A coil and a bulb are connected in series with a 12 volt direct current source. A soft iron core is now inserted in the coil. Then

Options

A. The intensity of the bulb remains the same
B. The intensity of the bulb decreases
C. The intensity of the bulb increases
D. Nothing can be said

Answer

To analyze the situation described in the question, we will break down the problem step by step.

### Step 1: Understand the Circuit Configuration
We have a coil (inductor) and a bulb connected in series with a 12V direct current (DC) source.

**Hint:** Identify the components in the circuit and their arrangement.

### Step 2: Insert the Soft Iron Core
When a soft iron core is inserted into the coil, the inductance of the coil increases because soft iron has high magnetic permeability.

**Hint:** Recall how the presence of a magnetic material affects inductance.

### Step 3: Analyze the Effect of Inductance on DC Circuit
In a DC circuit, inductance affects the circuit only during the transient state (when the circuit is first closed). Once the current reaches a steady state, the inductor behaves like a short circuit (zero reactance).

**Hint:** Remember that in a DC circuit, after the initial transient response, the inductive reactance is effectively zero.

### Step 4: Determine the Effect on Current (Intensity)
The current (intensity) in a DC circuit is determined by Ohm's Law:
\[ I = \frac{V}{R} \]
where \( I \) is the current, \( V \) is the voltage, and \( R \) is the total resistance in the circuit. Since the inductive reactance is zero in a steady state, the increase in inductance does not change the resistance of the circuit.

**Hint:** Consider how Ohm's Law applies in this situation.

### Step 5: Conclusion
Since the resistance of the circuit remains unchanged and the inductive reactance does not affect the current in a steady state, the intensity of the bulb remains the same after inserting the soft iron core.

**Final Answer:** The intensity of the bulb remains the same.