A transformer's primary coil carries an alternating current. What appears across its secondary coil?
A phone charger's wall plug is swapped for a battery. The transformer sits silent: the phone gets nothing.
A battery supplies direct current: current that always flows one way. This lesson shows why direct current kills the transformer's trick.
A battery is connected to the primary coil, and a current flows.
For an instant the current rises from zero. Then it settles to one steady value.
A steady current makes a steady magnetic field in the core.
The rule from earlier in this topic decides the rest: no EMF is induced while the magnetic field through the conductor is not changing.
The field through the secondary is strong. But it is not changing. So the secondary's EMF is zero.
The output dies the moment the current settles. A transformer connected to a battery gives zero output from then on.
A transformer is connected to a battery. After the current settles, what is the secondary's EMF?
A doorbell transformer is connected to a lantern battery by mistake. After the current settles, what EMF does its secondary show?
The battery's current settles to one steady value.
A steady current makes a steady field in the core.
No EMF is induced while the field through the secondary is not changing.
Zero: the field through the secondary is not changing.
The battery is swapped back for the AC supply. Why does the output return?
The alternating current keeps changing.
So the field in the core keeps changing.
The field through the secondary is changing again, so an EMF is induced.
The output returns because the field through the secondary is changing again.
This is the same transformer that worked a moment ago on AC. One thing changed: the field in the core stopped changing.
Hugo says a transformer will step a battery's 12 V down to 6 V if the turns are right. Is Hugo correct?
Ingrid says the field in the core must keep changing for a transformer to give an output. Is Ingrid correct?
A model-railroad transformer is wired to a car battery by mistake. After the current settles, its output reads zero. Why?
Which supply can run a transformer?
A battery is connected to a transformer's primary. At which moment is an EMF briefly induced in the secondary?