Unit 3, Chapter 7 Integrated Science

Unit Three: Electricity and Magnetism 7.1 Voltage 7.2 Current 7.3 Resistance Chapter 7 Measuring Electricity

Chapter 7 Learning Goals Measure volts with an electrical meter. Describe the role of a battery in a circuit. Describe the transfer of energy in a circuit. Explain the relationship between voltage and energy in a circuit. Describe current as a flow of electric charge. Measure amperes with an electrical meter. Classify materials as conductors, semiconductors, or insulators. Differentiate between electrical conductivity and resistance. Explain why metals are good electrical conductors. Measure ohms with an electrical meter.

Chapter 7 Vocabulary Terms alternating current ampere battery current direct current electrical conductivity electrical insulator electrical conductor ohm resistance semiconductor volt voltage

7.1 Voltage Key Question: Why do charges move through a circuit? *Read text section 7.1 AFTER Investigation 7.1

Measuring voltage of a cell Set the meter to DC volts. Touch the red (+) lead of the meter to the (+) battery terminal. Touch the black (-) lead of the meter to the (-) battery terminal. Adjust the meter dial as necessary.

Measuring voltage in a circuit Measure the voltage across the battery exactly as before. DO NOT DISCONNECT THE CIRCUIT. NOTE: Since voltage is measured from one point to another, we usually assign the negative terminal of a battery to be zero volts (0 V).

7.1 What does a battery do? A battery uses chemical energy to move charges. If you connect a circuit with a battery the charges flow out of the battery carrying energy.

7.1 How do these batteries differ? Some are smaller and don't store as much energy. Other batteries made with Ni and Cd can be recharged. Which battery above has the greatest voltage capacity?

7.2 Current Key Question: How do charges move through a circuit? *Read text section 7.2 AFTER Investigation 7.2

Measuring Current In practical electricity, we still label current flowing from plus to minus or HIGH voltage to LOW voltage. Current can't be measured unless the charges flow through the meter.

7.2 Current is a flow of charge

7.2 Electricity in your house These devices protect you from short circuits and fires.

7.2 Which way does current flow? Either positive or negative charges can flow. It depends on the materials making up the circuit. We label circuits from high to low current.

7.3 Resistance Key Question: How well does current travel through different materials and objects? *Read text section 7.3 AFTER Investigation 7.3

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

7.3 Resistance Resistance measures how difficult it is for current to flow.

7.3 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.

7.3 Why does a bulb light? A tungsten filament has a high resistance and glows white when it reaches 2,500 o C. Argon gas inside the bulb is "inert", it doesn't chemically react with the tungsten so it protects it from air for use over and over again.