P.50 Magnetic effect of a current

P.50 North pole and South Pole

P.50 Like poles repel

P.50 Unlike poles attract

P.50

NS Compass needle shows the direction of magnetic field lines P.50

Magnetic field Magnetic field lines Magnitude & direction of magnetic force acting on a north pole Magnetic field line starts at north pole No intersection of magnetic field lines Magnetic field line ends at south pole N P.50

Neutral point Magnetic forces are balanced N N P.50

I = 0 A P.51

Current flows Magnet affects compasses Magnetic field P.51

Right-hand grip rule Thumb Fingers Direction of current Direction of magnetic field lines P.51

Current flows out of paper P.51

Current flows into paper P.51

Electric current Magnetic field P.51

Right-hand solenoid rule Thumb Fingers Direction of current Direction of magnetic field lines P.51

Iron filings show the magnetic field pattern P.51

N S Solenoid Produces the same magnetic field pattern as a bar magnet A long coil with many turns P.51

P.52 X : South pole, Y : North pole (a) Current in wire will produce Magnetic field to affect the compass (b) To stop the light from the bulb by a black box X : iron, Y : Magnet, Z : Al

Each part of the wire produces the magnetic field lines in the same direction in the central part of the circle P.53

N S

Methods to strengthen B-field P.53 Increase current Winding more turns per unit length Insert a soft iron bar inside the solenoid

P.54 Follow Earth’s magnetic field

P.54

P.55 To align the Earth’s magnetic field N Earth North pole is produced to attract South pole of magnet N S Earth S

P.55

Cancellation Out of paper Into paper

P.55 I I

Electromagnet P.56

Solenoid with current Electromagnet can be strengthened Larger current Increase number of turns of coil Use soft iron core Electromagnet Direction of field lines can be reversed or alternate On or off any time P.56

Horse-shoe magnet P.56

Ferromagnetic material Substance attracted by magnet

Electromagnetic Lifter Pick up heavy iron objects P.56

Maglev Giant electromagnet repels magnetism induced on the track P.56

Switch is on Current flows Electromagnet attract metal plate Hammer strikes on the bell Circuit is broken Hammer goes back P.57

Compression Diaphragm inwards Resistance decreases Diaphragm inwards Current increases P.57

P.58

t I Diode allows the current flowing in one direction only When the current is larger than a value, the electromagnet can attract the iron arm f = 50 Hz P.58

N S N S S N Reed switch Reeds touch one another when magnetised P.58

Reed relay Bar magnet is replaced by an electromagnet P.58

Switch is closed Current flows through the solenoid Main circuit is completed P.58

A small current flows A large current flows Relay A small current is used to control a large current P.58

Current flows Attract the contact P.58

Reed switch is on when the door is opened P.58

Reed switch is off when the door is closed Neutral point P.58

P.59 Induced North pole is induced. N S M : South pole N Iron bar is attracted downwards

P.59 Iron bar returns to the original position

P.59 Induced South pole is induced. S N M : North pole S Iron bar is attracted downwards 2 dots within 1 cycle 100 dots in 1 second

P.59 The soft iron bar is magnetized to attract the arm and hit the bell The arm will be attracted permanently.

P.60 Increase no. of turns per unit length To avoid the sparks when contacts touch each other Current flows through the circuit, magnetic field is produced and induced poles are produced on the contacts. They attract each other and conduct electricity. The soft iron is magnetized to attract the steel ball for a while Increase e.m.f. of cell

P.60 7a) Attract downwards Increase no. of turns per unit length Weaker spring to have greater extensions under same amount of force 7c) Same current -> Greater attractive force 7b) No.

P.61 Yes Reduce R ->increase I Yes No

P.61 NS