Electricity and Magnetism  16.1 Electrical Potential Energy  16.2 Equipotentials and Electric Fields  Capacitance and dielectrics  17.1 Batteries and Direct Current  : Current, Drift Velocity, Resistance  17.4 Electrical Power Chapter 16 Voltage, Energy, and Capacitance Chapter 17 Current and Resistance

Chapter 19 Objectives  Describe the difference between current and voltage.  Describe the connection between voltage, current, energy, and power.  Describe the function of a battery in a circuit.  Calculate the current in a circuit using Ohm’s law.  Draw and interpret a circuit diagram with wires, battery, bulb, and switch.  Measure current, voltage, and resistance with a multimeter.  Give examples and applications of conductors, insulators, and semiconductors.

Chapter 19 Vocabulary Terms  electricity  electric current  voltage  resistance  Ohm’s law  battery  open circuit  closed circuit  short circuit  switch  circuit diagram  electrical conductivity  potentiometer  wire  volt  electrical symbols  amperes (amps)  multimeter  ohm  resistor  ammeter  electrical insulator  semiconductor  conductor  electric circuit

19.2 Voltage  Voltage, volts (V),is a measure of electric potential energy per charge)  It is just like height is a measure of gravitational potential energy.

 Work is the potential energy:  W=qEr  Q’s cancel. V=Er

19.2 Voltage  Voltage measures the available electrical power that flows.  P=IV current*voltage  1 joule per second is a watt (power)  1000 W happening for 1 hr is a kwh.

19.2 Voltage  The positive end of a 1.5 volt battery is 1.5 volts higher than the negative end.  Batteries positive-to-negative, adds volts to the total.  Each unit of current from the + end of a three-battery stack has 4.5 joules of energy.

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.

19.1 Electric Circuits Key Question: What is an electric circuit?

19.1 Electric Circuits  Electricity refers to the presence of electric current  Electric current is similar to a current of water  Electric current can carry a lot of power.

19.1 Electric Circuits  An electric circuit must have a complete path through which electricity travels.  Wires and electric circuits are similar to pipes carrying water.

19.1 Electric Circuits  A circuit diagram uses symbols to represent each part  These electrical symbols are quicker and easy to draw

Current flows from + to -

19.2 Current and Voltage Key Question: How does current move through a circuit?

19.2 Current and voltage  Conventional current describes the + as what is moving.  Scientists later found that the particles that carry electricity actually travel from negative  Today, we still use Franklin’s definition.

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.

19.2 Current is a flow of charge

19.2 Current and voltage  A battery uses chemical energy to create a voltage (add potential energy) between its two terminals.  Chemical reactions provide the energy to pump the current from low to high V.  A fully charged battery adds energy proportional to its voltage.

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?

19.2 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.

19.3 Electrical Resistance and Ohm’s Law Key Question: How are voltage, current, and resistance related?

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

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.

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

19.3 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.

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.

law/ohms-law_en.html Ohm’s Law

19.3 The resistance of electrical devices

 Everything is designed with a resistance made for the voltage it was designed for.

19.3 Changing resistance  The resistance of many materials increases as temperature increases.  Resistors are devices with constant resistance V=IR so R=V/I  would show a straight line on this graph.

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

e-in-a-wire/resistance-in-a-wire_en.html Resistance in a Wire Conductors still have resistance.

19.3 Conductors and insulators  Copper is a conductor because it can conduct, or carry, electric current.  Materials that insulate (or block) current flow are electrical insulators.  Semiconductors are neither conductors nor insulators

19.3 Resistors  Resisters resist current flow  Resistors have striped color codes to record their "values" (writing on them is difficult).

19.3 Potentiometers  Potentiometers are a type of "variable" resistor  They are wired so that as you turn the knob, it changes the distance the current has to flow.

Application: Hybrid Gas/Electric Cars

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.

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).