Chapter 7 – Measuring Electricity

1. Chapter 7 – Measuring Electricity 7.1 – Voltage • A battery uses chemical energy to move charges. Volts measure the energy level in a circuit. • Adding batteries increases the amount of energy. If a battery has 1.5 V and you use 4 batteries, it is a total of 6 V.

2. Must Draw Electric charge flows from a higher energy (voltage) to a lower energy. The charge flows out the + end of the battery and back to the - terminal of the battery.

3. Measuring Voltage: • Battery – connect the voltmeter to both the +and - end of the battery; the battery should read about 1.5V • Circuits – Every point in a circuit connected to the same wire has the same voltage.

4. Copper wire is used in most electrical devices. Why?

5. The voltage is reduced in a circuit when energy is used.

6. 7.2 – Current • Current is the flow of electric charges. Electrical current can be similar to the current of water.

7. When you look at a wire, you can’t see the current. Current occurs because the e- in the battery repels the e- in the wire and so on. If there is no voltage then there is no current.

8. Remember: • Voltage difference supplies energy to make charges flow. • Current carries energy and does work.

9. Current is measured in amperes (amps). 1 amp is the flow of 1 coulomb of charge per second. In order to measure current you have to make the current flow through the meter.

10. A meter can measure AC (alternating current) or DC (direct current). AC DC Clip

11. Too much current in a wire? Circuit breakers and fuses are kinds of devices that protect circuits from too much current.

12. AC is the type of current that your house uses. In the US, current alternates 60 times per second but in Europe it reverses 50 times per second. If you travel to Europe, you need special adapters so that your electrical appliances will not be destroyed.

13. A battery only has current that flows in one direction or DC.

14. 7.3 – Resistance Conductor is a material that easily carries current. Ex: Metals An insulator is a material that does not allow current to flow, such as glass or plastic.

15. Semiconductors are between a conductor and an insulator in the ability to carry currents. Silicon is an example of a semiconductor that is used in computer chips. Electrical conductivity is the ability of a material to conduct electricity. High conductivity = good conductor Low Conductivity = good insulator

16. Resistance of an object measure how easily charges flow through it. High resistance = Difficult for current to flow Low resistance = Easy for current to flow

17. Devices that use electricity have resistance. More light bulbs = more resistance = less current Resistance is measure in ohms ( ). Voltage and resistance determine how much current flows through a circuit.

18. Physical Science: Elements. Discovery Channel School. 2002.unitedstreaming. 5 December 2007<http://streaming.discoveryeducation.com/> Parts of a light bulb: Copper wire Tungsten filament Argon gas

19. Fluorescent bulbs are more efficient because they do not create as much heat. LED’s produce more light from less electricity than any other type of light source.