- 1). Set the power supply on the table. Make sure an outlet is close by. Place the light bulb in the light bulb holder. Cut two 12 inch pieces of black wire. Strip 1/2 of an inch of insulation off of the ends of each wire.
- 2). Connect the negative terminal of the power supply to one of the two terminals on the light bulb socket using one of the two black wires. Connect one end of the second black wire to the second terminal of the light bulb socket.
- 3). Connect the other end of the second black wire to the black negative wire from the digital multimeter. Connect the red probe wire from the digital multimeter to the positive terminal of the power supply.
- 4). Set the digital multimeter to measure current in amps. This setting is usually indicated by "10A." Turn the multimeter on and plug in the power supply. Turn the power supply on and increase the power supply voltage to 12 volts. Write down both the 12 volt voltage reading and the current reading shown on the digital multimeter. If the current reading is 1.5 amps, write that down, for example.
- 5). Multiply the voltage and current readings. For example, 12 volts times 1.5 amps equals 18 watts. This is the amount of power that the light bulb is using.
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