction of the force (direction of Motion)
What is a Tesla?
Magnetic flux density is measured in Teslas = one newton per amp per metre
What is magnetic flux density?
The force on one metre of wire carrying a current of one amp at right angles to the magnetic field
What will happen when a charged particle moves through a magnetic field?
It experiences a force F=BIL=BQV (V is velocity)
Why do charged particles In magnetic fields follow circular paths?
When magnetic field is perpendicular to the velocity
How does a particle accelerator work?
Good example is a cyclotron that works by have two semicircular electrodes with a uniform magnetic field applied perpendicular to the plane and an alternating p.d applied.
Applied p.d accelerates charged particle each time it crosses gap.
As speed increases, its radius gradually increases each time it crosses gap between electrodes.
Since pd is alternating it accelerates particle every time.
Since frequency doesn’t depend on radius, it will always spend the same amount of time in each electrode
What is magnetic flux and what is it measured in ?
The total flux passing an area.
Measured in Webers (Wb)
Explain electromagnetic induction
Am e.m.f (potential difference but don’t call it p.d) is induced by a conductor and a magnet when the conductor cuts the magnetic flux (doesn’t matter which one moves) . This can be either negative or positive depending on direction of motion.
How can electromagnetic induction induce current?
If the coil is a complete circuit then an induced current will flow through it.
What is faradays law ?
Induced e.m.f is directly proportional to the rate of change of flux linkage (this can also be used to give the magnitude of e.m.f )
What is Lenz’s law ?
The induce emf is always in such a direction as to oppose the change that caused it (agrees with the conservation of energy)
What is alternating current how can it be measured?
Alternatin current in one that changes direction with time.
Using an oscilloscope, alternating current will display a sinusoidal wave and direct current will give a horizontal line
How can you measure alternating voltage with an oscilloscope?
Vary the y axis scale using the y gain control dial to vary voltage per division.
How can you analyse oscilloscopes?
You can fine the time time period and use it to work out the frequency
How do you work out the average power?
Root mean square for both voltage and current and multiply P=IV
How does a charged particle travel in a semi circular path in a dee?
Due to F=BQV, force due to the magnetic field is constant always at 90 degrees to direction of travel causing centripetal force.
