Magnets Flashcards
When a magnetic field is perpendicular to a current-carrying wire, does the wire feel a force
Yes, the magnitude of the force is = BIl
What is magnetic flux density (B)
Flux density measured in Tesla (T) is the flux per metre²
A charged particle moving through a field feels a force when it is traveling along the field lines or perpendicular to them
Perpendicular to the field
Is the force applied to the particles applied perpendicular to the particles motion or in one direction
Perpendicular to its motion, causing it to
move in a circular motion
What fields do cyclotrons use
An electric field and a magnetic field
How does a Cyclotron work and what’s the electric and magnetic fields purpose in a cyclotron
- A cyclotron is made up of 2 semicircular electrodes called “Dees” with a magnetic field applied perpendicular to the Dees and an alternating pd applied between the Dees.
- Each Dee is a metal electrodes with opposite charges, this creates an electric field in the gap between the two Dees.
- This is what accelerates the particles.
- The magnetic field causes the particles to move in a circular motion, which allows it to
gain speed whilst minimising space. - As they speed up the radius of their motion increases, until it breaks free tangential to one of the Dees.
What is magnetic flux
The product of the magnetic flux density and the perpendicular area the magnetic field passes through
What is flux linkage
The number of turns cutting the flux at one time
What is Faraday’s Law
The induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage
What is Lenz’s Law
The direction of the induced e.m.f. is such as to oppose the change that induces it
What happens when you move a straight conductor through a magnetic field
The electrons experience a force pushing
them to one end of the conductor creating an emf across the conductor.
The rod obeys Faraday’s law, so it changes flux as it moves through the field hence an EMF is induced
How does a transformer work
A primary coil wrapped around an iron core with an alternating p.d. creates an alternating magnetic field, this magnetic field induces an EMF in a secondary coil also wrapped around the core. This creates a current in the secondary coil
What kind of current is produced by a transformer and why
An alternating current.
An EMF is induced by a changing magnetic field, hence the EMF induced is alternating producing an alternating current
Why are transformers used
By changing the number of coils, the
transformers can be used to increase the voltage and reduce current when transporting power, with minimal energy loses. The voltage is then dropped again locally to ensure safe usage in households
In a step-up transformer, does the secondary coil or primary coil have more coils
The secondary coil.
Step-up transformers increase the voltage, hence more coils need to be in the secondary coil for a larger p.d
What is an eddy current
As the primary coils magnetic field induces emf in the secondary coil, it also induces emf and hence mini currents within the iron core.
Why are eddy currents a problem
By Lenz’s law the emf created and its field opposes that of the primary coil. This causes energy loss via resistive heating of the iron core by the eddy currents, which reduces efficiency
How can you reduce eddy current losses
Use a laminated iron core.
Thin sheets of iron with an electrical insulator in between, which reduces the eddy currents circuit
