Topic 7 - Magnetism and electromagnetism

Question 1

what is a magnetic field

Answer 1

a region where other magnets or magnetic materials experience a force

Question 2

explain how an electric motor works

Answer 2

magnetic forces act on two side arms of a coil of wire that carrying a current.
because the coil is on a spindle and the forces act one up one down , it rotates /

Question 3

how does an electric DC motor keep on rotating in the same direction

Answer 3

split ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction.

Question 4

how can we reverse the direction of a motor

Answer 4

swapping the polarity of the dc supply(reversing the current)
swapping the magnetic poles over(reversing the field)

Question 5

what is fleming s left hand rule and what is it used for

Answer 5

used to work out which way the coil in a motor will turn

first finger - field
second finger - current
thumb - motion

Question 8

explain how a loudspeaker works

Answer 8

an alternating current is sent through a coil of wire attached to the base of a paper cone.
the coil surrounds one pole of a permanent magnet and is surrounded by the other pole. so the current causes a force on the coil (which causes the cone to move)
when the current reverses, the force acts in the opposite direction , which causes the cone to move in the opposite direction too.
so variations in the current make the cone vibrate , which makes the air around the cone vibrate and creates the variations in pressure that cause a sound wave.
the frequency of the sound wave is the same as the frequency of the ac so by controlling the frequency of the ac you csn alter the sound wave produced

Question 9

what is the generator effect

Answer 9

the induction of a potential difference and current if a complete circuit, in a wire which is moving relative to a magnetic field , or experiencing a change in magnetic field