What electric phenomenon causes counter EMF (electromotive force) in a coil of
wire in which current has just started to flow?
a. The magnetic field cutting across the coil induces an opposing voltage in the
b. The magnetic field surrounding the coil reverses the polarity of the wire.
The wire leak voltage into the magnetic field.
d. The expansion of the wire cuts across magnetic lines of force.
How is the magnetic field affected when a soft iron core is inserted in a choke coil?
a. Intensifies the magnetic field.
b. Causes the magnetic field to collapse.
Causes the magnetic field to decrease the back electromotive force.
d. Demagnetizes the magnetic field.
When variations of current in one circuit produce voltage (EMF) in another circuit
nearby, the phenomenon is called:
a. Counter electromotive force.
Opposite voltage flow.
d. Direct current flowing in a coil.
In a 60-cycle alternating current, there are _____ impulses per second.