Tasks

1. Learn to measure current in a circuit using a multimeter.
2. Measure the current and voltage through a single resistor when connected in series with a battery.
3. Build the two simple circuits below with a battery and three resistors, predict the currents at each numbered point and the voltage drops across each resistor, and verify they are correct using a multimeter.

Resources

• Multimeter
  • Video tutorial: measuring current
• Resistors
• Battery
• Wires with alligator clips

Background

An electrical circuit is a series of wires and components that are connected in a way that forms one or more closed paths for electrons to follow. Current is the amount of charge per second passing through a given  point in the circuit. Voltage is the energy required for charges to move from one point in the circuit to another, and is affected by things such as batteries and the resistance of various components.

Most electrical circuits perform functions by turning the current on and off, for example a switch turning on a light, or a digital circuit sending information as a series of ones and zeroes. A circuit made out of a battery and a few resistors doesn’t do much, but it is useful for understanding the basic relationships between current and voltage in a circuit using three simple rules:

• Kirchoff’s Junction Rule: The sum of the currents entering any point or junction in a circuit must be equal to the sum of the currents leaving.
• Kirchoff’s Loop Rule: The changes in voltage around any closed loop in a circuit must add up to zero.
• Ohm’s Law: The voltage between two points in a circuit is equal to the resistance times the current: V=IR