MCAT Flashcards

MCAT Flashcards: Ammeters

What are ammeters? Ken Tao is an MCAT expert and explains that an ammeter is a device that is used to measure a current. If you want to measure current passing through a resistor, you need to connect an ammeter in series. Learn more about it in this video!


Full Transcription

In this flashcard video, we’re going to go over ammeters.

An ammeter is a device that is used to measure a current. You can see how ammeters work in this whiteboard drawing. So we have a circuit with a battery, a resistor and an ammeter. If we want to measure the current that is passing through this resistor, we’re going to need to connect an ammeter in series with it as shown in this diagram. The reason why it’s important to connect an amateur in series is because current is the same for circuit elements that are connected in series. This means that whatever current passes through this resistor is also going to pass through the ammeter, and that’s how our ammeter is able to measure the current that passes through that resistor.

Now the ammeter is a circuit element, so it does have internal resistance. An important question to ask is do we want the ammeter to have a high or a low internal resistance? And you can answer that by remembering how resistance works in series. So if you recall resistance adds in series.

So that means that we want to calculate the total resistance of the circuit, it would be equal to the sum of the resistance of the resistor and the internal resistance of the ammeter. So how does this work?

Well, when you have an ammeter, you want it to be able to measure the current passing through the resistor. The addition of the ammeter to the circuit should not affect the circuit. Otherwise, you’re not accurately measuring the current passing through the resistor. So that means if you look at this equation, you want the internal resistance of the ammeter to have the smallest impact possible. And that will happen if you have a very, very small internal resistance. If you look at this equation, if the internal resistance of the ammeter is very small, then the presence or absence of the ammeter is going to have minimal effects on the total resistance of the circuit.

So those are two important things to keep in mind for ammeter. So ammeter are devices used to measure current, and you want to connect them in series in your circuit, and you want them to have a low internal resistance.

Ken Tao

Ken is nationally recognized as a premier MCAT mind. He has worked with thousands of undergraduate students as a graduate teaching assistant and MCAT instructor/tutor for the Princeton Review. At Princeton Review, Ken was the only tutor certified in all subjects, was one of the highest rated MCAT tutors ever and was a teacher trainer. Additionally, Ken worked to found Magoosh's MCAT division. He has written content for dozen's of MCAT books and guides. He is now the Director of MCAT at MedSchoolCoach

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