In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?
Option (a): If only a resistor is present there, the rms current or max current doesn’t change with frequency. This is incorrect.
Option(b):
Now, the rms current is given by:
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As the source doesn’t change Vrms doesn’t change. Note that Z is the impedance or reactance given by:
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Where XL is the inductive reactance, XC is the capacitive reactance and R is the resistance of the resistor.
Now, in this option there is no capacitor and hence, XC must be zero. Now,
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Now, the inductive reactance is given by:
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where f is the frequency and L is the inductance.
From the above equation we can see that, inductive reactance and frequency have a direct relation. So, on increasing the frequency, the inductive reactance increases. Thus, the impedance (
) increases. Hence, Irms decreases. Thus, this option is incorrect.
Option(c):
Now, in this option there is no capacitor and hence, XL must be zero. Now,
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Now, the capacitive reactance is given by:
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where f is the frequency and C is the capacitance.
From the above equation we can see that, capacitive reactance and frequency have an inverse relation. So, on increasing the frequency, the capacitive reactance decreases. Thus, the impedance (
) decreases. Hence, Irms increases. Thus, this option is correct.
Option (d):
Now, in this option there is no capacitor and hence, XL must be zero. Also, R is zero. Now,
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Now, the capacitive reactance is given by:
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where f is the frequency and C is the capacitance.
From the above equation we can see that, capacitive reactance and frequency have an inverse relation. So, on increasing the frequency, the capacitive reactance decreases. Thus, the impedance (
) decreases. Hence, Irms increases. Thus, this option is correct.