0.4 Hydrogen and fuel cells  (Page 4/4)

Powering an LED

• One fuel cell does not generate enough voltage to power anything of interest. Just like you would connect 2 or 4 AA batteries in series to power a portable CD player, it is necessary to connect multiple fuel cells to generate larger voltages.
• Pair up with another group and connect the positive terminal of one cell to the negative terminal of the other cell using the wires with alligator clips. Now connect the unwired positive terminal to the positive (longer lead) of the red LED. The unwired negative terminal should be connected to the negative (short lead) of the red LED. At this point the LED should be lit. If you do not see any light, you should use the multimeter to check the voltage generated by the two cells in series and verify that it is greater that 1.5V. If you do not measure any voltage verify that you have wired everything correctly.

Figure 5: Powering an LED circuit.

Powering a small motor

• While two cells in series generate the proper voltage to operate the motor, they cannot source enough current to run a motor longer than a few seconds. By putting cells in parallel more current can be obtained.
• You will need two sets of two cells in series as described in the “Powering an LED” section (4 groups are needed for this part).
• Take the positive connection from each series cell and connect to one terminal of the electric motor. Take the negative connection from each series cell and connect to the other terminal on the electric motor. At this point the motor shaft should begin to turn. If not, check the wiring and verify that you are applying at least 1.5V. It is also possible that 2 parallel cells will not generate enough current. Additional cells can be added in parallel to generate more current.

Figure 6: Powering a motor circuit.

Pre-lab: (total 10 points)

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

This assignment must be completed individually and turned in to your TA at the beginning of lab. You will not be allowed to begin the lab until you have completed this assignment.

1.Fill in the blanks:

Fuel cells are used for direction conversion of the energy of combustion reactions to ______________. A fuel cell is a ______________ in which electricity is generated by a combustion reaction. A fuel cell provides a ______________ voltage that can be used to power motors, lights or any number of electrical appliances.

2.T or F At the anode, oxidation of the fuel takes place.

3.T or F The fuel cell emissions will be nothing but water vapor.

4.T or F The efficiency of fuel cells, chemical-to-electric energy conversion, is approximately 40%.

Review of series and parallel circuits:

In a series circuit, the electrons in the current have to pass through all the components, which are arranged in a line. Consider a typical series circuit in which there are three resistors of value R1, R2, and R3.

• The current throughout the circuit is the same.
• The voltages add up to the battery voltage.

Therefore:

VT = V1 + V2 + V3

From Ohm’s Law:

• VT = IRT;
• V1 = IR1;
• V2 = IR2;
• V3 = IR3

Þ IRT = IR1 + IR2 + IR3

Therefore:

RTot = R1 + R2 + R3

5.In the circuit below, the current is 100 mA.

(a) What is the current in each resistor?

(b) What is the voltage across each resistor?

(c) What is the total resistance?

(d) What is the battery voltage? 

In this case, the current will split into three.   For a parallel circuit:

• The voltage across each branch is the same.
• The currents in each branch add up to the total current.

From this:

Itot = I1 + I2 + I3

From Ohm’s Law:  I T = V ; I1 = V; I2 = V; I3 = V

RT R1 R2 R3

Þ V = V + V + V

RT R1 R2 R3

Þ 1/RTot = 1/R­1 + 1/R2 + 1/R3

6.This question refers to the circuit below.

(a) What is the total resistance of the circuit?

(b) What is the current through each resistor?

(c) What is the total current? 

For resistors in both series and parallel, follow these guidelines:

• Work out the total resistance of the parallel combination.
• Work out the total resistance of the circuit by adding your answer in the previous step to the values of the series resistors.

7.What is the single resistor equivalent of this circuit?

Report (80 points)

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’ work (including your laboratory partner) or misrepresent your own data (see honor code).

The following tables and questions should be answered in your written report. Please put the information in the relevant section of your report (i.e. observations and results, discussion)

What would happen if zinc screws were used instead of brass?

What is the purpose of the palladium coating on the anode?

What is the purpose of the palladium coating on the cathode?

What fuel cell worked best?

Explain, in detail, why you think that the best fuel cell worked better than the others?

Debate fuel cells.