Summer Research Program for Science Teachers

Traci Collier

HS for Information Technology, Queens

August 2003

How does an electric charge move?

Standards: S1c, S4a, S4b, S4d, and S5f.

M6a,c, and m.

Skills: Comprehension, relating concepts, and mathematical operations.

Vocabulary: electrical potential difference, volt, voltage, battery (wet/dry), thermocouple, photocell, electric current, circuit, ohm, resistance, superconductors, amperes, DC, and AC

Formulas: I=V/R Amperes Volts/Ohms

Curriculum Integration: Mathematics

Motivation: The “Energizer Bunny” commercials on television.

Lesson Development (including key questions):

Ø      The amounts of work required moving a charge bet 2 points, or work per unit charge is called electric potential difference between two points.

Ø      The unit of EPD is called volt (V).  Voltage is used for potential difference

Ø      Potential difference can positive or negative depending on direction

Medial: Define EPD, volt, and voltage

Batteries

Ø      A battery is a device that produces electricity by converting chemical energy into electrical energy.

Ø      A battery is made of several smaller units called electric cells, or electrochemical cell.

Ø      Wet cell battery: car battery

Ø      Dry cell battery: flashlight battery

How a wet cell works?

Ø      Zn/C electrode.  The part of the electrode that sticks up is called the terminal.  The electrolyte is sulfuric acid.  Acid attacks the Zn and dissolves it.  Electrons are left behind on the Zn electrode.  Zn negatively charged.  A series of chemical reactions pulls electrons electric off the C electrode ( positively charged)

Ø      Thermocouple is a device that produces electrical energy from heat energy.

Ø      It releases charges as a result of temperature change.

Ø       Photocells: light energy is absorbed releasing electrical energy.

Medial: Describe how a wet cell works.  What is the difference between a thermocouple and photocell?

LD Continued:

Electric Current

Ø      A circuit is a complete path.

Ø      Charges can flow through circuit.

Ø      A flow of charge is called an electric current.

Ø      The symbol for current is I.

Ø      The unit for current is ampere (A).

Ø      The instruments used to measure current are galvanometers and anmeters.

Ø      Opposition to the flow of electric charge known as resistance (R).

Ø      The unit of resistance is ohm (W).

Ø      Ohm’s Law: The current (I) in a wire is equal to the voltage (v) divided by the resistance (R).

Mini-Activity: How to calculate current (I)?

 Current (I) Voltage Resistance 12 75 15 240 5.5 20 6 25

Step1: Write formula.

Step2: Manipulate formula if necessary.

Step3: Input information according to the variable it matches.

Step4: Perform mathematical operations

Current Direction

Ø      Electrons traveling in the same direction is called direct current. (Dry cell, etc.)

Ø      Electrons traveling back and forth, reversing direction regularly is called alternating current.

Summation

Ø      EPD amount of work required moving a charge.

Ø      Volt (V)

Ø      Dry cell/wet cells

Ø      Batteries, photocell, thermocouple

Ø      Instruments used are galvanometers and anmeters.

Homework

1.      How does an electrochemical cell produce an electric current?

2.      What is thermocouple? A photocell?

3.      What is the electric current? Explain how current flows through a wire.

4.      What is resistance? Voltage? How is electric current related to resistance and voltage?

5.      What is direct current? Alternating current?

Critical Thinking

If the design of a dry cell keeps electrons flowing steadily, why does a dry cell go “dead”?