Question 69 of 949
A 2H inductor has negligible resistance and is connected to a 50/π Hz A.C. Supply. The reactance of the inductor is
- A. 200 Ω
- B. 50 Ω
- C. 100/π Ω
- D. 25/π Ω
Correct Answer:
A
Explanation
To determine the reactance of the inductor in this problem, we need to use the formula for inductive reactance, which is given by:
\[
X_L = 2\pi f L
\]
where:
- \(X_L\) is the inductive reactance in ohms (Ω),
- \(f\) is the frequency in hertz (Hz),
- \(L\) is the inductance in henries (H).
### Step-by-Step Explanation
1. **Identify the Given Values**:
- The inductance \(L\) is given as \(2 \, \text{H}\).
- The frequency \(f\) is given as \(50/\pi \, \text{Hz}\).
2. **Substitute the Values into the Formula**:
We can now substitute the values of \(L\) and \(f\) into the formula for inductive reactance:
\[
X_L = 2\pi \left(\frac{50}{\pi}\right) (2)
\]
3. **Simplify the Expression**:
- First, simplify the frequency term:
\[
X_L = 2\pi \cdot \frac{50}{\pi} \cdot 2
\]
- The \(\pi\) in the numerator and denominator cancels out:
\[
X_L = 2 \cdot 50 \cdot 2
\]
- Now, calculate the multiplication:
\[
X_L = 2 \cdot 50 = 100
\]
\[
X_L = 100 \cdot 2 = 200 \, \Omega
\]
4. **Final Result**:
Thus, the reactance of the inductor is \(200 \, \Omega\).
### Explanation of the Options
- **Option A: 200 Ω** - This is the correct answer as we calculated \(X_L\) to be \(200 \, \Omega\).
- **Option B: 50 Ω** - This option is incorrect. It does not match our calculated value and does not take into account the inductance and frequency correctly.
- **Option C: 100/π Ω** - This option is also incorrect. It seems to confuse the relationship between frequency and inductance. The reactance is not simply a division by \(\pi\).
- **Option D: 25/π Ω** - This option is incorrect as well. Similar to option C, it does not reflect the correct calculation of inductive reactance and is not derived from the formula correctly.
### Common Pitfalls
- **Forgetting to use the correct units**: Always ensure that the inductance is in henries and frequency in hertz.
- **Misapplying the formula**: Ensure that you are using the correct formula for inductive reactance and substituting values accurately.
- **Neglecting to simplify**: Sometimes, students forget to simplify expressions, leading to incorrect answers.
### Revision Summary
- The formula for inductive reactance is \(X_L = 2\pi f L\).
- Substitute the values of frequency and inductance carefully.
- Simplify the expression step-by-step to avoid mistakes.
- The correct answer for the reactance of a 2H inductor at \(50/\pi \, \text{Hz}\) is \(200 \, \Omega\).