An ammeter is an instrument that shows how much current passes through it. It is

Question

An ammeter is an instrument that shows how much current passes through it. It is designed to have a small resistance. The following problems show why.

A. Suppose an ammeter having a resistance of 0.5 ? is connected in parallel across a resistor of 50.0 ? as shown in the figure at the bottom.

- If the system is connected up to a 12 V battery, how much current would pass through the ammeter (Assume you can ignore the internal resistance of the battery.)

- How much current would pass through the 50 ohm resistor? Is this ammeter giving a good measure of the current in the 50 ohm resistor? Explain why or why not.

- Is this ammeter giving a good measurement of what the current would be in the resistor if the ammeter weren't there?

Explanation / Answer

in parallel Reff = r1r2/r1+r2 = 50*0.5/50.5 Reff = 0.495 0hms current i = v/Reff = 12/0.495 = 24.24 amps through ammter across resistance of 50 ohm, current i = 12/50 = 0.24 amps. yes it is giving a very high vaue of current, in parallel combintion,net effective resistance decreases so that high currents can be seen. hence parallel combination is preferred. in the absence of ammerter , a current of 0.24 amps would be passing, addition of just 0.5 ohms in parallel made a lot of difference.

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