# Homework Help: Can someone check my Physics working?

1. Apr 26, 2004

### cseet

Hi all,
can somebody pls check whether or not I'm in the right direction with my workings and answers. If not, can you pls advise why I've gone wrong?

thanks

question 1:
1. An inductor has a 54 ohm reactance at 60 Hz. What is the maximum current if this inductor is connected to a 50 Hz source that produces a 100 Vrms voltage?

L=?
XL = (2 pie f)(L)
54 = (2 pie 60) L
L = 54 / (2 pie 60) = 0.14H

Imax = ?
f = 50 Hz
Vrms = 100V
V max = 100 * sq root of 2

XL = wL
= (2 pie 50) (0.14)
= 43.98 = 44 ohm

therefore
Imax = Vmax / XL
= (100 * sq root 2) / 44 = 3.2A

question 2:

What maximum current is delivered by a 2.2 microF capacitor when connected to a North American outlet where Vrms = 110 V and f = 60 Hz

Imax = ?
Xc = 1 / (wC) = 1 / [(2 pie 60) * (2.2E-6)]
= 1206 ohm
Imax = Vmax / Xc
= (110 * sq root of 2) / 1206
= 0.13A

thanks again
cseet

2. Apr 28, 2004

### Staff: Mentor

Looks good to me.

The only thing I could suggest is that when you wish to give your answer to 2 significant figures (which is great!) to be sure to carry all intermediate calculations to at least 3 figures to minimize any round off error. For example, in problem #1 you round off the inductance to 0.14 when a more accurate answer is 0.143. Wait until the last step to round off your answer to a sensible number of figures.