Use a single “D” battery, a single bare wire and a light bulb. Find four different ways to light the light bulb using only a battery, one wire and the

Use a single “D” battery, a single bare wire and a light bulb. Find four different ways to light the light bulb using only a battery, one wire and the bulb.


Quite often one thinks that they must run electricity from the battery to the bulb. They try from either end of the battery. The bulb won’t light!

Quite often one thinks that they must run electricity from the battery to the bulb. They try from either end of the battery. The bulb won’t light!

So, what will work?So, what will work?

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There are two positions of the bulb at each end of the battery. The wire must go from a different part of the bulb to the other end of the battery.There are two positions of the bulb at each end of the battery. The wire must go from a different part of the bulb to the other end of the battery.

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Obviously, there are two important parts of the battery. The positive terminal and the negative terminal. These terminals are at opposite ends of the battery.

Obviously, there are two important parts of the battery. The positive terminal and the negative terminal. These terminals are at opposite ends of the battery.

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If you look closely at the bulb, there is a filament that glows when it is properly wired. Many filaments are coiled.

If you look closely at the bulb, there is a filament that glows when it is properly wired. Many filaments are coiled.

You will also notice that one end of the filament connects to the tip of the bulb and the other to the threads.

You will also notice that one end of the filament connects to the tip of the bulb and the other to the threads.

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In order to light the bulb with two wires and the bulb away from the battery, one wire must go from one terminal of the battery (+) to the tip of the bulb.

In order to light the bulb with two wires and the bulb away from the battery, one wire must go from one terminal of the battery (+) to the tip of the bulb.

+-

The other wire must go from the other terminal of the battery (-) to the threads of the bulb.

The other wire must go from the other terminal of the battery (-) to the threads of the bulb.

It does not matter which wire goes to the tip and which goes to the thread as long as one end of the battery is connected to one part of the bulb and the other terminal is connected to the other part of the bulb.

It does not matter which wire goes to the tip and which goes to the thread as long as one end of the battery is connected to one part of the bulb and the other terminal is connected to the other part of the bulb.

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Now we can say that we have a complete circuit.Now we can say that we have a complete circuit.

How would one define a complete circuit, which we will call just a circuit?How would one define a complete circuit, which we will call just a circuit?

A pathway for charge to flow from one terminal of the battery, through the light bulb and back to the other terminal of the battery.

A pathway for charge to flow from one terminal of the battery, through the light bulb and back to the other terminal of the battery.

A battery is an example of a “SOURCE.”A source is a device that converts some form of energy into electrical energy.

A battery is an example of a “SOURCE.”A source is a device that converts some form of energy into electrical energy.

+-

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A generator converts mechanical energy into EE.A generator converts mechanical energy into EE.

A battery converts chemical energy into electrical energy (EE).A battery converts chemical energy into electrical energy (EE).

A solar (photovoltaic) cell converts light (radiant) energy into EE.A solar (photovoltaic) cell converts light (radiant) energy into EE.

A light bulb is an example of a “LOAD.”A load is a device that converts electrical energy into some other form of energy.

A light bulb is an example of a “LOAD.”A load is a device that converts electrical energy into some other form of energy.

+-

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Other types of bulbs, CFL’s, LED’s, etc. are more effective in converting EE into light with little or no heat. Which do you think require less electricity?

Other types of bulbs, CFL’s, LED’s, etc. are more effective in converting EE into light with little or no heat. Which do you think require less electricity?

A light bulb converts EE into thermal (heat) energy and light (radiant) energy. Incandescent bulbs need a lot of heat to have the filament glow and give off a lot of light.

A light bulb converts EE into thermal (heat) energy and light (radiant) energy. Incandescent bulbs need a lot of heat to have the filament glow and give off a lot of light.

A motor converts EE into mechanical energy.A motor converts EE into mechanical energy.

A heater converts EE into thermal energy (heat).A heater converts EE into thermal energy (heat).

SCHEMATIC SYMBOLSSCHEMATIC SYMBOLS

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Battery

Light Bulb

Switch (open)

Resistor

Ammeter

Voltmeter

Wire

Junction (wires connected)

Switch (closed)

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Switch (closed)

Switch (open)

Photo of set-up. My sketches are terrible.Photo of set-up. My sketches are terrible.

Schematic of the same circuit. Schematic of the same circuit.

What does a switch do? How does it do it?What does a switch do? How does it do it?

A closed switch completes the circuit or turns the bulb on and an open switch breaks the circuit or turns the bulb off.

A closed switch completes the circuit or turns the bulb on and an open switch breaks the circuit or turns the bulb off.

Using an AmmeterUsing an Ammeter

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An ammeter measures the current flowing through the circuit.An ammeter measures the current flowing through the circuit.

Current is the flow of charge through the wires. In physics the unit for charge is a coulomb. The symbol for current is an “I” and the unit is an ampere which is abbreviated amp or A. An amp is a coulomb per second.

Current is the flow of charge through the wires. In physics the unit for charge is a coulomb. The symbol for current is an “I” and the unit is an ampere which is abbreviated amp or A. An amp is a coulomb per second.

An ammeter is wired in series in a circuit. That means that you have to break the circuit to insert the ammeter.An ammeter is wired in series in a circuit. That means that you have to break the circuit to insert the ammeter.

I would recommend an analog ammeter. When my students used the ammeter on the multimeter, they usually made a mistake and blew the fuse. It is easy to blow the fuse and not too easy to replace it.

I would recommend an analog ammeter. When my students used the ammeter on the multimeter, they usually made a mistake and blew the fuse. It is easy to blow the fuse and not too easy to replace it.


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A series circuit means that there is only one pathway for the current to flow. If you look at the circuit, the current must pass through the ammeter and then the bulb and then the switch.

A series circuit means that there is only one pathway for the current to flow. If you look at the circuit, the current must pass through the ammeter and then the bulb and then the switch.

This leads to an interesting question. What is the direction of the current?This leads to an interesting question. What is the direction of the current?

We know now that electrons move in a metal wire. So electrons flow out of the negative terminal of the battery, go through the ammeter, the light bulb, and the switch and return to the positive terminal of the battery.

We know now that electrons move in a metal wire. So electrons flow out of the negative terminal of the battery, go through the ammeter, the light bulb, and the switch and return to the positive terminal of the battery.

But, years ago we did not know about electrons! So what then?

But, years ago we did not know about electrons! So what then?

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Benjamin Franklin is credited with the idea of positive and negative charge. Positive meant an abundance of electrical charge. So it made sense to him that positive charge flowed from an abundance of charge (+) to and absence of charge (-).

Benjamin Franklin is credited with the idea of positive and negative charge. Positive meant an abundance of electrical charge. So it made sense to him that positive charge flowed from an abundance of charge (+) to and absence of charge (-).

If you look in a physics book it will say that current is the flow of positive charge from the positive terminal of the battery, through the switch, the light bulb, and the ammeter and return to the negative terminal of the battery.

If you look in a physics book it will say that current is the flow of positive charge from the positive terminal of the battery, through the switch, the light bulb, and the ammeter and return to the negative terminal of the battery.

Many electronics books use the flow of electrons for current. Make sure that you look to see which way current is defined. Also, you may want to clarify this with the event supervisor.

Many electronics books use the flow of electrons for current. Make sure that you look to see which way current is defined. Also, you may want to clarify this with the event supervisor.

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For the rest of this presentation I will use electron flow for current.

For the rest of this presentation I will use electron flow for current.


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Does it matter where we put an ammeter in a circuit?What happens to the current as it passes through the light bulb?Does it matter where we put an ammeter in a circuit?What happens to the current as it passes through the light bulb?

Let’s put the ammeter on the opposite side of the circuit. What will be different about the current?a)The current will be less.b)The current will be the same.c)The current will be greater.Make your prediction.

Let’s put the ammeter on the opposite side of the circuit. What will be different about the current?a)The current will be less.b)The current will be the same.c)The current will be greater.Make your prediction. Now wire it and see for

yourself.Now wire it and see for yourself.

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Hopefully, by now it is obvious that the current into the bulb is the same as the current out of the bulb.Hopefully, by now it is obvious that the current into the bulb is the same as the current out of the bulb.

So, it does not matter where you put the ammeter or the switch in a series circuit. The current everywhere is the same!

So, it does not matter where you put the ammeter or the switch in a series circuit. The current everywhere is the same!

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If the values for the current are not the same, make sure that you have good connections in the circuit.To convince you I put two ammeters in this circuit; one before the bulb and one after the bulb.

If the values for the current are not the same, make sure that you have good connections in the circuit.To convince you I put two ammeters in this circuit; one before the bulb and one after the bulb.

Multi-scale ammeter.Multi-scale ammeter.

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If the other wire is connected to the “50” terminal, you read the 50 mA scale.If the other wire is connected to the “50” terminal, you read the 50 mA scale.

If the other wire is connected to the “500” terminal, you read the 500 mA scale.If the other wire is connected to the “500” terminal, you read the 500 mA scale.

If the other wire is connected to the “5” terminal, you read the 5 A scale.If the other wire is connected to the “5” terminal, you read the 5 A scale.

5050500500

Only one scale can be used at a time!Only one scale can be used at a time!

Voltage or Potential DifferenceVoltage or Potential Difference

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So, the current does not change when it passes through a light bulb, then what does cause the bulb to light? To answer this there is another property that we need to measure.

So, the current does not change when it passes through a light bulb, then what does cause the bulb to light? To answer this there is another property that we need to measure.

A voltmeter measures the voltage (potential) gain at the battery (source) or the voltage (potential) drop or loss at the light bulb (load). Look back at sources and loads.A voltmeter measures the voltage (potential) gain at the battery (source) or the voltage (potential) drop or loss at the light bulb (load). Look back at sources and loads.

A voltmeter is wired in parallel to the circuit. You do not need to break the circuit. All you have to do is touch the red (+) probe of the voltmeter to the positive terminal of the battery and the black (-) probe of the voltmeter to the negative terminal of the battery. If done properly the reading should be positive. If you get a negative value you either connected the probes backwards on the voltmeter or to the battery.

A voltmeter is wired in parallel to the circuit. You do not need to break the circuit. All you have to do is touch the red (+) probe of the voltmeter to the positive terminal of the battery and the black (-) probe of the voltmeter to the negative terminal of the battery. If done properly the reading should be positive. If you get a negative value you either connected the probes backwards on the voltmeter or to the battery.

A parallel circuit has multiple paths. You are actually diverting a very tiny current through the voltmeter in order to get a reading. You will observe series and parallel circuits for light bulbs later.

A parallel circuit has multiple paths. You are actually diverting a very tiny current through the voltmeter in order to get a reading. You will observe series and parallel circuits for light bulbs later.

The symbol for voltage is a capital V and the unit is a volt, V.The symbol for voltage is a capital V and the unit is a volt, V.

Voltage or Potential DifferenceVoltage or Potential Difference

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Touch the red (+) probe of the voltmeter to the positive terminal of the battery. Touch the red (+) probe of the voltmeter to the positive terminal of the battery.

Orienting a voltmeter is a little more challenging than an ammeter.Orienting a voltmeter is a little more challenging than an ammeter.

Touch the black (-) probe of the voltmeter to the negative terminal of the battery.

If done properly the reading should be positive. If you get a negative value you either connected the probes backwards on the voltmeter or to the battery.

If you move the probes together around the circuit to the light bulb you should have the probes connected in the following orientation and the reading should be negative.

If you move the probes together around the circuit to the light bulb you should have the probes connected in the following orientation and the reading should be negative.

The value should be close to the reading at the battery, except it is negative.The value should be close to the reading at the battery, except it is negative.

WHY?WHY?

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Remember that electrons flow around the circuit from the negative terminal of the battery through the loads along the way and back to the positive terminal of the battery. The size of the current never changes.

Remember that electrons flow around the circuit from the negative terminal of the battery through the loads along the way and back to the positive terminal of the battery. The size of the current never changes.

One way to illustrate this is to say that the electrons pick up energy at the battery (positive voltage or voltage gain) and gives up its energy at the light bulb (negative voltage or voltage loss).

One way to illustrate this is to say that the electrons pick up energy at the battery (positive voltage or voltage gain) and gives up its energy at the light bulb (negative voltage or voltage loss).

You may find that the voltage loss at the light bulb is a little bit less than the voltage gain at the battery. This is due to losses in the ammeter, switch, wires; poor connections; or a combination of both.

You may find that the voltage loss at the light bulb is a little bit less than the voltage gain at the battery. This is due to losses in the ammeter, switch, wires; poor connections; or a combination of both.

Keep in mind that energy is conserved. So as one goes around the circuit in a complete loop, the voltage gains must be equal to the voltage losses.

Keep in mind that energy is conserved. So as one goes around the circuit in a complete loop, the voltage gains must be equal to the voltage losses.

Two Bulbs in SeriesTwo Bulbs in Series

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You will probably find that the sum of the voltage losses at the bulbs, V1 + V2, is close in value to the voltage gain at the battery, VS. Remember there can be other losses.

You will probably find that the sum of the voltage losses at the bulbs, V1 + V2, is close in value to the voltage gain at the battery, VS. Remember there can be other losses.

You will notice that the bulbs are very dim or maybe out, but there is still current registered on the ammeter.You will notice that the bulbs are very dim or maybe out, but there is still current registered on the ammeter.

If you are lucky the bulbs are identical and they are both the same brightness. Chances are they are not and one is dim and the other is dimmer or out.If you are lucky the bulbs are identical and they are both the same brightness. Chances are they are not and one is dim and the other is dimmer or out.

Note: In any complete loop around the circuit from the negative terminal of the battery, through the loads, to the positive terminal of the battery, and back to the negative terminal, that the sum of the voltage gains equal the sum of the voltage losses.

Note: In any complete loop around the circuit from the negative terminal of the battery, through the loads, to the positive terminal of the battery, and back to the negative terminal, that the sum of the voltage gains equal the sum of the voltage losses.


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What happens when you unscrew Bulb #1?What happens when you unscrew Bulb #1?

Bulb # 2 goes out.The ammeter indicates that the current, I ,is zero. The circuit is broken!


What happens when you unscrew Bulb #2?What happens when you unscrew Bulb #2?

Some of the older Christmas lights were wired in series and when one burned out they all went out. This drove many a person crazy trying to find out which one blew out.Some of the older Christmas lights were wired in series and when one burned out they all went out. This drove many a person crazy trying to find out which one blew out.




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4. "Christmas Lights" are often wired in series just like the circuit you just tested.a) What happens when one of the lights burns out? Why?

4. "Christmas Lights" are often wired in series just like the circuit you just tested.a) What happens when one of the lights burns out? Why?

As we just saw, as one bulb goes out (the filament breaks, which is just like unscrewing a bulb) the circuit is broken and there is no pathway for the current and all the bulbs go out.

As we just saw, as one bulb goes out (the filament breaks, which is just like unscrewing a bulb) the circuit is broken and there is no pathway for the current and all the bulbs go out.

The challenge then is to figure out which one went out and replace it.The challenge then is to figure out which one went out and replace it.


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4. "Christmas Lights" are often wired in series just like the circuit you just tested.b) We can make a string of lights in series just like the "Christmas Lights." If you were given light bulbs that are designed to operate with a voltage of 14 volts, how many would you have to wire in series before it is connected to a 120-volt outlet?

4. "Christmas Lights" are often wired in series just like the circuit you just tested.b) We can make a string of lights in series just like the "Christmas Lights." If you were given light bulbs that are designed to operate with a voltage of 14 volts, how many would you have to wire in series before it is connected to a 120-volt outlet?

Remember that the sum of the voltage gains equals the sum of the voltage losses. If the bulb is designed for 14 volts then 14x = 120 or x = 8.57. I will need nine bulbs. I had a bunch of 14 volt bulbs and wired them and it does work.

Remember that the sum of the voltage gains equals the sum of the voltage losses. If the bulb is designed for 14 volts then 14x = 120 or x = 8.57. I will need nine bulbs. I had a bunch of 14 volt bulbs and wired them and it does work.

A better suggestion: If you have an old 80 or 100 bulb string. Cut off a socket and strip the wires and then wire it to a 1.5 volt AA, C or D battery and watch it light up.A better suggestion: If you have an old 80 or 100 bulb string. Cut off a socket and strip the wires and then wire it to a 1.5 volt AA, C or D battery and watch it light up.


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4. "Christmas Lights" are often wired in series just like the circuit you just tested.c) If you have a one hundred bulb string set of lights that are wired in series, what is the voltage drop across each bulb?

4. "Christmas Lights" are often wired in series just like the circuit you just tested.c) If you have a one hundred bulb string set of lights that are wired in series, what is the voltage drop across each bulb?

ΣVGAIN = ΣVLoss

120 V = V1 + V2 + … + V100

120 V = 100VV = 1.20 volts

ΣVGAIN = ΣVLoss

120 V = V1 + V2 + … + V100

120 V = 100VV = 1.20 volts

ΣVGAIN = ΣVLoss

The voltage drop across each bulb is 1.2 voltsΣVGAIN = ΣVLoss

The voltage drop across each bulb is 1.2 volts


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So, what can we do to make both bulbs bright again?So, what can we do to make both bulbs bright again?

If we now put two batteries in series, connecting the negative terminal of the second with the positive terminal of the first, what happens?

If we now put two batteries in series, connecting the negative terminal of the second with the positive terminal of the first, what happens?

AGAIN Note: In any complete loop around the circuit from the negative terminal of the battery, through the loads, to the positive terminal of the battery, and back to the negative terminal, that the sum of the voltage gains equal the sum of the voltage losses. There is still only one path for current to travel through the circuit.

AGAIN Note: In any complete loop around the circuit from the negative terminal of the battery, through the loads, to the positive terminal of the battery, and back to the negative terminal, that the sum of the voltage gains equal the sum of the voltage losses. There is still only one path for current to travel through the circuit.

The voltage gain is doubled, the current increases, and the bulbs return to their former brightness when one bulb was wired to one battery.

The voltage gain is doubled, the current increases, and the bulbs return to their former brightness when one bulb was wired to one battery.

Two Bulbs in ParallelTwo Bulbs in Parallel

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What is different when you wire two bulbs in parallel?What is different when you wire two bulbs in parallel?

You might want to try this with one battery first.You might want to try this with one battery first.

Both bulbs are bright.V1 = V2 = VS

Both bulbs are bright.V1 = V2 = VS

Trace the path taken by the current.Trace the path taken by the current.

The current leaves the battery and it all goes through the ammeter illustrated.The current leaves the battery and it all goes through the ammeter illustrated.

Two Bulbs in ParallelTwo Bulbs in Parallel

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What happens when you unscrew bulb #1?What happens when you unscrew bulb #1?

Bulb #1 goes out.Bulb #2 stays lit about the same.The current drops (roughly in half).VS = V2 and stays about the same as before bulb #1 was unscrewed.

Bulb #1 goes out.Bulb #2 stays lit about the same.The current drops (roughly in half).VS = V2 and stays about the same as before bulb #1 was unscrewed.

What happens when you screw Bulb #1 back in and unscrew Bulb #2?What happens when you screw Bulb #1 back in and unscrew Bulb #2?

Bulb #2 goes out.Bulb #1 stays lit about the same.The current drops (roughly in half).VS = V1 and stays about the same as before bulb #1 was unscrewed..

Bulb #2 goes out.Bulb #1 stays lit about the same.The current drops (roughly in half).VS = V1 and stays about the same as before bulb #1 was unscrewed..

How is a home wired?How is a home wired?

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Using what you observed in series and parallel circuits, do you think that your house in wired in series or parallel? Explain your answer. Let’s look at the options.

Using what you observed in series and parallel circuits, do you think that your house in wired in series or parallel? Explain your answer. Let’s look at the options.

If your house were wired in series, what would happen if one light bulb blew out or was turned off?If your house were wired in series, what would happen if one light bulb blew out or was turned off?

All the other lights and appliances would go out! That’s no good!All the other lights and appliances would go out! That’s no good!

If your house were wired in parallel, what would happen if one light bulb blew out or was turned off?If your house were wired in parallel, what would happen if one light bulb blew out or was turned off?

All the other lights and appliances would stay on! That’s good!All the other lights and appliances would stay on! That’s good!

ResistanceResistance

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When you place a meter long piece of copper wire in the circuit, there should be no significant change in the current.

When you place a meter long piece of copper wire in the circuit, there should be no significant change in the current.

The voltage drop across the copper wire, VCW, will be very small. At most VCW = 0.02 V

The voltage drop across the copper wire, VCW, will be very small. At most VCW = 0.02 V

Copper wire is a good conductor so it is said to have little resistance.Copper wire is a good conductor so it is said to have little resistance.

The voltage drop across the light bulb, VB, will be close to VS.The voltage drop across the light bulb, VB, will be close to VS.


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When you replace the copper wire with a meter long piece of nichrome wire, what is different?

When you replace the copper wire with a meter long piece of nichrome wire, what is different?

It works best if you have 28 or 30 gage nichrome wire. You may be able to get a piece from your physics department in the high school.

It works best if you have 28 or 30 gage nichrome wire. You may be able to get a piece from your physics department in the high school.

The current in the ammeter goes down quite a bit.VNW becomes sizable usually more than VB.The bulb is barely lit or may not glow at all.VS = VNW + VB.

The current in the ammeter goes down quite a bit.VNW becomes sizable usually more than VB.The bulb is barely lit or may not glow at all.VS = VNW + VB.


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Nicrome wire is said to have a lot of resistance. What is resistance?Nicrome wire is said to have a lot of resistance. What is resistance?

Resistance is the property of the wire the inhibits the flow of charge.Resistance is the property of the wire the inhibits the flow of charge.

Resistance (R) is the ratio of the voltage drop across the device to the current passing through the device.

Resistance (R) is the ratio of the voltage drop across the device to the current passing through the device.

R = V/I and its unit is called an ohm, abbreviated Ω.Named after Georg Simon Ohm.R = V/I and its unit is called an ohm, abbreviated Ω.Named after Georg Simon Ohm.


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As you shorten the nichrome wire you will notice that:1)The current increases.2)VNW decreases.3)VB increases.4)The bulb finally starts to glow or gets brighter.

As you shorten the nichrome wire you will notice that:1)The current increases.2)VNW decreases.3)VB increases.4)The bulb finally starts to glow or gets brighter.

What qualities of a given wire affects its resistance?What qualities of a given wire affects its resistance?

Length, the longer the wire the greater the resistance.Length, the longer the wire the greater the resistance.

Thickness or diameter, the thicker the wire the resistance is less.Thickness or diameter, the thicker the wire the resistance is less.


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Nichrome wire will glow and get hot with a great enough voltage and current. Nichrome wire is used to give off heat in a toaster, hair dryer or space heater.

Nichrome wire will glow and get hot with a great enough voltage and current. Nichrome wire is used to give off heat in a toaster, hair dryer or space heater.

This is fun to do. If you go to Radio Shack and get a cheap rheostat and replace the nichrome wire. As you turn the knob the same thing will happen when you changed the length of the nichrome wire.

This is fun to do. If you go to Radio Shack and get a cheap rheostat and replace the nichrome wire. As you turn the knob the same thing will happen when you changed the length of the nichrome wire.

A rheostat acts as a dimmer switch or a volume control by varying the resistance.A rheostat acts as a dimmer switch or a volume control by varying the resistance.


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The symbol for a rheostat is:The symbol for a rheostat is:

The schematic of the circuit is:The schematic of the circuit is:

Short CircuitShort Circuit

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When you do this section, only close the switch long enough to take the required readings. You are KILLING the battery!When you do this section, only close the switch long enough to take the required readings. You are KILLING the battery!

What happens when you place the wire between the terminals of Bulb #1?

What happens when you place the wire between the terminals of Bulb #1?

the current, I, increases.Bulb #1 goes out.Bulb #2 gets brighter.

the current, I, increases.Bulb #1 goes out.Bulb #2 gets brighter.

VS stays the same or increases slightly.The wire gave a low resistance path around Bulb #1.

VS stays the same or increases slightly.The wire gave a low resistance path around Bulb #1.

Short CircuitShort Circuit

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When you do this section, only close the switch long enough to take the required readings. You are KILLING the battery!When you do this section, only close the switch long enough to take the required readings. You are KILLING the battery!

What happens when you place the wire between the terminals shown?


the current, I, increases a lot.Bulbs #1 & #2 go out.


VS goes to zero or close to it.The wire gave a low resistance path from one terminal of the battery to the other, mostly bypassing the bulbs.


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Short CircuitShort CircuitWhen you do this section, only close the switch long enough to take the required readings. You are KILLING the battery!When you do this section, only close the switch long enough to take the required readings. You are KILLING the battery!







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THE END!THE END!

Documents

Use a single “D” battery, a single bare wire and a light bulb. Find four different ways to light the light bulb using only a battery, one wire and the