Relative to the direction of rotation, which...

🔍 Key Concepts

• Commutating (inter) poles are used to improve commutation and reduce sparking at the brushes in a D.C. motor • Interpoles are placed between the main field poles and their polarity is related to the direction of rotation and the armature current • The polarity of a commutating pole is chosen so that it aids commutation by opposing the armature reaction under the brushes

💭 Think About

• Picture the direction of rotation and identify which main pole is just ahead of the brush position and which is just behind it • Think about whether the commutating pole needs to have the same or opposite polarity as the adjacent main pole in order to neutralize armature reaction at the brushes • Relate the term "preceding" and "following" to the physical rotation of the armature: which pole does the conductor pass first, and which does it pass next, as it turns?

✅ Before You Answer

• Be clear on what preceding and following mean relative to the actual direction of rotation drawn on a sketch • Confirm whether inter/commutating poles are connected in series with the armature, which makes their polarity depend on armature current direction and thus rotation • Verify which main pole (preceding or following) must have the same polarity as the commutating pole for proper commutation with the given rotation direction

Relative to the direction of rotation, which statement is true concerning a D.C. motor commutating pole polarity?

The commutating pole has the same polarity of the main pole following.

The commutating pole has the same polarity of the interpole following.

The commutating pole has the same polarity of the main pole preceding.

The commutating pole has the same polarity of the interpole preceding.

🔍 Key Concepts

💭 Think About

✅ Before You Answer