6.8 The transformer Flashcards
What do transformers do
Transformers increase or decrease the voltage of alternating current electrical power supplies. Transformers do not work with direct current
How do transformers work
- The primary coil produces a magnetic field
- This magnetic field links with the secondary coil
- With alternating current the primary magnetic field varies continues
- because of this the magnetic flux linkage in the secondary coil also varies continuously
- the change of the magnetic flux linkage induces an emf in the secondary coil
What is the circuit symbol for a transformer
3 l 8
3 l 8 just imagine this is a picture :/
3 l 8
Why are the coils in a transformer wrapped around an iron core
To increase magnetic flux
The core is made from thin laminated iron sheets which are insulated from one another. Why is this
This is done to reduce energy losses. Most transformers become warm meaning that they waste electrical energy that is transferred to internal energy stores when the transformer is in operation. Large transformers need special cooling systems to prevent them overheating.
What is the transformer equation for an ideal transformer
Vs / Vp = Ns / Np
V = voltage
N = number of turns
What is another equation for an ideal transformer
IsVs = IpVp
What is the transformer equation in practice and what does this mean in terms of energy
IsVs < IpVp
This is because in practice there are always energy losses
An ac voltage in a resistor will produce what in the resistor and how can we describe the alternation
An ac current will be produced in the resistor and the alternation will always be sinusoidal
What is the equation for sinusoidal alternations
V = V0sin2pift
I = I0sin2pift
f in this case is the alternating frequency
What is the frequency we usually deal with and whynis this
We usually deal with frequencies of 50Hz. This is because this is the frequency of mains voltage supply in the uk
For graphs of mains ac voltage, for the graphs where there is a maximum of V0 and I0 what are the average values of V and I
For their respective graphs the average values of V and I is zero
The power graph represents the power dissipated in the resistor where there is a maximum value of P0. What is the average value of P
The average value of P is 1/2 I0V0
Since Pav = 1/2 I0V0 Derive another useful equation
sub in I = V0/R Pav = 1/2 V0^2/R
Since a dc supply of pd will produce a power in a resistor of V^2/R
v^2/R = 1/2 V0^2/R this can be simplified to
V = V0/√2
The equation V = V0/√2 is known as what
The root mean square value of the potential difference. It is called this because it is obtained by taking the square root of the mean square potential difference. It is usually quoted when referring to alternating voltage
