# Homework Help: It's me again. need somebody to check my answer

1. Apr 7, 2004

### cseet

Hi all,

it's me again... sorry but this is the only place where I learn most of my physics from... pls kindly check my answer and for the last part... I found the angle but don't know how to convert it to (rad)... pls guide me...thanks

A series RCL circuit with L= 6.5 mH, C=3.7uF, and R = 5.5ohm is driven by a generator with a maximum emf of 197 V and a variable angular frequency w.

(a) Find the resonant frequency . (Unit: rad/s)

(b) Find I(rms) at resonance when w=7.0E3 rad/s . (Unit: A)

25.3 A

(c) Find X(c) when w=7.0E3 rad/s. (Unit: ohm)

38.6 ohm

(d) Find X(L) when w=7.0E3 rad/s. (Unit: ohm)

45.5 ohm

(e) Find Z when w=7.0E3 rad/s. (Unit: ohm)

8.82 phm

(f) Find I(rms) when w=7.0E3 rad/s. (Unit: A)

15.8 A

phase angle = inverse tan ((45.5-38.6) / 5.5) = 51.4

answer: I found the angle to be 51.4 degrees but how do I convert it to unit - rad?

thanks
cseet

2. Apr 7, 2004

### Severian596

If I'm not mistaken this is a conversion between degrees and radians.

$$\frac{2 \pi}{360} = \frac{x}{51.4}$$

and solve for x. Don't factor out $$\pi$$, use it in your answer. For example $$x = 0.98 \pi$$

Last edited: Apr 7, 2004
3. Apr 7, 2004

### Chen

All answers are correct (good job!) except for (b) which I cannot confirm nor deny. I still don't understand the meaning of "I(rms) at resonance when w=7.0E3 rad/s" when the only resonance frequency is 6.45E3 rad/s. If they only want you to find I(rms) at w=7.0E3 rad/s, then the answer should be the same as (f), 15.8A.