Electromagnetic Induction Flashcards
State
Lenz’s Law.
the direction of an induced voltage is always such to oppose the change that caused it
What are the two ways in which a voltage can be induced in a circuit with no cell?
(using magnetism)
- A conductor must move in a magnetic field so as to cut the field lines
or - The magnetic field around a conductor must be changing
How could you increase the induced voltage when a conductor is moving in a magnetic field?
(3 ways)
- increase the speed at which the conductor moves
- increase the strength of the magnet
- increase the amount of conductor in the field (more turns of wire)
How could you increase the induced voltage when the magnetic field around a conductor is changing?
- increase the rate of change of field
- increase the strength of the field (stronger magnet)
- increase the amount of conductor in the field (more turns of wire)
How would you reverse the induced voltage when a conductor is moving in a magnetic field?
reverse the motion of the conductor
How could you reverse the induced voltage when a magnetic field around a conductor is changing?
reverse the direction of the changing field
What can
Fleming’s Right Hand Rule assist with?
induction
What do the fingers represent for
Flemings Left and Right Hand Rules?
Thumb - Thrust/motion/force
First Finger - Field
Second Finger - Current
What do microphones do?
(general explanation + 4 steps)
They convert the pressure variations in sound waves into variations in current in electrical circuits.
- Sound waves cause variations in air pressure.
- The pressure variations make a diaphragm vibrate.
- The diaphragm moves a coil of wire backwards and forwards.
- This uses electromagnetic induction to produce a varying current.
What do loudspeakers do?
(general explanation + 3 steps)
Convert variations in electrical current into sound waves.
- The varying current flows through a coil that is in a magnetic field.
- This causes a force on the coil which moves backwards and forwards as the current varies.
- The coil is connected to a diaphragm and the movements of this produces sound waves.
How does a transformer work?
(model answer, 7 steps)
- An alternating voltage is applied to the primary coil.
- This causes an alternating current to flow in the primary coil.
- The current in the primary coil creates a magnetic field in the iron core.
- The iron core directs the magnetic field through the secondary coil.
- The current is alternating so this means that this magnetic field is continually changing.
- The changing magnetic field through the secondary coil induces a voltage in the secondary.
- The ratio of the primary and secondary voltages is equal to the ratio of the number of turns on the primary and secondary coils.
What equation links
voltage and number of turns of the primary and secondary coils of a transformer?
Vs / Vp = Ns / Np
What equation links
current and voltage of the primary and secondary coils of a transformer?
IpVp = IsVs
What is the voltage of the mains in the UK?
~ 230V
(ac)
What is the frequency of the mains in the UK?
(frequency of change of current)
50Hz
What kind of current do cells and batteries supply?
dc
(direct current)
current always flows in the same direction
What are some key safety points to consider when working with the mains?
(5 points)
- never overload mains sockets
- never connect an appliance with a broken case or frayed cables
- be careful with mobile phone chargers - they can overheat
- never use cheap imitation electronics - they are likely to be unsafe
- never leave an extension reel coiled when in use
What are the three wires in a plug?
- live
- neutral
- earth
What does the live wire do in a plug?
provides the ‘push’ (and pull) to supply current
What does the neutral wire do in a plug?
completes the circuit
What does the earth wire do in a plug?
acts as a safety feature for metal appliances
What do plugs have to make them safe to use?
(5 things)
- a plastic or rubber case which does not conduct electricity
- brass pins (because brass is a good conductor)
- the correctly sized fuse
- an earth pin that prevents electric shock
- a cable grip that holds the cable in place and prevents the three wires from becoming disconnected
What is a
fuse?
a piece of wire which gets hot and eventually melts if too much current flows through it
(this breaks the circuit)
a circuit breaker performs a similar function
What equation links
power, current and resistance?
P = IIR
What equation links
voltage, current and resistance?
V = IR
What equation links
power, current and voltage?
P = IV
