Why multimeter connected in series

It is connected in parallel to the circuit element so that all the voltage is dropped across it and it can measure the voltage. So by connecting it in series, we will be reducing the current to nearly zero. On other words it will lead to an open circuit. Therefore care must be taken while measuring voltage using multimeter. It must be ensured that multimeter is selected in voltage mode before measuring voltage between two points.

If by mistake, multimeter is selected in current mode and we measure the voltage between two points, this simply means we are connecting ammeter in parallel which means high current through the meter as well as circuit. A potentiometer is a null measurement device for measuring potentials voltages. A voltage source is connected to resistor R, passing a constant current through it.

There is a steady drop in potential IR drop along the wire, so a variable potential is obtained through contact along the wire. An unknown emf x represented by script E x connected in series with a galvanometer is shown in. Note that emf x opposes the other voltage source. The location of the contact point is adjusted until the galvanometer reads zero. Since no current flows through the galvanometer, none flows through the unknown EMF, and emf x is sensed.

Potentiometer : The potentiometer is a null measurement device. A voltage source connected to a long wire resistor passes a constant current I through it. An unknown EMF labeled script Ex is connected as shown, and the point of contact along R is adjusted until the galvanometer reads zero.

The unknown EMF is thus proportional to the resistance of the wire segment. In both cases, no current passes through the galvanometer. The current I through the long wire is identical. The three quantities on the right-hand side of the equation are now known or measured, and emf x can be calculated. There is often less uncertainty in this calculation than when using a voltmeter directly, but it is not zero. Furthermore, it is not possible to tell when the galvanometer reads exactly zero, which introduces error into both R x and R s , and may also affect the current I.

Many so-called ohmmeters measure resistance. Their readout is this calculated resistance. Simple configurations using standard voltmeters and ammeters have limited accuracy, because the meters alter both the voltage applied to the resistor and the current flowing through it.

The Wheatstone bridge is a null measurement device for calculating resistance by balancing potential drops in a circuit. The device is called a bridge because the galvanometer forms a bridge between two branches. A variety of bridge devicesare used to make null measurements in circuits. Resistors R 1 and R 2 are precisely known, while the arrow through R 3 indicates that it is a variable resistance.

The value of R 3 can be precisely read. With the unknown resistance Rx in the circuit, R 3 is adjusted until the galvanometer reads zero. Wheatstone Bridge : The Wheatstone bridge is used to calculate unknown resistances. The variable resistance R3 is adjusted until the galvanometer reads zero with the switch closed. This simplifies the circuit, allowing Rx to be calculated based on the IR drops.

The potential difference between points b and d is then zero, meaning that b and d are at the same potential. With no current running through the galvanometer, it has no effect on the rest of the circuit.

So the branches abc and adc are in parallel, and each branch has the full voltage of the source. Since b and d are at the same potential, the IR drop along ad must equal the IR drop along ab. Again, since b and d are at the same potential, the IR drop along dc must equal the IR drop along bc.

This equation is used to calculate the unknown resistance when current through the galvanometer is zero. This method can be very accurate, but it is limited by two factors. This tutorial from SparkFun provides directions for changing a fuse on their brand of multimeter, but remember that these directions might not apply to your model. Note that in some multimeters-especially in inexpensive ones-you might not be able to change the fuse. In this multimeter tutorial, we have already covered what a multimeter is and how to use it.

This section will provide some suggestions of practical and interesting things to do with a multimeter. Remember that the primary purpose of a multimeter is to test circuits and electrical components in an experiment or science project that involves electronics. What if you don't have a circuit to test? Here are a couple suggestions for quick experiments you can do with a multimeter around your house. A lot of Science Buddies projects require a multimeter; it is a really handy tool!

In fact, there are too many to list, but here is a sampling of a few that cover a variety of topics:. While most multimeters can perform the same basic functions, different models that are made by different manufacturers might not all look the same. In the gallery below, we have provided a series of images of different multimeters with different measurement settings and sockets for the probes labeled.

Note that most of the multimeters have basic features in common, including settings for measuring voltage, current, and resistance. All of them have a single "ground" socket for the black probe. Most of them have separate sockets for measuring high and low current. The low-current socket is also used to measure voltage and resistance. However, some multimeters only have two sockets total, or only have one socket for measuring current.

Some also have additional features that we did not label. Remember, this gallery is meant to be a general guide; if you do not see your model of multimeter pictured here, your best bet is to consult your specific multimeter's manual. If you need help getting introduced to multimeters in general, refer back to our Multimeter Overview section. If you need to know how to take a specific type of measurement, refer to the Using a Multimeter section.

If you have read through this multimeter tutorial and still have unanswered questions, the references below might be helpful. Menu Science Projects. Project Guides. View Site Map. Science Projects. Grade Levels. Physical Science. Earth and Environmental Science. Behavioral and Social Science. How to Use a Multimeter. Figure 1. A typical multimeter. Technical Note The symbol that is used for a unit is usually different than the symbol for a variable in an equation. For example, voltage, current, and resistance are related by Ohm's law see the References tab to learn more about Ohm's law : [Please enable JavaScript to view equation] which is usually expressed as [Please enable JavaScript to view equation] In this equation, V represents voltage, I represents current, and R represents resistance.

Figure 2. In a basic series circuit left , each element has the same current but not necessarily the same voltage; that will only happen if their resistances are all the same. In a basic parallel circuit right , each element has the same voltage but not necessarily the same current; that will only happen if their resistances are all the same.

Figure 3. The multimeter on the left is manual-ranging, with many different options indicated by metric prefixes for measuring different amounts of voltage, current, and resistance.

The multimeter on the right is auto-ranging note how it has fewer options for the selection knob , meaning it will automatically select the appropriate range. This stands for alternating current AC. Note that the voltage in an AC circuit is usually referred to as "AC voltage" even though it sounds strange to say "alternating current voltage". You use these settings when you are measuring a circuit with alternating current or voltage. The straight lines stand for direct current. You use these settings when you are measuring a circuit with direct current e.

Continuity check series of parallel arcs : This is a setting used to check if two things are electrically connected. The multimeter will beep if there is a conductive path between the two probe tips meaning, if the resistance is very close to zero , and will not make any noise if there is no conductive path. Note that sometimes the continuity check can be combined with other functions on a single setting. Diode check triangle with some lines through it : This function is used to test a diode , which is like a one-way valve for electricity; it only lets current flow in one direction.

The exact function of the diode check can be different on different multimeters. Check your multimeter's manual to learn about how the diode check function works for your model.

Table 1. Some symbol examples from different multimeters. Check out the gallery for more examples. Figure 4. A typical pair of multimeter probes. Figure 5. This section includes answers to the following questions: How do I measure voltage?

How do I measure current? How do I measure resistance? How do I do a continuity check? How do I do a diode check?

How do I know which scale to pick for voltage, current, or resistance, and how do I read the numbers at different scales? My multimeter isn't working! What's wrong? How do I know if I need to change the fuse? How do I change the fuse? How do I measure voltage? To measure voltage, follow these steps: Plug your black and red probes into the appropriate sockets also referred to as "ports" on your multimeter.

For most multimeters, the black probe should be plugged into the socket labeled "COM," and the red probe into the socket labeled with a "V" it might also have some other symbols. Remember to check out our image gallery, the Multimeter Overview tab, or your multimeter's manual if you have trouble identifying the right socket.

Choose the appropriate voltage setting on your multimeter's dial. Remember that most battery-powered circuits will have direct current, but the setting you select will depend on the science project you are doing.

If you are working with a manual-ranging multimeter, you can estimate the range you need based on the battery or batteries powering your circuit. For example, if your circuit is powered by a single 9V battery, it probably doesn't make sense to select the setting for V, and 2V would be too low.

If available, you would want to select 20V. Touch the probe tips to your circuit in parallel with the element you want to measure voltage across refer to the Multimeter Overview tab for an explanation of series and parallel circuits.

For example, Figure 6 shows how to measure the voltage drop across a lightbulb powered by the battery. Be sure to use the red probe on the side connected to the positive battery terminal, and the black probe on the side connected to the negative battery terminal nothing will be harmed if you get this backwards, but your voltage reading will be negative. Figure 6. Measuring voltage across a lightbulb by attaching the multimeter probes in parallel. Current flow is represented by the yellow arrows.

In voltage-measurement mode, the multimeter's resistance is very high , so almost all of the current flows through the lightbulb, and the multimeter does not have a big impact on the circuit. Figure 7. Measuring the current through a lightbulb by attaching a multimeter in series.

In current-measurement mode, the multimeter's resistance is very low , so the current can easily flow through the multimeter without affecting the rest of the circuit. Notice how the knob has been set to measure direct current DCA and the red probe is plugged into the port for measuring current, labeled with an "A. Figure 8. Measuring the resistance of a lightbulb using a multimeter.

Notice how the lightbulb has been disconnected from the circuit. The multimeter supplies its own small amount of current, which allows it to measure the resistance. Figure 9. Using a multimeter to do a continuity test. If a conductive path is formed between the probe tips, the multimeter will beep. If the conductive path is broken possibly due to a wire that has come loose in your circuit, or a bad solder connection , the multimeter will not beep. Readings when measuring voltage of a single AA battery using different dial settings on a manual-ranging multimeter.

Figure A typical fuse. This section answers the questions: What can I do with a multimeter around the house? What shouldn't I do with my multimeter? Which Science Buddies projects require a multimeter? What can I do with a multimeter around the house? Test batteries! Have you ever wondered if a device or toy stopped working because the batteries were dead?