Q. State
faraday’s law
Ans: a) Whenever
the magnetic flux linking a circuit changes an emf is always induced in it.
b) The
magnitude of such an emf is proportional to the rate of change of flux linkages.
Q. How do you
find the direction of force produced using Fleming’s left hand
rule?
Ans: The thumb, the forefinger and the middle finger
of the left hand are held so that these fingers are mutually
perpendicular then
Forefinger –>field
Thumb->motion (due to force)
Middle finger-> current
Q.What is the
basic principle of operation of d.c
motor?
Ans: The basic
principle of operation of d.c motor is that a current carrying conductor placed in a magnetic field, experiences a
force tending to move it.
Q.What is the
purpose of interpoles in modern d.c machine?
Ans: In modern d.c machines commutating poles or
interpoles are provided to improve commutation i.e. to reduced sparking at
brushes.
Q.What is the
use of commutator and brush in a d.c
machine?
Ans: The commutator converts the alternating emf
into unidirectional or direct emf.
The brushes are mainly used to collect current from
the commutator.
Q.Write down
the voltage equation of a d.c motor?
Ans: Voltage equation of a d.c motor is given by
V=Eb+IaRa
Where V-applied voltage
Eb-back emf
Ia- armature current
Ra- armature resistance
Q. Why are
carbon brushes preferred for dc machines?
Ans: The high contact resistance carbon brushes help
the current
the coil undergoing commutation to attain its full
value in the reverse direction at the end of commutation. The carbon brushes also
lubricate and give less wear and tear on commutator surface.
Q. How will
you find the direction of emf using Fleming’s right hand rule?
Ans: The thumb, the forefinger and the middle finger
of the right hand are held so that these fingers are mutually
perpendicular then
Forefinger direct–>field
Thumb direct ->motion
Middle finger direct -> current.
Q.What is the
basic principle of a dc generator?
Ans: Basic principle of a dc generator is Faraday’s
law of electromagnetic induction. That is whenever a conductor is moved in
a magnetic field dynamically induced emf is produced in that conductor. Voltage
induced [e=Blv] in volts, where B is flux density, l is effective length of
conductor, v is speed.
Q. How are
hysteresis and eddy current losses minimized?
Ans: Hysteresis loss can be minimized by selecting
materials for core such as silicon steel & steel alloys with low
hysteresis co-efficient and electrical resistivity.
Eddy current losses are minimized by laminating the
core.