The Instrument whose deflection is given by the expression

The Instrument whose deflection is given by the expression θ ∝ I² dm/ dθ is known as:

1. electrodynamic type
2. repulsion type
3. electrostate type
4. attraction type

The instrument whose deflection is given by the expression θ ∝ I² dM/dθ is known as electrodynamic type.