Transmitting Electricity. Learning Objectives Recall the parts of the national grid. Describe what a...
-
Upload
kimberly-griffin -
Category
Documents
-
view
213 -
download
0
Transcript of Transmitting Electricity. Learning Objectives Recall the parts of the national grid. Describe what a...
Learning Objectives• Recall the parts of the national grid.
• Describe what a transformer does.
• Use the turns ration equation to predict the missing voltage or number of turns.
The National Grid• All across the UK a network of pylons and
cables distribute electricity to our houses.
Transformers• The voltage of an alternating current can be
changed using a transformer.
• A step-up transformer increases voltage.
• A step-down transformer decreases voltage.
Why Change Voltage?• Voltage is increased as it is transmitted
through the national grid.
• High voltage is very dangerous but reduces energy lost through heat.
• Voltage is reduced to 230 V before electricity is supplied to homes.
RULE TO REMEMBER...
• High = Low = Less energy wasted as Voltage Current heat
To know how an electric current can be generated in a wire.
A transformer where the voltage rises is called a step-up transformer
To know how an electric current can be generated in a wire.
A transformer where the voltage falls is called a step-down transformer
To know how an electric current can be generated in a wire.
Because transformers rely on induction (changing fields), they only work with alternating current (a.c.)
Direct or alternating current?
The Transformer Equation
Primary voltage
Secondary voltage
No. of turns on Primary coil
No. of turns on Secondary coil=or
Vp =Vs
Np
Ns
To know how an electric current can be generated in a wire.
Example 1A transformer has 1000 turns on its primary coil
and 3000 turns on its secondary. 30 V is applied across the primary coil. What is its output?
S
P
S
P
N
N
V
V
3000
100030
SV
33.030
SV
33.0
1
30SV
330
SV
303SV
90SV V
To know how an electric current can be generated in a wire.
Example 2A transformer has 3800 turns on its primary and 100
turns on its secondary coil. Its output voltage is 6 V.a) Is it a step up or step down transformer?b) Calculate the input voltage.c) Explain why this could be suitable for charging
a mobile phone.
To know how an electric current can be generated in a wire.
a) It is a step down transformer.
b) c) Mains voltage is
230V so this transformer is suitable for stepping down the voltage to a safe level for charging a mobile phone.
s
p
s
p
N
N
V
V
100
3800
6pV
386
pV
638PV
228PV V
Vs
Primary turns Np
Secondary turns Ns
Primary voltage Vp
Secondary voltage Vs
Step up or step down
100 20 3
400 10,000 10
50 240 12
5,000 33,000 11,000
Vp
Ns
Np=
Copy and complete the table