Chapter 13 Flashcards
How to produce an electric current by the relative movement of a magnet and a conductor on a small scale- in the laboratory
Coil between opposite magnetic poles
How to produce an electric current by the relative movement of a magnet and a conductor in the large-scale generation of electrical energy
Generators are the devices that transfer kinetic energy into electric energy
A power station uses a turbine to turn a huge alternator.
The burning of fuels in boilers is used to he’s water and convert it to steam, which turns a turbine.
The turbine connected to a powerful magnet (electromagnet) inside a generator.
As turbine spins, the magnet spins with it, inducing a large p.d and ac in the coils.
Recall the factors that affect the size and direction of an induced potential difference and describe how the magnetic field produced opposes the original change
Size= use a stronger magnetic field, have a greater number of turns on the coil and move the magnet faster Direction= reversing direction of current or reversing direction of magnetic field
How is electromagnetic induction used in alternators
A generator consists of a coil of wire that is rotated inside a magnetic field. As the coil turns, a voltage is induced in the wire. The ends of the coil are connected to slip rings. Electrical contact with an external circuit is made using carbon brushes, which press on the slip rings. A generator like this produces alternating current, and is often called an alternator
How is electromagnetic induction used in dynamos
Dynamos generate direct current
They have split ring commutator, this swaps the connection every half turn to keep the current flowing in the same direction
How can an alternating current in one circuit induce a current in another circuit in a transformer
The changing current produces a changing magnetic field. This induced an alternating voltage in the secondary coil. This induces an alternating current in the circuit connected to the secondary coil
What can a transformer do?
change the size of an alternating voltage
What is the ratio equation to find out the missing voltage or missing number of turns
Vp Np
=
Vs Ns
Why in the national grid is electrical energy transferred at high voltages from power station and then transferred at lower voltages in each locality for domestic uses
It improves the efficiency by reducing heat loss in transmission lines
Why are step up and step down transformers used in the transmission of electricity in the national grid
Step up transformers are used at power stations to produce the very high voltages needed to transmit electricity through the national gird power lines. These high voltages are too dangerous to use in the home, so step down transformers are used locally to reduce the voltage to safe levels.
What is the power equation (for transformers with 100% efficiency)
Vp x Ip = Vs x Is
Explain the advantages of power transmission in high-voltage cables
It minimises the power loss due to resistance in conductors. Voltage is inversely proportional to current. Increasing the voltage decreases the current, which decreases the power loss
What is a transformer
A transformer is a device that changes (transforms) and alternating potential difference (voltage) from one value to another value.
Explain how a transformer works
The primary coil is connected to an AC supply.
An alternating current passes through a primary coil wrapped around a soft iron core.
The changing current produces a changing magnetic field.
This induced an alternating voltage in the secondary coil.
This induced an alternating current in the circuit connected to the secondary coil.
what is there no…………..between the primary and secondary coils
There is no electrical connection between the primary and secondary coils
What current is needed for the transformer to work
Transformers only work if AC is supplied to the primary coil. If DC was supplied, there would be no current in the secondary coil.
What happens as the current in the primary coil increases steadily or decreases steadily
There is a constant voltage induced in the secondary coil
What happens as the voltage in the primary coils reaches maximum strength
the voltage induced in the secondary coil is at its weakest (zero volts)
What does a transformer consist of
A soft iron coil with two coils wound around it which are not connected to one another
What are carbon brushes
Brushes that make continuous contact between the external circuit and the slip rings
What are slip rings
Dynamos or ac motors
Electricity out of spinning coil from dynamos or into coil if it was a motor
What is a commutator
Allow motor to spin
Explain the action of a microphone
Sound waves hit a flexible diaphragm that is attached to a coil of wire. This means as the diaphragm(and so the coil) moves, a current is generated in the coil. The movement of the coil (and so the generated current) depends on the properties of the sound wave (louder sounds make diaphragm move further).
This is how microphones can convert the pressure variations of a sound wave into variations in current in an electric circuit.
Diaphragm attached to magnet
Explain the action of loudspeakers and headphones
Loud speakers are like microphones but in reverse.
In a loud speaker the diaphragm is Replaced with a paper cone.
The coil is wrapped around on pope of a permanent magnet so the ac signal causes a force on the coil which moves the cone .
When the current is reversed, the force acts in the opposite direction.
These movements make the cone vibrate, which makes the air around the cone vibrate and creates the variations in pressure that cause a sound wave.
What is a generator
Huge cylinder wound with coils of copper wire
