unit 7 physics

drawing magnetic field

• place plotting compass near magnet on a piece of paper

• mark direction the compass needle point

• move the plotting compass to many different positions on the paper

• join the lines

induced potential

• electrical conductors move relative to a magnetic field, or if there’s a change in the magnetic fried around a conductor, a pd is induced across th ends of the conduct, if part of a complete circuit, a current is induced

increasing electromagnet strength

• decrease length of coil, same number of turns, densely packed coils are strongest

• add iron core, soft magnetic material, becomes an induced magnet

how do loudspeakers work

• current creates a magnetic field around the coil

• which interacts with the permanent magnetic field

• producing a resultant force, causing the coil/cone to move

• when direction of current reverses, the direction of forces reverse

• cone vibrates in and out, producing sound waves

loudspeaker

• converts vibrations in current in electrical circuits to the pressure variations in sound waves

increase size of an alternator

• increasing rotating speed of the coil, increases both size and freqncues, cuts more fields per second

how do alternators work

• coil spins, moves through magnetic field, so a pd is induced, complete circuit, current induced

• each side always connected to the same ring, so every half tun, pd reverses direction, so current changes direction

alternator

• coil of wire rotating in a magnetic field,

• coil connected to 2 metal rings, which all the current to pass out of the coil

how do transformers work

• primary voltage drives ac through primary coil

• produces an alternating magnetic field which changes as the current changes

• induces an alternating magnetic field in the iron core, as induced magnet

• this magnetic field induces pd across secondary coil, and hence current as its a complete circuit

transformer

• a device that Inca change the pd of an alternate current by the induction of a pd when a wire experience a change in the magnetic field

magnetically soft

nickel and iron

magnetically hard

steel

induced current, magnets repel

• inser N pole into the coil, the end of the coil become NP

• this repels the magnet so harder to push in

• when pull N pole out, comes S pole

• this attracts the magnet

  • so induced current makes it harder to move the magnet, means we’re doing work

  • as transferring energy from the movement of the magnet into the movement of the current

a compass

• small bar magnet that points in the direction of earth’s magnetic field

microphones, work

• sound waves cause diaphragm to vibrate

• cause coil to vibrate

• coil/wire moves through the magnetic fiekd

• so a pd is induced across the ends of the coil/wire

electric motor

• coil of wire, carrying a current, in placed in magnetic field

• forces on two sides perpendicular to the field experiences force in opposite idrectons

• cause a rotational effect

• split ring commuters, swap contacts every half turn, keep the motor rotating the same direction

  • swapping the polarity of the dc supply, revers current

  • swapping magnetic poles over, reverse field

motor effect

• when a conductor carrying a current is placed in a magnetic field, th magnet producing the field and the conductor exert a force on each other

increase speed of rotations

• increase current

• add more turns to the coil

• increasing magnetic flux density, stronger magnet

magnetic field induced potential

• generates a magnetic field that opposes the original change, either the movement of the conductor or change in the magnetic field