Magnetic Fields Flashcards
(39 cards)
Magnetic Field?
A region in which a force acts on a magnetic or magnetically susceptible materials. They are represented by field lines otherwise flux lines and go from north to the south pole of the magnet. The closer the lines are the stronger the field is
Right Hand Rule?
The orientation of the thumb indicates the direction of the current and the direction in which your fingers curl round indicate the direction of the magnetic field
Soleonoid?
An electromagnet consisting of multiple coils of wire
Solenoid compared to coil field lines?
A solenoid has a narrower set of central field lines but the field lines which connects the wire for the coil is much more circular than the solenoid which is also circular but much more stretched
Resultant Fields?
When fields interact they combine. The closer the field lines the stronger the force and dense lines result in a magnetic force being produced. The size of this force depends on the component of the magnetic field that’s perpendicular to the current
Fleming’s Left Hand Rule?
Thumb orientation identifies the direction of the force, the first finger identifies the direction of the field from north to south, the second finger identifies the current going from positive to negative
Alternating Currents on magnetic fields?
Passing an alternating current through a magnetic field results in a wire vibrating. Since the direction of force is perpendicular to the current the constant reversal of current direction means there’s an interchange of upwards and downwards force which results in the wire vibrating
Magnetic Flux Density?
The force on one meter of wire carrying a current of one amp at right angles to the magnetic field. The force on a current carrying wire at right angles is proportional to the magnetic flux density
Tesla?
One tesla is equal to 1 newton per amp per meter
Magnetic Flux Density Formula?
F=BILsinx where “x” is the angle of orientation of the current carrying wire in the magnetic field. Maximum force occurs when sinx=1 at 90 degrees otherwise when current carrying wire is perpendicular to the field
Investigating Force on a wire experimentally?
Have a wire that passes through two magnets connected to a circuit with an ammeter, power supply and variable resistor by crocodile clips. Secure the mass above a balance. At different settings on the variable resistor, record the current and mass reading. The mass changes from the force on the balance increasing at higher currents. Then plot a force against current graph to show the results
Investigating Magnetic Flux experimentally?
This can be done by testing different strength magnets or using different lengths of wire or changing the current through altering the setting of a variable resistor
Path of charged particles in magnetic fields?
Use the version of Fleming’s left hand rule where: Thumb indicates direction of force, use the first finger to identify the direction of magnetic field from North to South, then use the second finger as the direction of a positive charge in the field
Charged particles entering perpendicular to a magnetic field?
A charged particle perpendicular to a magnetic field will experience circular motion. The faster or heavier the particle the increased the curvature in the radius is. The stronger the magnitude of charge or the stronger the magnetic field the less curvature the radius has. These effects are based on f = mv^2/r and F=BQv being made equal to each other
Frequency of rotation proof?
Equations of Circular motion:
f = v / 2πr
Making F=mv^2/r and F=BQV equal and re-arranging to make “r” the subject:
r = mv/BQ
Substituting “r” into equation of circular motion:
f = BQ/2πm
Frequency of rotation?
Frequency of rotation is the number of rotations a charged particle completes per second as a result of entering a magnetic field perpendicular. It is affected by only magnetic flux density, mass and charge. Increasing velocity only increases the radius, it still takes the same time to complete
Cyclotrons?
Made up of two semi-circular electrodes with a uniform magnetic field perpendicular to the plane of the electrodes. Charged particles are produced and fired into one of the electrodes. An applied potential difference accelerates the particle across the gap between the electrodes. This gives the particles a higher velocity so they can complete a path with a larger radius. Each time this repeats its the same potential difference and it does so until the particles spiral out at high energy
Total Magnetic Flux?
Has the equation Φ=BA and is the number of field lines passing through an area perpendicular to a magnetic field
Electromagnetic Induction?
If there is relative motion between a conducting rod and magnetic field the free electrons in the rod move relative to the magnetic field. This motion means they experience a force and since they are all electrons and have the same charge which means the force moves them all to the same place at one end of the rod. This accumulation of electrons makes one end positive and the other negative. This charge separation creates an electric field which creates a potential difference otherwise an induced EMF
Induced EMF with a conductor and magnet?
An EMF is induced by a conductor and a magnet when the conductor cuts the magnetic field. The conductor can move and the magnetic field stays the same or the other way round, no matter which way an EMF is produced. This is because the magnetic flux that passes through the coil changes and the coil is the complete circuit which the induced current flows through
Flux Linkage?
The product of the magnetic flux passing through the coil and the number of turns on the coil cutting the flux. Flux linkage determines the size of the induced EMF when a coil is moved through a magnetic field
Rate of change of Flux Linkage?
A change in flux linkage of one Weber per second will induce an EMF of 1 volt in the loop of wire. This rate of change in flux linkage identifies how strong the EMF will be in volts
The angle of the coil?
Draw a line perpendicular to the coil of wire, then on that line draw a line perpendicular that meets one of the normal lines of the uniform magnetic field. The value of theta is the cosine angle produced.
Investigating Flux Linkage Experimentally?
Have a stretched spring to act as a solenoid when connected to an alternating power supply. The alternating current ensures the magnetic field through the solenoid is constantly changing, this allows for an EMF to be induced. The search coil should have a known area and number of turns and the oscilloscope should be set up to show the amplitude of EMF which means the time base is off. Place a search coil halfway in the spring and angle it at 0 degrees. In intervals change the angle, as it gets closer to 90 degrees the induced EMF should decrease to 0 V from initially being at a maximum at 0 degrees
