Current-Carrying Conductor in a Magnetic Field
A current-carrying wire is surrounded by a magnetic field, and when this wire is placed in another magnetic field the two magnetic fields may interact and produce a force on the wire. This is called the motor effect.
A force mat act on current-carrying conductor when placed in magnetic field. The force acts at right angles to both the current direction and the direction of the magnetic field. When the direction of the current is reversed then so is the direction of the force on the wire. Using Fleming’s Left-hand Rule the direction of the force on the wire can be found.
The effect of the force is reversed if:
The current is reversed;
The direction of the magnetic field is reversed
Experiments
A simple way to show the force on a current-carrying conductor.
Apparatus:
stiff copper wire, two steel rods, two magnadur magnets and yoke, low-voltage d.c. power supply, two connecting wires, two crocodile clips, clamps
Procedure:
1) Clamp the two steel rods horizontally, parallel to one another. 2) Bend a length of copper wire as shown to form a ‘swing’, which can hang between the steel rods. 3) Attach the two magnets to their yoke, ensuring that opposite poles are facing each other. Place the magnets around the swing. 4) Connect up the ends of the steel rods to the power supply. The current should be able to flow along one rod, through the swing and back through the other rod. 5) Switch on and observe whether a force acts on the swing.
Force on a Moving Charge on a Magnetic Field
When a beam of positive charges enter the region of magnetic field, the beam is deflected to move in a circular path. This is because the moving charges experience a force perpendicular to its velocity. The direction of the force can be predicted by Fleming’s Lefthand Rule and taking the current to be in the direction of positive charges. When a beam of protons enter a region of magnetic field directed out of the plane paper, the beam is deflected downwards. When a beam of protons is directed into a plane of paper, the beam of protons is deflected upwards
Moving Coil Loudspeaker: the permanent magnet used in a moving coil loudspeaker has a cylindrical pole (S-pole) and a surrounding ring pole (N-pole) to create a strong radial magnetic field in the gap between the poles. When an alternating current passes through the coils, a force is produced which moves the coil forwards and backwards through a short distance. By attaching a paper cone to the coil,. The air molecules in front of the coil and the paper cone are set into motion as the coil and the paper cone move forwards and backwards which creates sound waves in the air.
Two Parallel Current-carrying Wires
When two current carrying wires are placed parallel to each other the magnetic fields will interact and a force will act on each of the wires. When the currents flow in opp. directions, the wires repel and when the flow in mutual directions they attract. The magnetic field pattern of a current carrying wire can be found by applying the right-hand grip rule.
Current-Carrying Rectangle Coil in a Magnetic Field
A current carrying rectangular coil in a magnetic field will experience a turning force.
To increase the turning effect on the coil:
increase the number of coils on the coil;
increase the current;
place a soft iron-core within the magnetic field lines.