How to measure Current, Voltage and Resistance

Understanding Electricity

How to measure current

The instrument used to measure current is called ampere meter or ammeter.

• Steps for current measurement Connect a small light bulb to a dry cell. Measure current that passes through light bulb by connecting positive terminal (+) of the ammeter to negative terminal (-) of a dry cell (see figure)

• Safety instructions for current measurement;
1. Estimate current that required measuring then choose a suitable ammeter, since each ammeter has the different limit of current measurement.
2. Be sure that the connection to a positive terminal (+) and the negative terminal (-) of ammeter are correct.
3. Do not directly connect ammeter terminals to dry cell terminals. Since it can damage the meter.

How to measure the voltage

The instrument used to measure voltage, difference potential or electromotive force is called voltmeter.

• Steps for voltage measurement

Connect a small light bulb to a dry cell. A voltmeter is wired in parallel with the light bulb to measure the voltage across the light bulb. Connect positive terminal (+) of the voltmeter to positive terminal (+) of a dry cell and connect negative terminal (-) of the voltmeter to negative terminal (-) of a dry cell (see figure).

• Safety instructions for measuring voltage;
1. Estimate voltage that required measuring then choose a suitable voltmeter, since each voltmeter is designed with the limit of voltage measurement.
1. Be sure that the connecting of positive terminal (+) and the negative terminal (-) of the voltmeter are correct.

How to measure resistance

The instrument used to measure resistance is called test meter or multimeter. The multimeter or test meter is used to make various electrical measurements such as current, voltage and resistance. It combines the functions of ammeter, voltmeter and ohmmeter.

• Steps for resistance measurement
• Turn the face dial to a position for required measuring, resistance, then touch both of terminals of multimeter (see figure 1) and adjust the meter range to 0 Ω. Touch both of terminals of the meter to a resistance and take the reading (see figure 2).