Measuring Electric Current and Voltage

D Battery

Electricity results from the movement of charged particles along a path called a circuit. Electric current, the rate at which charges move along a conductor, is measured in units called amperes, or amps. The amount of current in a conductor can be measured with an ammeter.

Just like a rock poised at the top of a hill, electrical charges can have potential energy, the energy of position. The difference in the potential energy between two points along a conductor is referred to as the voltage of the current. Even though it is not actually a force, voltage can be thought of as the driving force behind an electrical current. Voltage, which is measured in volts, can be read with a voltmeter. Devices such as batteries provide voltage.

A circuit must be closed for an electric current to travel along it. Circuits can be opened by switches, which are important components of most appliances. When an appliance is turned off, the switch is open and electricity cannot travel through the circuit. Closing the switch completes the circuit and allows electricity to flow.

In this experiment, you will measure the current and voltage of an electrical circuit.

  • bulbs
  • D batteries
  • 500-mA ammeter
  • digital voltmeter
  • bulb holders
  • 2 to 4 wires with alligator clips
  • data table
  1. Screw a lightbulb into a bulb holder. Click on the alligator clips to attach the bulb holder. These clips are used to make connections to the bulb.
  2. Close the switch and notice the brightness of the bulb.
  3. Add a second D battery to the battery holder. Attach the alligator clips to the battery. Close the switch and observe any change to the brightness of the bulb.
  4. An ammeter can be used to find out how much the amount of current in the circuit changed when a battery was added to it. Open the switch and insert the ammeter, between the battery and the switch.
  5. The ammeter is calibrated in milliamps (mA). Close the circuit, and record in your data table the amount of current flowing through the circuit when two batteries are in the battery holder.
  6. Open the switch and remove one of the batteries. Close the switch to determine how much current is flowing through the circuit. Record your findings in your data table.
  7. Attach the voltmeter to the light holder using alligator clips.
  8. Open the switch. Attach one more bulb between the light bulb and the battery using alligator clips. Set up the voltmeter to measure the current across both bulbs. Record you findings in data table.
  1. How did adding a battery to the circuit in step 3 change the brightness of the lightbulb?
  2. Did adding a battery increase or decrease the amount of current flowing through the circuit? How do you know?
  3. A D battery has a voltage rating of 1.5. How did your reading with the voltmeter compare?
  4. What is the voltage drop across one bulb? What is the voltage drop across two bulbs?
  1. Adding a battery increased the brightness of the bulb.
  2. Adding a battery increased the amount of current in the wire. The brightness of the bulb varies with the amount of current, and the ammeter reading increased.
  3. Answers will vary, but will be less than 1.5 volts.
  4. Answers will vary, but the voltage drop for one or two bulbs will be less than 1.5 volts.
Data Table
Data Table
Magnetic Field Direction Compass Behaviour