N S Magnetic field lines ALWAYS run north to south. The number of magnetic field lines denotes the strength of the magnetic field (B). The more lines the stronger the magnet B = number of field lines or flux per square metre in units called Tesla (T) after Nikoli Tesla

geographic north magnetic north geographic north s N

Professor Hans Christian Oersted 1820 Professor Oersted was demonstrating an experiment for students when he accidentally discovered that a compass needle moved when it was close to a wire connected to a battery.

Oersted noticed that if the current was running in one direction the red part of the needle pointed toward the wire. B I

However if the current flowed in the opposite direction then the red part of the needle pointed way from the wire B I

From this observation a rule was developed Thumb = direction of current. Fingers = direction of mag field lines RIGHT HAND GRIP RULE:

- current outwards current inwards Current is coming out of the page Current going into the page Use thumb and fingers of right hand grip rule to work out direction of field.

THE SOLENOID length l The size of the magnetic field can be increased by the following ways: Increase the number of turns. Place an iron core in the centre. Increase the current. I The field lines of each wire interact to increase the overall strength of the field. Again use thumb and fingers of the right hand grip rule to calculate which way the filed runs. NORTH always has field lines coming out of the solenoid.

Interaction between a magnet and the field due to a current S N S

N S F The interaction of 2 fields. One form the magnet and one from the current carrying wire interact. Where they are going in the same direction they add together in strength. Where they go in opposite directions they cancel out. A force is then applied in the direction of the greatest force. In this case upwards.

FOREFINGER = FIELD FLEMING’S LEFT HAND MOTOR RULE To determine the direction of force the following rule needs to apply: THUMB = MOTION FOREFINGER = FIELD SECOND FINGER = CURRENT FLEMING’S LEFT HAND MOTOR RULE

FOREFINGER = FIELD FLEMING’S LEFT HAND MOTOR RULE THUMB = MOTION SECOND FINGER = CURRENT

N S I B F F = B I L Where L = length of conductor in the field

MOVING COIL METER This is seen in any analogue meter: Galvanometer Ammeter Voltmeter S N PERMANENT MAGNET RADIAL SOFT IRON POLE PIECES COIL HAIR SPRINGS CONTROL MOVEMENT AND ALLOW CURRENT TO ENTER AND LEAVE THE COIL SOFT IRON CYLINDER

S N + + This shows the rotation of the coil and hence the needle as the current flows through the wires of the solenoid and produces a magnetic field which interacts with the static magnet. The more current the more rotation as the greater the magnetic field interaction.

DC MOTOR A B D C C A B S N D N S I I brushes Split ring commutator EVERY TIME THE COIL PASSES THROUGH THE VERTICAL POSITION, THE COMMUTATOR REVERSES THE CURENT IN THE COIL, IN ORDER TO SUSTAIN THE ROTATION

Solenoid on paper cone is forced to vibrate - left hand rule LOUDSPEAKER N S magnet magnet S N Solenoid on paper cone is forced to vibrate - left hand rule coil AC signal

THE PARTICLE MUST MOVE ALONG AN ARC OF A CIRCLE Charged particle moving through a magnetic field THE FORCE IS ALWAYS PERPENDICULAR TO THE MOTION F F THE PARTICLE MUST MOVE ALONG AN ARC OF A CIRCLE + + I

If the magnetic field is of a large enough area then the effect on the charged particle would be to produce a circular motion. If not then the particles trajectory will be diverted. What determines how much is how long it remains in the magnetic field area. x x x x x x x x x x x x B inwards +

Do Exercises from Pages: 177 - 190 Rutter