1. Electrical resistance Resistance measures how difficult it is for current to flow.

2. Electrical Resistance The total amount of electrical resistance in a circuit determines the amount of current that in the circuit for a given voltage. The more resistance the circuit has, the less current that flows.

3. Measuring resistance Set the meter to measure resistance (  ). Set the black and red leads on opposite ends of the objects.

4. The ohm Resistance is measured in ohms (  ). One ohm is the resistance when a voltage of 1 volt is applied with a current of 1 amp.

5. Ohm's law German physicist Georg Ohm experimented with circuits to find an exact mathematical relationship between voltage, current and resistance. Ohm's law can be used to predict any one of the three variable if given the other two.

7. Calculate current A light bulb with a resistance of 2 ohms is connected in a circuit that has a single 1.5- volt battery. Calculate the current that flows in the circuit. Assume the wires have zero resistance.

8. The resistance of electrical devices The resistance of electrical devices ranges from very small (0.001 Ω) to very large (10×10 6 Ω). Each device is designed with a resistance that allows the right amount of current to flow when connected to the voltage the device was designed for.

9. Changing resistance The resistance of many materials, including those in light bulbs, increases as temperature increases. A graph of current versus voltage for a light bulb shows a curve. A device with constant resistance would show a straight line on this graph.

10. Electrical Conductivity The electrical conductivity describes a material’s ability to pass electric current.

11. 19.3 Conductors and insulators A material such as copper is called a conductor because it can conduct, or carry, electric current. Materials that insulate against (or block) the flow of current are classified as electrical insulators. Some materials are neither conductors nor insulators. These materials are named semiconductors.

12. 19.3 Resistors Electrical components called resistors can be used to control current. Resistors have striped color codes to record their "values" (writing on them is difficult).