1. A thick copper wire XY is connected to anelectric circuit.2.A small compass needle is placedunderneath3.Note the position of the needle.4. Current is passed through thecircuit by inserting the key inthe plug5. The needle is observed6. The compass needle gets deflected.7. WHY SHOULD IT GET DEFLECTED?
1. A mag. Needle gets deflected inpresence of a magnet, due to theinfluence of mag. Field of bar magnet.3. Therefore the deflection of mag.needle kept under the currentcarrying wire is due to the mag. fieldproduced by the wire.3. Thus electricity and magnetism arelinked to each other.
A compass needle is a small bar Magnet.A freely pivoted magnetic needle always pointapproximately towards north- south direction.(DIRECTIONAL PROPERTY)The end pointing towards north is called northseeking or north pole.The end pointing towards south is called southseeking or south pole.Recapitulation - Magnetism
OTHER PROPERTIES• Unlike poles Attract• and like poles repel• POLES EXIST IN PAIRS• (MONO POLES DOES NOT EXIST)
Activity 11 A sheet of white paper is fixed on adrawing board2 A bar magnet is kept in the centre andiron filings are uniformly sprinkledaround the bar magnet3 The board is tapped gently.4 The iron filings arrange themselves ina pattern as shown.5 This represents the magnetic fieldaround the magnet.6 The iron filings arrange them selves dueto the force exerted by the bar magnet.7 The field can be plotted using acompass needle also.
The region surrounding a magnet , in which the force ofmagnet can be detected is said to have a magnetic field.Magnetic field is a quantity that has both magnitude anddirection.The curved lines along which the iron filings alignthemselves or the path along which the freely pivotedmagnetic needle moves is called the field lines ormagnetic lines of force.The direction of the field is taken to be the direction inwhich a north pole of the compass needle moves insideit.
Characteristics of magnetic field1. Strength of magnetic field is a quantity that can beexpressed both in magnitude and direction.2. The relative strength of a magnetic field is shown by thedegree of closeness of magnetic field lines; (i.e. greaterthe number of magnetic field lines in a unit space, more isthe strength of magnetic field)3. The strength of magnetic field at a given point dependsupon its distance of from the poles of a bar magnet. (i.e.more the distance, less is the strength of magnetic field.)
Characteristics of magnetic field line.• 1. A magnetic field line can be defined as the path along which afree north pole will move in a magnetic field.• 2. Magnetic field lines are closed curves.• 3. Magnetic field lines appear to start from N-pole and appear toend at the south pole.(within the magnet , they run from S- pole to N- north pole)4. Magnetic field lines repel each other.5. No two magnetic lines cut each other. ( If they intersect , acompass needle placed at the intersection has to point two differentdirections at the same time which is impossible.)
Right-hand Thumb Rule• When you wrap yourright hand around thestraight conductorsuch that the thumbpoints in the directionof the current, thefingers will wraparound the conductorin the direction of thefield lines of themagnetic field..
Magnetic field due to current through astraight conductor. The current through a wireproduces a magnetic field. The shape of the magneticfield lines for a straightconductor is concentriccircles. These concentric circlesbecome larger as we moveaway from the wire.
Magnetic field due to current in a straightlong conductor1. Take a thick copper wire andpass it through a horizontal cardboard as shown.2. Pass a strong current through thewire.3. Sprinkle iron filings on thecardboard around the wire.4. Tap the cardboard gently. Youwould see a pattern as shownhere.5. You may plot the field lines witha compass needle also.
• 1. The magnetic field lines are in the form ofconcentric circles near the conductor2.Away from the conductor the field lines tendto be elliptical due to the combined effect ofearth magnet and mag. Field due to theconductor.3.The direction of magnetic field lines reverseswith the reversal of the direction of current inthe conductor.4.Increasing the strength of the current in theconductor results in increase in mag. Field lines .
that is intensity of magnetic field increaseswith the increase in strength of the current.(No of magnetic field lines around theconductor increases)5. The magnetic field at a point decreases withthe increase in distance from the conductor.
Review QuestionA current through a horizontal power line flows in eastto west direction. What is the direction of magneticfield at a point directly below it and at a point directlyabove it?EastNorth southWestAnswer:Below : North – SouthAbove : South to North
Magnetic field due to current in a circularloopProperties of magnetic field lines1. The magnetic field lines are nearcircular at the points where thecurrent enters or leaves the card board2. Within the space enclosed by the coil,the field lines are in same direction.3. Near the centre of the coil, themagnetic lines are almost parallel toeach other. Thus mag. Field near thecentre of the coil may be considereduniform.4. At the centre of the coil the plane ofmagnetic field lines is at right angle tothe plane of the coil.5. If there is a circular coil having n turns,the field produced is n times as largeas that produced by a single turn ,asthe current in each turn has the samedirection and the field due to each turnadd up.
Solenoido A coil of many circularturns of insulatedcopper wire wrappedclosely in the shape of acylinder is called asolenoid.o A solenoid produces amagnetic field whenelectric current ispassed through it.o The pattern of themagnetic field linesaround a current-carryingsolenoid is similar to thatof a bar magnet.o One end of the solenoidis like a magnetic northpole while the other islike the south pole
The strong magnetic field produced inside a solenoid can be used tomagnetize a piece of magnetic material like soft iron when placed inside acoil. The magnet so formed is called an electromagnet.
Force on current carrying conductorin a magnetic field1. A aluminium rod AB is suspendedbetween the pole pieces of a horseshoe magnet as shown.3. A current is allowed to flowthrough the conductor AB in thedirection from B to A4. The conductor id found to getdeflected to the left as shown bythe arrow5. When the poles of the magnet isinterchanged and when the currentis still from B to A, the force on theconductor is found to be on theright as shown.
5.If the current is from A to B( Directionis reversed) without reversing the polepieces of the magnet. The deflection ofthe conductor(force) is to the left asshown.6. If the current is from A to B( Directionis reversed) reversing the pole pieces ofthe magnet.The deflection of theconductor(force) is to theright as shown.
Force on a current-carrying conductor in amagnetic field• An electric current flowing through a conductorproduces a magnetic field. The field so producedexerts a force on a magnet placed in the vicinityof the conductor.• The magnet also exerts an equal and oppositeforce on the conductor.• The magnitude of this force is highest when thedirection of current is at right angles to thedirection of the magnetic field.
• To Sum up• The direction of force is reversed when the directionof current through the conductor is reversed.• The direction of force is also reversed byinterchanging the two poles of the magnet.
Fleming’s left-hand rule• The directions of the current, force, and magneticfield can be illustrated through a simple rule calledFleming’s left-hand rule, if the direction of current isat right angles to the direction of the magnetic field.• According to this rule, stretch the thumb, forefinger,and middle finger of your left hand such that theyare mutually perpendicular.• The first finger points in the direction of themagnetic field and the second finger in the directionof the current, then the thumb will point in thedirection of motion or the force acting on theconductor.