magnetism and electromagnetism Flashcards
4 ways to increase strength of electromagnet:
-plus no. of coils (keeping length of coil same
-less length of coil (keeping no. of coils same)
(stronger when coils densely packed)
-increase current that flows through coil
-put iron core inside coil (it is a soft magnetic material, becomes an induced magnet in presence of field
3 ways to + size of induced p.d.
-plus no. of coils
-move wire or magnet faster
-use stronger magnets
Explain how an electromagnetic induction (generator effect) is used in dynamos
-coil of wire is turned inside mag field
-induces a (mag field and) current in the coil of wire
-commutator switches connections every half-turn
-causes current to be in one direction (d.c.)
how do loudspeakers work:
take elec signals, convert into vibrations, which then generate sound waves
how do loudspeakers work:
take elec signals, convert into vibrations, which then generate sound waves
how do microphones work:
detect vibrations caused by sound waves and use generator effect to turn them into elec signals
explain how a loudspeaker converts electrical signals into sound waves:
-coil of wire carrying an alternating current is wrapped around a pole of a permanent magnet which is surrounded by the other pole, attached to a paper cone
-when current flows through wire, causes force which moves cone in one direction
-when current reverses, force reversed, cone moves in opp direction
-makes come vibrate, vibrates the air around it to create sound wave of same freq as the a.c
explain how a dynamo generates current:
-coil made to rotate in mag f
-induces a p.d. across coil, causes current to flow through it
-split ring comm used to swap the connection each half turn to keep current flow in same direction
state the generator effect:
-the induction of a p.d in a wire which is moving relative to a mag f or experiencing change in mag f
what do step up transformers do?
-increase the p/d
bcs less turns on primary coil than sec coil
what do step down transformers do?
-decrease p/d
bcs less turns on sec coil than primary coil
how does a moving coil loudspeaker prod. a sound wave
-current prod. an m. field around the coil
-which interacts with the permanent magnet m. field
-resultant force causes the coil to move
-alternating current means alternating forces (direction reverses) - prods a sound wave
what does changing the frequency of AC supply in a motor do
changes the frequency that the cone vibrates
a high frequency will prod a …. pitch sound, a lower frequency will prod a …. pitch sound
-higher
-lower
what does increasing size of current do in a loudspeaker
-increases the amplitude of the vibration
-this increases vol.
what type of current do dynamos prod
bcs of split ring commutator, it prods. a direct current
what type of current do alternators prod
bcs of the slip ring and brushes, they prod an alternating current
why are iron cores used in elecmags
-Having an iron core in the center increases its strength as it is easier for magnetic field lines to pass through than air
Factors that affect the strength
o Size of current
o Length
o Cross sectional area
o Number of turns (coils)
o Using a soft iron core
what does a commutator do
allow the current to pass out of the coil
what is generator effect
-induction of a p.d. (and current if circuit is complete) in a wire which is moving in a magnetic field, or experiencing a change in magnetic field
Explain how Fleming’s left hand rule can be used to predict the direction in which the
copper rod will move
- hold thumb first finger and second finger (of left hand) at right angles to each other
- second finger represents the current
- first finger represents the field
- thumb points in the direction of the force / thrust / acceleration
what is induced current
when a coil/conductor is moved perpendicular to a magnetic field, there will be an induced voltage in the conductor/coil
-if conductor is part of a closed circuit then induced voltage will cause induced current in wire
Explain how electrical signals in the transmitter produce a signal in the receiver.
[3 marks]
-electrical current in the transmitter producing radio waves
-which are absorbed by the receiver inducing electrical current in the receiver
-at the same frequency
