# Analogue Circuits Question -- AC and DC currents through a coil

• IronaSona

#### IronaSona

Summary:: .

Hi ,so am currently doing homework , and was wondering if anyone could tell me if i have done my calculations correctly ,because am not 100% sure that i have answer to those 2 questions correctly .If i have went somewhere wrong if you could tell me where and how i could fix it ,that would be great. Thank you.

#### Attachments

• IronaSona
You are a bit more consistent than the examiner.
The questioner wrongly specifies lower case units, without a space; 100v, 250w, 50hz.

For units named after a person, such as Volta, Watt or Hertz;
the initial should be spaced and upper case; 100 V, 250 W, 50 Hz;
while the spelled out unit should be all lower case; 100 volt, 250 watt, 50 hertz.

• • berkeman and IronaSona
The answer for the capacitor case looks ok, though I haven't check the arithmetic operations.

The answer for the coil contains too many typos and inconsistencies, for example you write that ##Z=\sqrt{R^2+X_L^2}## and then later you seem to imply that ##Z=X_L##.

The answer for the capacitor case looks ok, though I haven't check the arithmetic operations.

The answer for the coil contains too many typos and inconsistencies, for example you write that ##Z=\sqrt{R^2+X_L^2}## and then later you seem to imply that ##Z=X_L##.

is this better ?

#### Attachments

Nope you basically do the same mistake. The correct way to go is as follows:
The coil's impedance at 60hz is ##Z=\frac{140}{2}##. Use this and the equation ##Z=\sqrt{R^2+X_L^2}## to correctly determine the reactance ##X_L## at 60 hz and from that the value of L.
Then you should NOT forget the ohmic resistance of the coil when you calculate the new reactance and new impedance at 50hz

Nope you basically do the same mistake. The correct way to go is as follows:
The coil's impedance at 60hz is ##Z=\frac{140}{2}##. Use this and the equation ##Z=\sqrt{R^2+X_L^2}## to correctly determine the reactance ##X_L## at 60 hz and from that the value of L.
Then you should NOT forget the ohmic resistance of the coil when you calculate the new reactance and new impedance at 50hz

#### Attachments

There are still some typos but now what you do seems correct. Havent checked the arithmetic.

• IronaSona