Circuits, Volts, Amps, and Resistance

Series circuits Simple circuits that have only one path for the current to flow are called series circuits.

Series circuits can be compared to that of a race track.

Parallel Circuits Parallel circuits are circuits that allow electricity to flow in multiple paths.

Parallel circuits are more like city streets than a race track. They give the electricity options for movement.

The Battery Batteries contain stored electric potential energy from chemical reactions that go on inside the battery. A good example of the reaction is: Zn + Cu 2+ = Zn 2+ + Cu

The battery provides the potential energy to do “work” In order to do this “work” the battery must be connected in a closed circuit

Energy is measured in “Joules” The energy that is stored in the battery is also measured in Joules. Potential energy difference is measured in Joules per Coulomb or Volts.

Therefore: V = E QSo Potential energy difference = the amount of stored energy charge charge

We can measure potential energy difference using a voltmeter. The measure is in volts. V

The voltmeter must be put in parallel with the circuit. This means it must create it’s own separate loop in the circuit to work properly.

The voltmeter will measure the difference at one point on the circuit and compares it to another point on the circuit.

The Ammeter An ammeter measures current through the circuit. It measures amps Think about current as the speed that the charges travel, an ammeter is like a speed radar gun for electricity. A

An ammeter must be put in series to work properly.

Resistance What does it mean to “resist”? What would be harder? 1.Pushing a 50kg box across carpet? 2.Pushing a 50kg box across tile floors?

Resistance is the property of a substance to hinder motion. A resistor converts electric energy into other forms of energy (heat, light)

Resistance is the ratio of potential energy difference (voltage) across a load, to the current through the load Resistance = Voltage Current Current Resistance is measured in Ohms or Ω

Ohm’s Law This equation is referred to as Ohm’s Law Where V = IR V IR

If we had a voltmeter and a ammeter we could measure the resistance

Example Question What is the resistance of the heating coil of an electric heater, if a current of 12.5A runs through it, when connected to a wall outlet of 120V? Given:Solution:Paraphrase:

Example Question What is potential difference (voltage) across a light bulb that has a resistance of 3ohms and a current of 1.5A Given:Solution:Paraphrase:

Factors that effect resistance 1.Length – resistance increases with length 2.Cross sectional area – resistance decreases when area increases 3.Temperature – resistance increases when temperature decreases 4.Material – some metals allow electrons to move more freely than others

Page 342 #1-6 1.In your own words explain electrical resistance. 2.What is the formula for resistance and what units are equivalent to the ohm? 3.List 3 characteristics of a wire that affect its resistance. 4.A light bulb passes a current of 0.83 A when the potential difference is 120V. What is the bulb’s resistance? 5.What is the potential difference across an electric water heater element that has a resistance of 32ohms when a current through it is 6.8 A? 6.Matt says that if the resistance of a load becomes larger, the current must become larger as well. Melissa explains that the current should decrease. Who is correct? Explain.