In reality, we cannot always rely on circuit diagrams to get an accurate representation of the values that go into our circuits. We use devices to help determine the magnitude of current, voltage, and resistance. These devices known as โmetersโ help in monitoring parameters to make sure that a circuit works well and isnโt prone to damage. Having meters to use in circuits allows us to ensure safety and be more confident about the power output that our circuit puts out. While having meters set in a circuit sounds straightforward, using devices on circuits comes with challenges. One of which is making sure that they do not add or influence the parameters being measured. Letโs take another look at the three meters weโve previously discussed.
I. Ammeter
An Ammeter is used to measure current. The way to remember this is by thinking that weโre using an โAmpโ-meter which corresponds to amperesโthe unit measure for electric current. Since electric current tells us the flow rate of charges, we need to connect the ammeter along the path of the current or in series. An ammeter must be connected in series so the current can flow directly through the ammeter. Ammeters ideally have minimal to no resistance since we do not want the instrument to influence a voltage drop and make an inaccurate measurement.
II. Voltmeter
Voltmeters measure the voltage or the potential difference between two points in a circuit. Since potential difference tells us how much work is needed to move a charge from one point to another, voltmeters are typically placed in between batteries and resistors since these components cause a voltage drop in a circuit. Unlike ammeters, voltmeters must be placed parallel to the component and not in series since the device will only be concerned with the difference between two points. Voltmeters have a high resistance to minimize the current they draw from the circuit.
III. Ohmmeter
An Ohmmeter measures the resistance of a component or a circuit. Resistance is the measure of how much a component resists current flow. We can remember ohmmeters by thinking that ohmmeters measure ohms which is the unit measure for resistance. Unlike ammeters and voltmeters, ohmmeters must be used on an isolated component . Since there is no current flow, ohmmeters do not influence whatever happens once the circuit is connected to a power source. Ohmmeters measure a componentโs resistance while itโs disconnected from the power source. They have positive and negative terminals and can be directly used by turning on the device and touching both ends of the probes on the positive and negative ends of the component that we want to measure.
IV. Conclusion
Circuits require instruments to measure certain values that cannot always be determined using formulas. These instruments can measure the flux of flow or the magnitude of damage in the component itself which is something that numbers canโt always be accurate about. Itโs good to have background knowledge on how we apply theoretical knowledge in the real world. These meters are essential in maintaining components and having a proper benchmark on how close we can get to the numbers we can calculate theoretically.
V. Key Terms
- Ammeter - a meter used to measure the current across a circuit.
- Ohmmeter - a meter used to measure the resistance of a component.
- Probe - a component of a meter used to connect the meter to a component or circuit.
- Voltmeter - a meter used to measure voltage
VI. Practice Questions
Sample Practice Question 1
The following accurately describes meters used in circuits EXCEPT:
A. Ammeters are connected in between the load and the power source to measure the current.
B. Voltmeters can measure the potential difference between the positive and negative terminals of the battery.
C. An ohmmeter measures the resistance of a component in an open circuit.
D. Voltmeters are connected in parallel to measure the voltage of an open circuit.
Ans. D
Sample Practice Question 2
Determine which circuit is not connected correctly.
A. Circuit 1
B. Circuit 2
C. Circuit 3
D. Circuit 4
Ans. B
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