# How the total energy of a LC oscillator remains unchanged while placing a coil near the inductor of the LC oscillator?

If the capacitor is initially charged with Q charge and then conected to a inuctor then discharging takes place and the energy stored in electric field gets converted into the energy stored in magnetic field. Energy of a LC oscillator oscillates in the electric field of capcitor and magnetic field of inductor and the energy remains unchanged for ideal case.

Now if we placed a coil near the inductor then with the changing of current magnetic flux associated with the coil also changes and that causes an EMF in the coil and if there is resistance of R with the coil then there is some loss of energy but the energy in LC oscillator remains unchanged.

Where from the energy comes that is lost in the coil?

• Why do you say the energy of the LC oscillator remains unchanged? Wouldn't it make sense that it is the oscillator's energy that is slowly being lost through dissipation? – Philip Jan 5 '20 at 17:59
• I am considering an ideal oscillator. – Sk Asik Ekbal Jan 5 '20 at 18:13
• You don't say whether the coil is open-circuit, short-circuited or connected to something else. If the coil is open circuit there will be no energy dissipation in it. – Philip Wood Jan 6 '20 at 0:04
• No. I mentioned there is a resistance of R. I just wants to know where from the energy comes that is used in the LR ciruit as the energy stored in the LC oscillator remains unchanged. – Sk Asik Ekbal Jan 6 '20 at 2:02

there is resistance of R with the coil then there is some loss of energy but the energy in LC oscillator remains unchanged. Where from the energy comes that is lost in the coil?

The energy dissipated in the RL circuit comes from the energy stored in the inductor and capacitor of the LC circuit. Therefore the energy of the LC circuit does not remain unchanged. It is dissipated in the LR circuit.

In the same way the primary circuit of a transformer transfers energy to the secondary circuit, your LC oscillator is transferring energy to the external coil and dissipated in the resistor. In the case of a transformer, the energy of the primary coil comes from an ac voltage source. If your ideal LC oscillator is not connected to an energy source, the energy comes from the stored energy in the LC circuit, resulting in its oscillation being be damped and eventually cease until all of its stored energy is dissipated in the resistor of the RL circuit.

It should be noted that even without the external coil, there will always be some resistance in the LC circuit to dissipate energy. Even if there were theoretically zero resistance, the LC circuit will lose energy in the form of electromagnetic radiation.

Hope this helps.