A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when:

  • Option 1)

    an iron rod is inserted in the coil.

  • Option 2)

    frequency of the AC source is decreased.

  • Option 3)

    number of turns in the coil is reduced.

  • Option 4)

    a capacitance of reactance XC = XL is included in the same circuit.

 

Answers (1)

As we discussed in 

As the iron rod is inserted the magnetic field inside the coil is magnetices the iron increasing the magnetic field inside it. hence the inductance of the coil increases. the inductive reactance of the coil increase. As a result a larger traction of the applied Ac voltage appears across the inductor leaving less voltage across the buld.

Brightness of the bulb decreases


Option 1)

an iron rod is inserted in the coil.

Option is correct

Option 2)

frequency of the AC source is decreased.

Option is incorrect

Option 3)

number of turns in the coil is reduced.

Option is incorrect

Option 4)

a capacitance of reactance XC = XL is included in the same circuit.

Option is incorrect

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