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An electric lamp is connected in series with a long solenoid of copper with air core. When the circuit is joined to AC source, the bulb lights up giving a bright glow. Now an iron rod is inserted inside the solenoid, the brightness of the bulb,increases or decreases????

An electric lamp is connected in series with a long solenoid of copper with air core. When the circuit is joined to AC source, the bulb lights up giving a bright glow. Now an iron rod is inserted inside the solenoid, the brightness of the bulb,increases or decreases????

Grade:12th pass

2 Answers

Vikas TU
14149 Points
3 years ago
The brightness will be increased as the core now would be acting as a strong conductor and will now behave as a permanent magnet hence the magnetic field lines increases and hence emf increases and current increases. This leads to increase in the brightness of the bulb.
Prabhjot
13 Points
3 years ago
When the iron rod is inserted in the solenoid, the bulb will dim. It's brightness will decrease. 
As rod is inserted, magnetic field inside the solenoid increases. And I is indirectly proportional to this. Therefore I will decrese and bulb will glow dimmer.
Also the solenoid will now intake more I (current). Thus the bulb will get less current and it's brightness will DECREASE.

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