Procedure 1. Set up the Snap Circuits so that you have the circuit shown below:

Question

Procedure

1. Set up the Snap Circuits so that you have the circuit shown below: With the switch set to “on,” place a bent paperclip across the terminals as shown in Figure 4—the LED should light up.

2. Place any other objects you would like to test between the terminals marked A and B in the dia gram. Test materials like wood, metal and plastic.

3. Connect the Snap Circuit wire leads to terminals A and B. Fill the Styrofoam cup about three fourths full with water, and submerge one end of each lead in the cup. Turn the switch to “on” and note any changes in the LED.

4. Turn the switch to “off,” and add 2 teaspoons of table salt to the cup; mix until it’s dissolved. Flip the switch and note any changes in the LED brightness

Questions

1. Which terminal is positive and which one is negative in the setup above? What could you do to quickly reverse the polarity of the terminals?

2. What is the voltage across the terminals? (Hint: look for the voltage of a single AA battery—are the batteries connected in series or parallel?)

3. What types of materials caused the LED to light up? Did any of your materials make the LED light up only slightly?

4. Did the LED light up when you placed the wires in the regular water? What about after you added the salt?

5. Salt water does not conduct electricity in the same way as metals, where free electrons can move throughout the material easily. Instead, when sodium chloride dissolves in water its molecules are broken up into charged particles called ions. Based on how much the LED lit up in Step 5, what can you conclude about how well the ions in the solution carry charge compared with electrons in a metal conductor?

Note: Always make sure the positive end of the diode connects to the positive side of the batterydiodes only allow current to flow in one direction Figure 4: Circuit diagram for Experiment 1

Explanation / Answer

Answers:

1) To complete the entire circuit terminal A should be connected to -Ve end while the terminal B to the +Ve end of the battery.

Hence,

Terminal A is Negative and Terminal B is positive.

Now we want to change the polarity, for that purpose we have to reverse the battery and the Diode.

2) The voltage across the two terminals is given by Ohm's law VAB=IR

But there are two batteries in the circuit,Hence two combination are possilble such as

combination 1st (series),

VAB=(I1+I2)R

combination 2nd(parallel)

VAB=[I1I2/I1+I2]R

3) By using material like wood, metal and plastic the LED will only light up for metals.

this is because of free electrons which are present in metals which causes for conduction of electric current.

Only those materials having free electron avaliable for conduction of electron can light up the LED bulb.

4) NO,that is because of no free ions are present in normal water for the conduction of electric current.

But when we add some salt such as NaCl,then there will be Na+ and Cl- ions,and water will not be electricaly neutral.

LED light up when we add some salt to normal water.

5) The positive terminal which is dopped in the salt water will attract the negative ions while the Negative terminal which is dopped in the solution will attract the positive ions.

there is crouding of ions near both the terminals after some times.

Hence the intensity of LED goes on increasing as time passes up to certain limit.

ions in the solution are also good carriers of electric current as compair to electrons in metals.

Example:Electrolytic cell

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