3.7.5 - Magnetic fields Flashcards
What is the function of a transformer core?
it provides greater linkage from primary to secondary coil compared to an air coil
Why is 33kV not used for long-distance transmission?
A lower voltage will mean the power is transmitted at high current. So energy is lost in the cable due to heating
Why is 400kV not used for long-distance transmission?
Too high a voltage will cause major insulation difficulties
Which way do electrons flow?
From the negative terminal to the positive one
Which way does conventional current flow?
From positive to negative
Which way do megantic field lines go?
From the North Pole to the South Pole
Describe the sturcture of a cyclotron
Two hollow semicircular electrodes with an alternating potential difference applied between them. A magnetic field is also applied perpendicular to the plane of the electrodes
How does a cyclotron work?
Dees placed in a vacuum chamber with magnetic field within them and electric field between them. A particle moves in a circle due to Fleming’s left-hand rule where the force is always perpendicular to velocity. After it reaches the gap, the other dee has the particle’s opposite charge so it accelerates to that one. This continues until the particle moves at the required speed for the experiment and leaves the cyclotron
What is a mass spectrometer used for?
To analyse the types of atom in a sample
What happens to the path of heavier atoms in mass spectrometers?
They move in bigger circles (radius) than lighter ones
What happens when pair production happens in a magnetic field?
The electron moves in a circle one direction and the positron moves in a circle in the other direction
Why is a magnet strongest at its poles?
Their is a higher concentration of field lines and so there is a stronger magnetic field
When is flux linkage a maximum?
When the magnetic field lines are perpendicular to the plane of the area (angle between normal to field and area plane =0)
When is flux linkage minimum?
When the plane of the area is parallel to the field lines (angle between normal to field and area plane =90)
What are two ways emf can be induced in a wire?
Moving the wire through a magnetic field
Move a magnet through a coil of the wire
Why does electromagnetic induction happen?
The wire is cutting through magnetic field lines (and vice versa)
How do you find which is the North Pole on a solenoid?
Using the right hand grip rule: have your fingers follow the direction of the current and your thumb points out of the North Pole
How does a solenoid produce a magnetic field?
When a current flows through it
How do p.d. and/or current act in d.c. circuit?
They’re constant
How do current and/or voltage act when the battery of a d.c. supply is reversed?
They are constant in the negative direction
What does the second finger in Fleming’s left-hand rule represent?
The direction of motion of the positive charge
Describe one cycle of voltage and/or current act in an a.c. supply.
They start at zero, reach a positive maximum, fall back to zero, reach a negative maximum, and return to zero
How do you measure the peak value of p.d./ current?
Measure the amplitude
How do you measure the peak-to-peak value of p.d./ current?
Measure distance from positive maximum to negative maximum
