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I've been presented with this question:

The coil is connected across a 360 V, 60 Hz supply and potential difference of 30 V is measured across a coil when a current of 3A flows through the coil. When an alternating current of 5A flows through the coil at 45 Hz, the potential difference is 210 V across the coil. calculate:

a) the total current,
b) the power dissipated, and
c) the power factor of circuit.

What I've done thus far is:

  1. calculated the current with the 45Hz source
  2. gotten XL with the 45Hz source
  3. calculated the inductance for the 45Hz source
  4. used the ratio of the frequencies to calculate XL and Z for the 60Hz source
  5. calculated the current
  6. used the current and previously calculated XL to get the power
  7. used Z to calculate VA power and then got the power factor

My final answers are I = 6.53 A; P = 426.51 W and PF = 0.18.

I'm pretty sure that what I've done is incorrect. Could anyone assist? Should the values have a complex notation?

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    \$\begingroup\$ the problem question is really cryptic. it is unclear if the three values are to be calculated for 60Hz or for 45Hz. .... there is also an inconsistency in wording which makes the description unclear ... when a current of 3A flows and when an alternating current of 5A flows .......... where did this question come from? ... is this possibly a "trick" question? \$\endgroup\$
    – jsotola
    Commented Mar 15, 2018 at 4:44
  • \$\begingroup\$ Hi @jsotola, this is a 12-mark question in one of my university assignments. I'm not sure what they want either. I have asked someone who did this last year to please clarify as well and will post as soon as they get back to me. \$\endgroup\$
    – Naynay
    Commented Mar 15, 2018 at 6:33
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    \$\begingroup\$ can we assume 'the coil' and 'a coil' are two different coils? \$\endgroup\$
    – Neil_UK
    Commented Mar 15, 2018 at 6:42
  • \$\begingroup\$ @Neil_UK I have a funny feeling they are the same coil. Well, I hope they are. If not, my calculations are incorrect \$\endgroup\$
    – Naynay
    Commented Mar 15, 2018 at 7:48
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    \$\begingroup\$ @BrianDrummond I did calculate it, and used it in conjunction with Z to calculate XL \$\endgroup\$
    – Naynay
    Commented Mar 15, 2018 at 12:39

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