Ammeter
Ammeter
An ammeter is an instrument used to measure the rate of flow of electric current in a circuit. Since one is interested in measuring the current flowing through a circuit component, the ammeter must be connected in series with the measured circuit component.
Ammeter
Optional Activity: Constructing Circuits
Construct circuits to measure the emf and the terminal potential difference for a battery. Some common elements (components) which can be found in electrical circuits include light bulbs, batteries, connecting leads, switches, resistors, voltmeters and ammeters. You have learnt about many of these already. Below is a table with the items and their symbols:
|
Component |
Symbol |
Usage |
|
light bulb |
glows when charge moves through it |
|
|
battery |
provides energy for charge to move |
|
|
switch |
allows a circuit to be open or closed |
|
|
resistor |
resists the flow of charge |
|
|
OR |
||
|
voltmeter |
measures potential difference |
|
|
ammeter |
measures current in a circuit |
|
|
connecting lead |
connects circuit elements together |
Experiment with different combinations of components in the circuits.
The table below summarises the use of each measuring instrument that we discussed and the way it should be connected to a circuit component.
Tip:
A battery does not produce the same amount of current no matter what is connected to it. While the voltage produced by a battery is constant, the amount of current supplied depends on what is in the circuit.
|
Instrument |
Measured Quantity |
Proper Connection |
|
Voltmeter |
Voltage |
In Parallel |
|
Ammeter |
Current |
In Series |
Optional Activity: Using Meters
If possible, connect meters in circuits to get used to the use of meters to measure electrical quantities. If the meters have more than one scale, always connect to the first so that the meter will not be damaged by having to measure values that exceed its limits.
Example: Calculating Current I
Question
An amount of charge equal to \(\text{45}\) \(\text{C}\) moves past a point in a circuit in \(\text{1}\) \(\text{second}\), what is the current in the circuit?
Step 1: Analyze the question
We are given an amount of charge and a time and asked to calculate the current. We know that current is the rate at which charge moves past a fixed point in a circuit so we have all the information we need. We have quantities in the correct units already.
Step 2: Apply the principles
We know that:
\begin{align*} I & = \frac{Q}{\Delta t} \\ I & = \frac{\text{45}\text{ C}}{\text{1}\text{ s}} \\ I & = \text{45}\text{ C·s$^{-1}$} \\ I & = \text{45}\text{ A} \end{align*}Step 3: Quote the final result
The current is \(\text{45}\) \(\text{A}\).
Example: Calculating Current II
Question
An amount of charge equal to \(\text{53}\) \(\text{C}\) moves past a fixed point in a circuit in \(\text{2}\) \(\text{s}\), what is the current in the circuit?
Step 1: Analyze the question
We are given an amount of charge and a time and asked to calculate the current. We know that current is the rate at which charge moves past a fixed point in a circuit so we have all the information we need. We have quantities in the correct units already.
Step 2: Apply the principles
We know that:
\begin{align*} I & = \frac{Q}{\Delta t} \\ I & = \frac{\text{53}\text{ C}}{\text{2}\text{ s}} \\ I & = \text{26.5}\text{ C·s$^{-1}$} \\ I & = \text{26.5}\text{ A} \end{align*}Step 3: Quote the final result
The current is \(\text{26.5}\) \(\text{A}\).
Example: Calculating Current III
Question
95 electrons move past a fixed point in a circuit in one tenth of a second, what is the current in the circuit?
Step 1: Analyze the question
We are given a number of charged particles that move past a fixed point and the time that it takes. We know that current is the rate at which charge moves past a fixed point in a circuit so we have to determine the charge. In the last section we learnt that the charge carried by an electron is \(\text{1.6} \times \text{10}^{-\text{19}}\) \(\text{C}\).
Step 2: Apply the principles: determine the charge
We know that each electron carries a charge of \(\text{1.6} \times \text{10}^{-\text{19}}\) \(\text{C}\), therefore the total charge is:
\begin{align*} Q& = 95 \times \text{1.6} \times \text{10}^{-\text{19}}\text{ C} \\ & = \text{1.52} \times \text{10}^{-\text{17}}\text{ C} \end{align*}Step 3: Apply the principles: determine the charge
We know that:
\begin{align*} I & = \frac{Q}{\Delta t} \\ I & = \frac{\text{1.52} \times \text{10}^{-\text{17}}\text{ C}}{\frac{1}{10} \text{ s}} \\ I & = \frac{\text{1.52} \times \text{10}^{-\text{17}}\text{ C}}{1} \times \frac{1}{\frac{1}{10} \text{ s}} \\ I & = \frac{\text{1.52} \times \text{10}^{-\text{17}}\text{ C}}{1}\times \frac{10}{\text{1}\text{ s}} \\ I & = \text{1.52} \times \text{10}^{-\text{16}}\text{ C·s$^{-1}$} \\ I & = \text{1.52} \times \text{10}^{-\text{16}}\text{ A} \end{align*}Step 4: Quote the final result
The current is \(\text{1.52} \times \text{10}^{-\text{16}}\) \(\text{A}\).
This lesson is part of:
Electric Circuits