Magnetic fields DONE Flashcards
What is meant by a magnetic field?
A region where a force is exerted on a moving charged particle/ current-carrying conductor
F=Bqv. State the condition under which this equation applies.
The magnetic field must be at right angles to the velocity
Explain how ions moving through an electric field can have no overall deflection when a magnetic field of the required strength is applied.
Magnetic force= Electric force
These forces act in opposite directions/ are balanced/ resultant vertical force is zero.
Describe and explain the shape of a charged particle’s path in a magnetic field.
The path is circular
Because magnetic force due to field on particle is perpendicular to plane containing B and v/ perpendicular to direction of motion of particle
Magnetic force is the centripetal force
A charged particle enters a magnetic field and passes through a thin metal foil within the field. Describe how the path of the particle changes after passing through the foil.
Particle has less energy/ momentum/ speed after foil
So radius of curvature decreases after foil
State 2 equations for magnetic force.
F=Bqv
F=BIL
State the unit for magnetic flux density.
Tesla, T
Explain why two parallel wires attract each other if they are carrying current in the same direction.
Current in wire produces a magnetic field
Field is around wire so that it is into the page at the bottom
Each wire is in the field of the other wire
A current-carrying wire in a field experiences a force
Fleming’s left hand rule tells us that wire 1 experiences a force towards wire 2 and wire 2 experiences a force towards wire 1 hence they are attracted to each other
State what is meant by magnetic flux density and whether it is a vector or scalar quantity.
Vector
The force on one metre of wire carrying a current of one amp at right angles to the magnetic field
F=BIL
Where the magnetic field lines of force from two magnets overlap, their effects add to give a single magnetic shape i.e. composite fields. Somewhere between the 2 poles of bar magnets side by side, the 2 magnetic fields will cancel out. State the name for this place and what it shows us about magnetic fields.
Neutral point
Shows us vector nature of magnetic fields
State what is meant by magnetic flux and give the unit.
Magnetic flux is the product of the magnetic flux density and the area perpendicular to it that it passes through
Unit is the Weber, Wb
State what is meant by magnetic flux linkage and give 3 equivalent units.
The magnetic flux passing through a cold of wire with N turns.
Weber, Wb/ Weber turns/ Tm^2
State what is meant by Faraday’s law of electromagnetic induction.
The induced e.m.f. in a circuit is equal/ proportional to the rate of change of magnetic flux linkage
State what is meant by Lenz’s law.
The induced e.m.f. is such as to oppose the charge that caused it.
Use Lenz’s law to explain why a magnetic ball dropped down a conducting copper pipe falls more slowly than a non-magnetic ball.
The falling magnetic ball induces a current in the copper pipe
By Lenz’s law, the induced current creates a magnetic field that opposes the changing field of the falling magnet
Thus the magnet feels a resistive force upwards as it is “repelled” by this magnetic field so falls more slowly
