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Unit 7: Electricity and Magnetism 19.1 Electric Circuits 19.2 Current and Voltage 19.3 Electrical Resistance and Ohm’s Law Chapter 19 Electricity

Unit 7: Electricity and Magnetism

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Unit 7: Electricity and Magnetism. Chapter 19 Electricity. 19.1 Electric Circuits 19.2 Current and Voltage 19.3 Electrical Resistance and Ohm’s Law. Chapter 19 Objectives. Describe the difference between current and voltage. - PowerPoint PPT Presentation

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Page 1: Unit 7: Electricity and Magnetism

Unit 7: Electricity and Magnetism

19.1 Electric Circuits19.2 Current and Voltage 19.3 Electrical Resistance and Ohm’s Law

Chapter 19 Electricity

Page 2: Unit 7: Electricity and Magnetism

Chapter 19 Objectives1. Describe the difference between current and

voltage.2. Describe the connection between voltage,

current, and resistance.3. Describe the function of a battery in a

circuit.4. Make calculations and inferences in a circuit

using Ohm’s law.5. Draw and interpret a circuit diagram with

wires, battery, bulb, and switch.6. Give examples and applications of

conductors, insulators.

Page 3: Unit 7: Electricity and Magnetism

Chapter 19 Vocabulary Terms electricity electric current voltage resistance Ohm’s law battery open circuit closed circuit

circuit diagram electrical

conductor wire volt electrical

symbols Wire Load Bulb Switches Battery Cell

voltmeter ohm resistor ammeter electrical

insulator electric circuit amperes

(amps)

Page 4: Unit 7: Electricity and Magnetism

19.1 Electric CircuitsKey Question:What is an electric circuit?

Page 5: Unit 7: Electricity and Magnetism

19.1 Electric Circuits Electricity refers to the

presence of electric current in wires, motors, light bulbs, and other devices.

Electric current is similar to a current of water, but electric current flows in solid metal wires so it is not visible.

Electric current can carry a lot of power.

Page 6: Unit 7: Electricity and Magnetism

19.1 Electric Circuits An electric circuit is something that provides a

complete path through which electricity travels.

Wires in electric circuits are similar in some ways to pipes and hoses that carry water.

Page 7: Unit 7: Electricity and Magnetism

19.1 Electric Circuits When drawing a circuit diagram, symbols are

used to represent each part of the circuit. These electrical symbols are quicker and

easier to draw than realistic pictures of the components.

Page 8: Unit 7: Electricity and Magnetism
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19.2 Current and Voltage

Key Question:How does current

move through a circuit?

Page 12: Unit 7: Electricity and Magnetism

19.2 Current and voltage

Electric current is measured in units called amperes, or amps (A) for short.

One amp is a flow of a certain quantity of electricity in one second.

The amount of electric current entering a circuit always equals the amount exiting the circuit.

Page 13: Unit 7: Electricity and Magnetism

19.2 Voltage Voltage is a measure of

electric potential energy, just like height is a measure of gravitational potential energy. Voltage can also be referred to as potential difference

Voltage is measured in volts (V).— Did you know that…… a

voltage difference of 1 volt means 1 amp of current does 1 joule of work in 1 second.

Page 14: Unit 7: Electricity and Magnetism

19.2 Voltage The positive end of a 1.5

volt battery is 1.5 volts higher than the negative end.

If you connect batteries positive-to-negative, each battery adds 1.5 volts to the total.

Three batteries make 4.5 volts.

Each unit of current coming out of the positive end of the three-battery stack has 4.5 joules of energy.

Page 15: Unit 7: Electricity and Magnetism

19.2 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.

Page 16: Unit 7: Electricity and Magnetism

19.2 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). Use the other lead to check the voltage on each side of the bulbs in your two bulb series and two bulb parallel circuits

Page 17: Unit 7: Electricity and Magnetism

19.2 Current and voltage A battery uses chemical

energy to create a voltage difference between its two terminals.

In a battery, chemical reactions provide the energy to pump the current from low voltage to high voltage.

A fully charged battery adds energy proportional to its voltage.

Page 18: Unit 7: Electricity and Magnetism

19.2 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.

Page 19: Unit 7: Electricity and Magnetism

19.2 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?

Page 20: Unit 7: Electricity and Magnetism

19.2 Current is a flow of charge

Page 21: Unit 7: Electricity and Magnetism

19.3 Electrical resistance

Resistance measures how difficult it is for current to flow.

Page 22: Unit 7: Electricity and Magnetism

19.3 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.

Page 23: Unit 7: Electricity and Magnetism

19.3 The ohm

Resistance is measured in ohms (W).

One ohm is the resistance when a voltage of 1 volt is applied with a current of 1 amp.

Page 24: Unit 7: Electricity and Magnetism

19.3 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.

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Page 26: Unit 7: Electricity and Magnetism

19.3 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.

Page 27: Unit 7: Electricity and Magnetism

19.3 The resistance of electrical devices

The resistance of electrical devices ranges from very small (0.001 Ω) to very large (10×106 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.

Page 28: Unit 7: Electricity and Magnetism

19.3 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.

Page 29: Unit 7: Electricity and Magnetism

19.3 Electrical Conductivity The electrical conductivity describes a

material’s ability to pass electric current.

Page 30: Unit 7: Electricity and Magnetism

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.