Question Video: Identifying The Connection of Ammeters in Circuits | Nagwa Question Video: Identifying The Connection of Ammeters in Circuits | Nagwa

# Question Video: Identifying The Connection of Ammeters in Circuits Science • Third Year of Preparatory School

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Each of the following diagrams shows a circuit containing a cell, a bulb, and an ammeter. Which one shows how the ammeter must be connected to the circuit in order to measure the current in the circuit?

03:39

### Video Transcript

Each of the following diagrams shows a circuit containing a cell, a bulb, and an ammeter. Which one shows how the ammeter must be connected to the circuit in order to measure the current in the circuit?

Okay, so in order to answer this question, we should first recall that an ammeter is in fact used to measure the current in a circuit. However, it has to be connected in a very specific way into the circuit in order for it to work. We’ve been told that each one of these circuit diagrams (A), (B), (C), and (D) shows us a cell, a bulb, and an ammeter. Let’s recall that the circuit symbol of a cell looks like this, a short line to represent the negative terminal of the cell and a long line to represent the positive terminal. A bulb is drawn like this, a circle with a cross through it. And an ammeter is drawn this way, a circle with a capital A inside it. And we can see that each one of these circuit diagrams does, in fact, have a cell, a bulb, and an ammeter in it.

Now, let’s also recall that for an ammeter to work, it must be connected in series in our circuit. So let’s go through each circuit and see if our ammeter is indeed connected in series. Let’s start with circuit (A). We can imagine charges flowing from the positive terminal of our cell. In other words, we’re considering the current in our circuit. And in this particular case, as soon as we get to this junction, some of the charges must be going off in this direction, whereas the others go off in this direction. And then we see the ammeter connected on one of these branches. Therefore, we can say that our ammeter is not connected in series in this circuit.

An additional problem is that the circuit is not even complete. We can see that the end of this wire here is not connected to anything; it’s just sort of left there. Therefore, we can definitively say that circuit (A) is not the correct way in which to connect an ammeter in order to measure the current in our circuit.

Moving on to circuit (B) then, we can once again begin at the positive terminal of our cell and consider the charges flowing in this direction. We can see that all of the current does indeed pass through our ammeter and then through the bulb before continuing clockwise and arriving at the negative terminal of the cell. At which point we’ve gone around the entire circuit and all of the current has passed through our ammeter. It is connected in series. Therefore, option (B) is a good candidate for a correct circuit.

Moving on to option (C) though, we can once again begin at the positive terminal of the cell, going this way clockwise. Then we can see that all of the current does pass through the bulb. But as soon as we get to this junction here, the current must split. Some goes in this direction and the rest in this direction. And then we see that the ammeter is again on one of these branches. Additionally, we’ve got the same problem as in circuit (A). The circuit is actually incomplete. This end of the wire is not connected to anything. So because our ammeter is not connected properly in circuit (C) and it’s also an incomplete circuit, we can say that this is not a correct answer.

Finally, moving on to circuit (D) again, beginning at the positive terminal, we go around clockwise until we get to this junction here. Now, at this point, we may have been able to say that our ammeter was at least connected in parallel if the circuit had been completed, for example, if we had a wire that looked like this dotted line. And in that case at least, the ammeter would have been connected in parallel with our circuit, and the circuit would have been a complete circuit. That still wouldn’t mean that the ammeter was functioning because again it needs to be connected in series. And in fact, for the given circuit, neither is the ammeter in series nor is the circuit complete. So, option (D) is out of the question as well. At which point we can say that option (B) shows us how to correctly connect an ammeter in order to measure the current in a circuit.

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