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p4 (transformers (change size of the pd of an ac, two coils, primary and…
p4
transformers
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two coils, primary and secondary joined with an iron core
when an alternating pd is applied across the primary coil, produces an alternating mag field
iron is a mag material, core becomes magnetised, because coil is producing an alternating mag field, magnetisation in the core also alternates
changing mag field induces a pd in the secondary coil, power of a primary coil is given by power = pd x current, nearly 100% efficient so power in primary = power in secondary
is the secondary coil has more turns, pd increases and current decreases or vice versa
step down = steps voltage down, more turns on primary coil
step up = steps voltage up, more turns on secondary coil
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motors
in a dc motor, current carrying coil is between two opposite poles of a magnet
current flows in different directions on each side of the coil, each side of coil perp to mag field, each side side feels forces in opposite directions
coil on a spindle, rotates, split ring commutator swaps the contacts every half turn to keep motor rotating in same direction
direction of the motor can be reversed, swap polarity of dc supply (reverse current) or swap magnetic poles (reverses field)
to speed up increase current, add more turns to coil or increase mag flux density
loudspeakers
force between current carrying coil or wire and mag field can make things move back and forth like in loudspeakers
contains coil of wire surrounded by one magnet, another magnet inside the coil
ac electrical signals fed to coil of wire, wrapped around base of a cone
interaction between mag field and current in coil forces coil to move in one direction, as it's ac, current changes direction, forces coil back in other direction, continues to alternate coil moves back and forth
movements make cone vibrate, creates pressure vibrations in air, ie sound
generators
opposite of motors, use relative motion of a conductor and mag field to induce a pd and a current
if direction of rotation reversed, direction of induced pd/current reverses
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alternators
rotate a magnet in a coil of wire, as magnet spins, alternating pd is induced across the ends of the coil
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produces an ac if the coil is part of a complete circuit, can generate ac by rotating a coil in a magnetic field
slip rings at the ends of the coil remain in contact with the brushes connected to the rest of the circuit
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dynamos
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output pd and current change direction with every half rotation of the coil, producing ac, coil part of a complete circuit
split ring commutator swaps the connection every half turn to keep current flowing in the same direction so it changes ac to dc
microphones
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sound waves cause the diaphragm to move back and forth when hit by them, as the diaphragm moves the coil of wire moves, induces pd across the ends of the coil of wire
coil part of a circuit, induced pd means variations in current in the electrical circuit