Current: Average vs. Instantaneous.

In summary, the silver wire with a diameter of 2.6mm transfers a charge of 420 C in 80 minutes. With a silver containing 5.8*10^28 free electrons per cubic meter, the average current can be found using the formula I= Q/t, as there is not enough information to find the instantaneous current. This is because time intervals correspond to average quantities while specific instants correspond to instantaneous quantities.
  • #1
sweetreason
20
0
----
A silver wire 2.6mm in diameter transfers a charge of 420 C in 80min . Silver contains 5.8*10^28 free electrons per cubic meter.

What is the current in the wire?
-----

I have correctly solved this problem using I= Q/t, but I am a bit confused by this. Correct me if I'm wrong, but this is the formula for *average* current. I thought that in general, I= dQ/dt, and that only in cases when you have a complete circuit is the current the same everywhere. In this special case, the average current would be equal to the instantaneous current, but we are not given that we have a complete circuit. So why do we use the formula for average current?

Thanks!
 
Physics news on Phys.org
  • #2
You're not given enough information to find the instantaneous current, so you need to make a simplifying assumption that the current is constant.

Another way of looking at it is that time intervals corresponds to average quantities while particular instants correspond to instantaneous quantities. It generally wouldn't make sense to ask for the average current at t=0 s or for the instantaneous current from t=0 s to t=1 s. It does make sense, on the other hand, to ask for the average of the current over the time interval t=0 s to t=1 s, or to ask for the current at the instant t=0 s. The problem statement gives you a time interval of 80 minutes, so the only current you can find is the average current. If you were supposed to find an instantaneous current, you'd have to be given a particular instant in time for which to find the current.
 

Related to Current: Average vs. Instantaneous.

1. What is the difference between average and instantaneous current?

Average current is the amount of electric charge passing through a given point in a circuit per unit time, while instantaneous current is the measure of the current at a specific moment in time.

2. How is average current calculated?

Average current is calculated by dividing the total amount of charge passing through a point in a circuit by the time it takes for the charge to pass through that point.

3. What is the significance of average current?

Average current is important because it gives us a measure of the overall flow of electric charge in a circuit. It can help us understand the behavior of different components in a circuit and ensure that the circuit is functioning properly.

4. How is instantaneous current measured?

Instantaneous current can be measured using a device called an ammeter, which measures the flow of electric charge at a specific moment in time. This can also be calculated by measuring the voltage across a known resistance in the circuit using Ohm's Law (I = V/R).

5. What factors can affect the average and instantaneous current in a circuit?

The resistance of the components in the circuit, the voltage applied, and the type of circuit (series or parallel) can all affect the average and instantaneous current in a circuit. Changes in any of these factors can cause fluctuations in the current flow.

Similar threads

  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
28
Views
1K
  • Introductory Physics Homework Help
Replies
22
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
10
Views
2K
  • Introductory Physics Homework Help
Replies
8
Views
1K
  • Introductory Physics Homework Help
Replies
6
Views
862
  • Classical Physics
Replies
9
Views
899
  • Introductory Physics Homework Help
Replies
12
Views
2K
Back
Top