15 - MULTITESTER: THE AMMETER AND THE VOLTMETER

Question 1

A ____________ is a very useful device capable of measuring current and voltages. This instrument utilizes the ___________ principle and involves the concept of electric current, voltage and resistance.

Answer 1

multitester
galvanometer principle

Question 2

When used as an _________, the multitester should be connected in series with the circuit.

Answer 2

ammeter

Question 3

as an Ammeter

1. Connect the ____ test lead to the positive terminal and the ______ test lead to the negative terminal of the multitester.
2. Set the function switch to _______ and the range switch to _______ (the maximum current that the meter can measure).
3. Open the circuit at the point where the current is to be measured and securely connect the test leads in series with the load. Connect the _________ source. _______ should be noted in DC current measurements.
4. Do not touch _________ of test leads.
5. Set the selector switch to DCA function. Each of the four range notations (50 MA-0.25A) indicates the _________ current reading for that range. The scale reading for _____ line read 0-0.25 A, 0-25 mA and 0-2.5 mA, while ______ is read on 0-50 line. As a safety measure, start from the highest range.
   Close the switch and measure the current in the circuit for different ranges starting from the highest range. Record your data in Table 15.1 (Note: Do not try to get a reading if the reading exceeds the range)
6. Open the switch and disconnect the power source.

Answer 3

1. red, black
2. DCA, 0.25A
3. 6V DC , Polarity
4. uninsulated tips
5. maximum, 0-250 line, 0-50 µA

Question 4

At what range will the current in the resistor be accurately measured?

Answer 4

range closest to the actual current value

Question 5

If the ammeter is connected in parallel to a circuit component, what do you think will happen?

Answer 5

the ammeter has very low internal resistance which may cause4 short circuit and potentially high current flow damaging the ammeter

Question 6

If no deflection occurs when measuring current, what does this indicate?

Answer 6

no current flowing or the circuit is open

Question 7

How would you increase the accuracy of the current measurements?

Answer 7

Select an ammeter range close to the expected current value.

Ensure the ammeter is properly calibrated before use. Calibration ensures the meter’s readings are accurate and consistent.

Question 8

B. The Multitester as a Voltmeter

1. Connect the voltmeter in _______ to the component being measured. Switch the range to its maximum setting for unknown voltages to be measured. ______ should be noted in DC voltage measurements. The positive test lead should be connected to the positive terminal and the negative lead to the negative terminal with respect to the polarity of the voltage source.
2. Set the function switch to the desired ________ position.
3. Set the selector switch knob of the meter to DCV function and connect it in _________ with the resistor. The scale reading for 0-10V, 0-50V and 0-250V are read from 0-10, 0-50 and 0-250 lines respectively.
4. Close the switch. Measure the voltage across R. Start from the largest range.
5. Record all your data in Table 15.2.

Answer 8

1. parallel, Polarity
2. DCV
3. parallel

Question 9

1. Why must voltmeters be connected in parallel with the circuit component?

Answer 9

Voltage measures the difference in electric potential between two points.
To find this difference across a component, the voltmeter must connect to both ends (or terminals) of the component, which is achieved by connecting it in parallel.

Voltmeters must be connected in parallel to correctly measure the potential difference across a component without altering the circuit’s operation.

When connected in parallel, the voltmeter doesn’t significantly alter the behavior of the circuit or the voltage it is measuring.

Question 10

2. What are the possible effects on the voltmeter if voltages to be measured exceed the range?

Answer 10

the needle will stay at the far left (infinity mark), indicating the resistance is too high. This happens because the meter’s internal current cannot flow through such a large resistance, and no damage typically occurs.

Question 11

3. For this experiment, the needle seems undeflected when the range was 0-1000 V. Why?

Answer 11

because the voltage being measured is too low compared to the meter’s high range setting. Voltmeters have different sensitivity based on the selected range, and in a high-range setting (like 1000 V), even a relatively small voltage may not cause the needle to move significantly, as the scale is less sensitive at higher voltage ranges.