Question Detail

MTH 102 PHY 102 Past Questions Objective Question

Question

The resonant frequency of a circuit is 1000 KHz. If each of capacitance and inductance in the circuit is reduced by 5, the resonant frequency will be:

Options
A 1000KHz
B 2000KHz
C 100.0KHz
D 5000.0KHz
Correct Answer
Correct Answer

Option D is the correct answer.

Detailed Explanation

Here are the steps to solve this type of problem step-by-step:   Step 1: Recall the Resonant Frequency Formula The resonant frequency $f$ of an $LC$ circuit depends on inductance $L$ and capacitance $C$:   $$f = \frac{1}{2\pi \sqrt{L C}}$$ Step 2: Express the New Values in Terms of the Old Ones
  • Both $L$ and $C$ are reduced by a factor of 5:   $$L' = \frac{L}{5}$$ $$C' = \frac{C}{5}$$
Step 3: Set Up the Formula for the New Resonant Frequency ($f'$) Substitute $L'$ and $C'$ into the original formula:   $$f' = \frac{1}{2\pi \sqrt{\left(\frac{L}{5}\right) \left(\frac{C}{5}\right)}}$$ Step 4: Simplify the Denominator
  • Multiply inside the square root: $\frac{L}{5} \times \frac{C}{5} = \frac{LC}{25}$
  • Take the square root of the denominator: $\sqrt{\frac{LC}{25}} = \frac{\sqrt{LC}}{5}$
Step 5: Relate the New Frequency ($f'$) to the Original Frequency ($f$) Simplify the fraction:   $$f' = 5 \times \left( \frac{1}{2\pi \sqrt{LC}} \right) = 5 \times f$$ Step 6: Calculate the Final Answer
  • Multiply your initial resonant frequency ($1000\text{ kHz}$) by $5$ to get the new frequency!

Hint

Recall the formula for resonant frequency. Consider how changes in L and C affect the frequency. The wording 'reduced by 5' likely implies a change by a factor, which leads to a division of the original frequency to match the options.

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