Which of the following factors improve commutation in a dc machine ? 1. High contact resistance of brushes 2. High inductance of the coils undergoing commutation 3. Shifting of brushes in the direction of rotation for a generator and in the opposite direction For a motor 4. Narrow width for the commutation bars Select the correct answer using the codes given below : Codes :

• A.  1, 2, and 3
• B.  1 and 3
• C.  1, 2 and 4
• D.  2, 3 and 4

Answer: (B)