Electromagnetic Induction Flashcards
What happens when an electrical conductor moves relative to a magnetic field?
A voltage is induced across the conductor
What happens when an electrical conductor when there is a change to the magnetic field that it is placed in?
The voltage is also change
How do you produce an electric current using a magnet and a conductor on a small-scale?
Moving a coil of wire between magnetic poles, moving a magnet within a coil of wire and once a voltage is induced, if there is a complete circuit a current will also be induced
How is electrical current produced on a large-scale?
An electromagnet is rotated around a coil
What factors affect the size of an induced voltage?
The number of turns on the coil of wire, how strong the magnetic field is and the speed of the movement
What is the requirement for an induced potential difference to cause a current flow?
The conductor must form a closed loop or be part of a complete circuit
What can be said about the direction of the magnetic field produced by an induced current?
The direction of the field is such that it opposes the change that induced the current and this change is either the movement of the conductor or a change to the field
What are two way that the generator effect is used to generate different types of current?
In an alternator to produce alternating-current and in a dynamo to produce direct-current
How does a dynamo generate current?
A coil of wire rotates inside a magnetic field, a commutator is used to ensure it continues rotating in the same direction, therefore keeping the current flowing in the same direction
How is electromagnetic induction used in alternators to generate alternating current?
A coil of wire rotates in a magnetic, the end of this coil is connected to slip rings which will cause the current to change direction while rotating and this means a.c is produced
What electromagnetic effect does a microphone take advantage of and how?
The generator effect and it converts the pressure variations in sound waves into alternating current
How do loudspeakers make use of the motor effect?
The motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound
How does a loudspeaker work?
A cone wrapped in a wire is connected to an a.c power supply and is placed in a permanent magnetic field, when current flows through the wire, it creates a magnetic field which interacts with the permanent field and this produces a force which causes the cone to vibrate producing sound
How is the pitch of the sound from a loudspeaker changed?
The frequency of the a.c current is altered and this creates a different frequency of vibrations in the cone
How do microwaves convert sound into electrical signals?
Sound produces pressure variations which cause the diaphragm to vibrate, a coil of wire is connected to the diaphragm, so as the diaphragm moves, the coil also moves, movement in a magnetic field = a p.d is induced and as there is a complete circuit a current is also created
What is the makeup of basic transformer like?
A primary coil and a secondary coil of wire wrapped around an iron core
Why is iron used as the core for a transformer?
It’s easily magnetised
How does a transformer work?
An alternating current flows through the primary coil, this induces a change magnetic field in the core, this changing magnetic field induced an emf, which produces a current in the secondary coil
Why must the current flowing through the primary coil of a transformer be alternating?
For current to be induced in the secondary coil, the magnetic field in the core must be continuously changing and for the magnetic field to be changing, the current in the primary coil must be alternating
What can be said about the electrical power input and output of a 100% efficient transformer?
The electrical power input is equal to the electrical power output
What is the equation linking number of turns with p.d in transformers?
Primary p.d / secondary p.d = primary turns / secondary turns
What is the power equation for transformers with a 100% efficiency?
Vp x Ip = Vs x Is
On a step-down transformer, does the secondary coil have more or fewer turns?
Fewer turns
What is an advantage of a step down transformer in the national grid?
It means that the voltage can be reduced to a value safe enough to be used in houses
Why is it important to have step up transformers in the national grid?
It can increase efficiency, for the same power, higher voltage will lead to a lower current, lower the current, the less energy that is lost and used for transmission across power lines
How does a step up transformer work?
The primary coil has fewer turns, an a.c current produced a magnetic field in the primary coil, the iron core passes the magnetic field to the secondary coil, the magnetic field induces a higher voltage in the secondary coil and power is conserved so this produces a lower current
Where are step-up and step-down transformers used in the national grid?
Step-up transformers are used at power stations, whilst step-down transformers are used domestically
