29.16 - Sample problem: primary winding in a transformer
Low-voltage devices like the game console above typically run on direct current, so the power converter would not only transform the potential
difference, but also convert AC to DC. Here, we only consider the AC transformer part of the power converter.
Variables
What is the strategy?
- State the turns ratio equation.
- Solve for the number of primary loops and evaluate.
Physics principles and equations
The turns equation for transformers is
Step-by-step solution
We solve the turns equation for N 1 , then evaluate.
A video game console operates at a
potential difference of 9.00 V. The
potential difference supplied by the
power receptacle is 120 V AC. A
transformer is used to convert one
voltage to the other. If the secondary
coil of the transformer (the 9.00 V
side) has 1000 loops, how many
loops does the primary coil have?
primary potential difference V 1 = 120 V
secondary potential difference V 2 = 9.00 V
primary number of loops N 1
secondary number of loops N 2 = 1000
Step Reason
1. turns equation
2. solve for number of primary loops
3. evaluate
29.17 - Interactive problem: configuring a transformer
Here, we simulate a transformer.
An alternating potential difference across the primary
winding on the top creates a magnetic field that
passes through the iron core to the secondary
winding on the bottom. This magnetic field induces an
emf in the bottom coil. The value of the potential
difference across the resistor in the bottom,
secondary circuit (equal to the induced emf) is
displayed on an oscilloscope. You can turn the dial on
the oscilloscope to change the scale of the display.
The height of a grid box equals the setting on the dial.
Your task is to determine the maximum positive
potential difference in the top, primary circuit using
information you glean from the simulation. We use the word “maximum” because
The large cylindrical transformers on the left of this photo convert electricity from
350,000 V to 15,000 V at an electrical substation.