Solve Mutual Inductance Homework: V_0cosωt, L, M, R, i_1 & i_2

In summary, the conversation discusses the relationship between a coil with self inductance L1 and a second coil with self inductance L2 and resistance R. The coefficient of mutual inductance is M, and the second coil is short-circuited while the first coil is connected to a voltage source V0cosωt. The conversation then goes on to find an expression for the current in the second coil as a function of time, using Laplace domain and converting back to the real world. The final expression for the current is -Mv0/L1Rωcosωt.
  • #1
papkin
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Homework Statement


A coil of self inductance [tex]L_{1}[/tex] is coupled to a second coil of self inductance [tex]L_{2}[/tex] and resitance [tex]R[/tex]. The coefficient of mutual inductance is [tex]M[/tex]. The second coil is short circuited whereas the first coil is connected via a switch, to a voltage source [tex]V_{0}cos \omega t [/tex]

Homework Equations


The switch is closed at time t = 0. Find an expression for the current which then flows in the second coil, as a function of time.

The Attempt at a Solution


[tex] V_{0}cos \omega t = L \frac {di_{1}}{dt} [/tex]
[tex] M \frac {di_{1}}{dt}= - i_{2}R [/tex]
Transferring into Laplace domain:
[tex] I_{1}(s) = \frac {v_{0}}{L_{1}} \frac {1}{s^{2}+\omega^{2}}[/tex]
[tex] I_{2}(s) = \frac {-Mv_{0}}{L_{1}R} \frac {1}{s^{2}+\omega^{2}} [/tex]
and back to the real world:
[tex] i_{2} = \frac {-Mv_{0}}{L_{1}R\omega} sin \omega t [/tex]
and that just doesn't feel right.

Thanks, in advance.
EDIT: Sorry, lost an s somewhere along the way, got [tex] \frac {-Mv_{0}}{L_{1}R} cos \omega t [/tex] now.
I think that's correct, but wouldn't mind somebody reassurance by someone more experienced.
 
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  • #2
The Attempt at a Solution V_{0}cos \omega t = L_{1} \frac {di_{1}}{dt} M \frac {di_{1}}{dt}= - i_{2}R Transferring into Laplace domain: I_{1}(s) = \frac {v_{0}}{L_{1}} \frac {1}{s^{2}+\omega^{2}} I_{2}(s) = \frac {-Mv_{0}}{L_{1}R} \frac {1}{s^{2}+\omega^{2}} and back to the real world: i_{2} = \frac {-Mv_{0}}{L_{1}R\omega} sin \omega t and that just doesn't feel right.Thanks, in advance.EDIT: Sorry, lost an s somewhere along the way, got \frac {-Mv_{0}}{L_{1}R} cos \omega t now.I think that's correct, but wouldn't mind somebody reassurance by someone more experienced.
 

1. What is mutual inductance?

Mutual inductance is a property of two circuits in which a change in current in one circuit induces a voltage in the other circuit. It is denoted by the symbol M and is measured in Henrys (H).

2. How is mutual inductance calculated?

Mutual inductance can be calculated using the formula M = k√(L1L2), where k is the coupling coefficient and L1 and L2 are the inductances of the two circuits.

3. What is the significance of mutual inductance in circuit analysis?

Mutual inductance plays a crucial role in understanding the behavior of circuits with multiple inductors. It helps in calculating the voltage and current in one circuit due to changes in the other circuit.

4. Can mutual inductance be negative?

Yes, mutual inductance can be negative if the two circuits have opposite orientations or if the current in one circuit is decreasing while the current in the other circuit is increasing.

5. How does mutual inductance affect the voltage across a circuit?

Mutual inductance can cause a voltage drop or a voltage boost in a circuit, depending on the direction of the current and the orientation of the inductors. This effect is known as inductive coupling.

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