A series circuit is supplied from a variable–frequency source that maintains

PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

A series

LCR

circuit is supplied from a variable–frequency source that maintains

V_{\text{rms}} = 120\,\text{V}

. With the frequency initially set at

90\,\text{Hz}

the rms current is

2.0\,\text{A}

. On adjusting the frequency, the current rises to

4.0\,\text{A}

. The resistance in the circuit is

R = 30\,\Omega

. (i) Calculate the impedance of the circuit at

90\,\text{Hz}

. (ii) Write the value of the impedance when the current is

4.0\,\text{A}

. (iii) Determine (a) the percentage rise in current and (b) the percentage decrease in impedance when the frequency is tuned from

90\,\text{Hz}

to the value that produces the larger current.