How much current (in A) flows through the ammeter for Circuit b?

[kapopka88]

The manufacturer of a 12V car headlight specifies it will draw a current of 6A. You would like to check this claim with an ammeter designed to measure currents up to 10A and having a resistance of 0.1 Ohms. Which of the two figures below represents a circuit where the ammeter correctly measures the current in the headlight?
OA-Ammeter.bmp

a. Circuit a.
b. Circuit b.

How much current (in A) would flow in the ammeter for Circuit a?

i thought A would equal V/R, which in this case i thought would be 12/.1= 120 amps... but this is not correct. please help!

How much current (in A) flows through the ammeter for Circuit b?

 

[jhicks]

The pictures haven't authenticated yet, but ammeters are used in series with the load (headlight) so that the combined resistance of the circuit is 0.1ohm + the resistance of the headlight which is supposedly 12V/6A = 2ohm. If the headlight truly is 2ohm, you should see slightly less current than 6A with the ammeter hooked up (it's your job to find how much though).

 

[Moetasim]

For Circuit b, the current flowing through the ammeter can be calculated using Ohm's law: I = V/R, where I is the current, V is the voltage, and R is the resistance.

In this case, the voltage (V) is 12V and the resistance (R) is 0.1 Ohms. Therefore, the current flowing through the ammeter for Circuit b would be:

I = 12V / 0.1 Ohms = 120 amps

This means that the ammeter would correctly measure the current in the headlight, since the manufacturer specified it would draw a current of 6A and the ammeter is capable of measuring currents up to 10A. The figure for Circuit b is the correct one.

For Circuit a, the current flowing through the ammeter would be:

I = 12V / 0.1 Ohms = 120 amps

This is also correct, but it does not match the manufacturer's specification of 6A for the headlight. Therefore, the figure for Circuit b is the correct one for measuring the current in the headlight.