# Series Coupling

When two coils of self-inductances L1 and L2 are connected in series, two types of connection are possible:
1. Series Aiding Connection

(a)

(b)

(c)
Series Aiding Connections

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1. Series Opposing Connection
In this connection, the two coils are connected in series such a way that their induced e.m.f.â€™s are of opposite polarities.
Series Opposing Connections

Here, total inductance = (L1 + L2 â€“ 2M)

# Parallel Coupling

When two coils of self-inductances L1 and L2 are connected in parallel, two types of connection are possible:
1. Parallel Aiding Connection
In this connection, the two coils are connected in parallel such a way that their induced e.m.f.â€™s are of same polarities.

Parallel Aiding Connections

Here, total inductance
1. Parallel Opposing Connection
In this connection, the two coils are connected in parallel such a way that their induced e.m.f.â€™s are of opposite polarities.

Parallel Opposing Connections

Here, total inductance
It can be derived in the same way as done for parallel opposing connection.