Find current at high/low frequency

  • Thread starter Thread starter Acuben
  • Start date Start date
  • Tags Tags
    Current Frequency
AI Thread Summary
The discussion focuses on calculating the RMS current from a 45V power supply at different frequencies. For very high frequency, the RMS current is determined to be 225mA, while at very low frequency, it is 450mA. The key concept is that at high frequency, the impedance of the inductor can be approximated as infinite, while at low frequency, the capacitor's impedance is treated similarly. This simplification allows for the elimination of one loop in the circuit for each frequency case. Understanding these impedance behaviors is crucial for accurate calculations in AC circuits.
Acuben
Messages
61
Reaction score
0

Homework Statement


find the rms current delievered by the 45v (rms) power supply when
a) the frequency is very large
and b) the frequency is very small.

answer: a) 225mA, b) 450mA

http://yfrog.com/jucurrentqg

http://img714.imageshack.us/img714/1592/currentq.gif

Uploaded with ImageShack.us

Homework Equations


w= angular velocity (supposed to be omega)
L= inductor
C= capacitor
j= complex coefficent = sqrt(-1)
Zl= resistance of inductor
Zc= resistance of capacitor
Ztot= total resistance
R= resistance of resistor
P= Power

Xl=wL
Xc=1/wc
Zl=j*Xl
Zc=-j*Xc
Ztot= R + Zl + Zc = R + j(Xl-Xc)



The Attempt at a Solution



with frequency just being high, how am I supposed to get these exact numbers without letters/symbol for I? o.o I tried the calculation and omega did not cancel out either.
 
Last edited by a moderator:
Physics news on Phys.org
The key idea is that in the case of very high or very low frequency, you can take the impedance (resistance) of the inductor and capacitor to be ~infinite, respectively. Does it make sense why that's true (as an approximation at least)?

In effect, this eliminates one of the two loops in the circuit for each case.
 
zhermes said:
The key idea is that in the case of very high or very low frequency, you can take the impedance (resistance) of the inductor and capacitor to be ~infinite, respectively. Does it make sense why that's true (as an approximation at least)?

In effect, this eliminates one of the two loops in the circuit for each case.

ah yes it does, at first I thought the resistance would skyrocket to infinity / 0
thank you
 
Last edited:
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Thread 'Struggle to understand the concept of the question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »

Similar threads

Resonant frequency of L - R||C circuit
Replies
21
Views
1K
Solve AC Voltage Form: RLC Series Circuit Power
Replies
3
Views
7K
Change in Capacitor for largest possible Current
Replies
2
Views
2K
Find the current using jω method
Replies
9
Views
2K
Instantaneous current in a reisistor, capacitor and inductor
Replies
1
Views
2K
RLC Circuit Homework: Find L, Z, I, and P
Replies
8
Views
2K
How Do You Calculate Current and Phase Angle in AC Circuits with Missing Data?
Replies
3
Views
2K
LRC Circuit Problem: Calculate Voltage Across Inductor
Replies
11
Views
3K
Solving for Angular Frequency in Series R to Parallel LC
Replies
23
Views
3K
Power Factor of an L-C-R curcuit
Replies
10
Views
5K

Hot Threads

Recent Insights

Back
Top