The correct answer is: A. Lap winding
A lap winding is a type of winding used in DC generators. It is characterized by having the armature conductors connected in parallel between the commutator segments. This type of winding has the advantage of producing a higher e.m.f. than a wave winding.
A wave winding is a type of winding used in DC generators. It is characterized by having the armature conductors connected in series between the commutator segments. This type of winding has the advantage of being less expensive to manufacture than a lap winding.
The e.m.f. produced by a DC generator is given by the following equation:
$E = \frac{PZN}{A}$
where:
- $E$ is the e.m.f. in volts
- $P$ is the number of poles
- $Z$ is the number of armature conductors
- $A$ is the number of parallel paths
In a lap winding, there are as many parallel paths as there are armature conductors. In a wave winding, there are only two parallel paths. Therefore, a lap winding will always produce a higher e.m.f. than a wave winding, given the same number of poles and armature conductors.
The other options are incorrect because:
- Option B is incorrect because a wave winding will always produce a lower e.m.f. than a lap winding, given the same number of poles and armature conductors.
- Option C is incorrect because both lap and wave windings can produce a high e.m.f., depending on the number of poles and armature conductors.
- Option D is incorrect because the e.m.f. produced by a DC generator is only dependent on the number of poles, armature conductors, and the number of parallel paths. Other features of design, such as the type of insulation used, do not affect the e.m.f.