Activities involving basic understanding of electricity, magnetism and simple electrical devices....

Science Olympiad

Shock Value

Circuit Lab

Activities involving basic understanding of electricity, magnetism and simple electrical devices.

Hopefully this will involve test type questions and hands-on activities.

Could be:•stations.•building specific circuits.•analyzing circuits.•analyzing graphs.•mapping fields.•there are many possibilities.

Series CircuitIn a series circuit the Equivalent Resistance is the sum of the individual resistances.

R3 = 6.0 ΩR1 = 4.0 Ω R2 = 8.0 Ω

RS = R1 + R2 + R3 = 4.0 + 8.0 + 6.0 = 18.0 Ω

A quick check is the Equivalent Resistance for resistors in Series is always more than the largest individual resistance.

In the above example, RS must be greater than 8.0 Ω.

Parallel CircuitIn a parallel circuit the Equivalent Resistance is the reciprocal of the sum of the reciprocal of the individual resistances.

1/RP = 1/R1 + 1/R2 + 1/R3 1/RP = 1/4.0 + 1/8.0 +1/6.0 1/RP = 13/24 Ω

A quick check is the Equivalent Resistance for resistors in Parallel is always less than the smallest individual resistance. In this case RP must be less than 4.0 Ω.

RP = 24/13 Ω = 1.85 Ω R3 = 6.0 Ω

R1 = 4.0 Ω

R2 = 8.0 Ω

Using your calculator:RP = (R1

-1 + R2-1 + R3

-1)-1 = (4-1 + 8-1 + 6-1)-1 = 1.85 Ω

Using the circuit shown below, what is the current passing through each resistor?

RS1 = R2 + R3 = 6.20 Ω + 9.80 Ω = 16.0 Ω

RS2 = R4 + R5 = 16.0 Ω + 8.0 Ω = 24.0 Ω

R1 = 5.40 Ω

30.0 V

RS2 = 24.0 Ω

RS1 = 16.0 Ω

R1 = 5.40 Ω

30.0 V

R2 = 6.20 Ω R3 = 9.80 Ω

R4 = 16.0 Ω R5 = 8.00 Ω

In analyzing circuits, you can replace any group of resistors with its equivalent.

Using the circuit shown below, what is the current passing through each resistor?

1/RP = 1/RS1 + RS2

1/RP = 1/16.0 + 1/24.0 = 5/48.0

RP = 48.0/5 = 9.60 Ω

R1 = 5.40 Ω

30.0 V

RS2 = 24.0 Ω

RS1 = 16.0 Ω

R1 = 5.40 Ω

30.0 V

R2 = 6.20 Ω R3 = 9.80 Ω

R4 = 16.0 Ω R5 = 8.00 Ω

R1 = 5.40 Ω

30.0 V

RP =9.60 Ω

Using the circuit shown below, what is the current passing through each resistor?

RTS = RP + R1

RTS = 5.40 Ω + 9.60 Ω = 15.0 ΩIS = I1 = IP = VS/RTS = (30.0 V)/(15.0 Ω) IS = I1 = IP = 2.00 A

R1 = 5.40 Ω

30.0 V

RS2 = 24.0 Ω

RS1 = 16.0 Ω

R1 = 5.40 Ω

30.0 V

R2 = 6.20 Ω R3 = 9.80 Ω

R4 = 16.0 Ω R5 = 8.00 Ω

R1 = 5.40 Ω

30.0 V

RP =9.60 Ω

Using the circuit shown below, what is the current passing through each resistor?

VP = IPRP = (2.00 A)(9.60 Ω) = 19.2 VVS1 = VS2 = VP = 19.2 V

I4 = I5 = VS2/RS2 = 19.2 V/24.0 Ω I4 = I5 = 0.80 A

R1 = 5.40 Ω

30.0 V

RS2 = 24.0 Ω

RS1 = 16.0 Ω

R1 = 5.40 Ω

30.0 V

R2 = 6.20 Ω R3 = 9.80 Ω

R4 = 16.0 Ω R5 = 8.00 Ω

R1 = 5.40 Ω

30.0 V

RP =9.60 Ω

Using the circuit shown below, what is the current passing through each resistor?

VP = IPRP = (2.00 A)(9.60 Ω) = 19.2 VVS1 = VS2 = VP = 19.2 V

I2 = I3 = VS1/RS1 = 19.2 V/16.0 Ω I2 = I3 = 1.20 A

R1 = 5.40 Ω

30.0 V

RS2 = 24.0 Ω

RS1 = 16.0 Ω

R1 = 5.40 Ω

30.0 V

R2 = 6.20 Ω R3 = 9.80 Ω

R4 = 16.0 Ω R5 = 8.00 Ω

R1 = 5.40 Ω

30.0 V

RP =9.60 Ω

Using the circuit shown below, what is the voltage drop across each resistor?

V1 = I1R1 = (2.00 A)(5.40 Ω) = 10.8 V

V2 = I2R2 = (1.20 A)(6.20 Ω) = 7.44 V

V3 = I3R3 = (1.20 A)(9.80 Ω) = 11.76 V

V4 = I4R4 = (0.8 A)(16.0 Ω) = 12.8 V

V5 = I5R15 = (0.8 A)(8.00 Ω) = 6.4 V

R1 = 5.40 Ω

30.0 V

R2 = 6.20 Ω R3 = 9.80 Ω

R4 = 16.0 Ω R5 = 8.00 Ω

I1 = 2.0 A

I2 = I3 = 1.2 A

I4 = I5 = 0.8 A

Working with circuits.

The challenge here is to be able to apply the basic concepts to a setup in the lab. Either an existing one or have you build a given circuit.

There are many ways to achieve this.

Here are some examples that were used at Nationals.

Before you is a circuit with switches, identical light bulbs and a battery holder. Draw a schematic of the circuit as if the following were true. There are batteries in both holders that were wired properly in series.• There is a voltmeter placed to measure the voltage drop across Bulb #1.• There is an ammeter placed to measure the current passing through just bulb #1.• There is an ammeter placed to measure the current passing through just bulb #3.

AA

V

Bulb #1

Bulb #2 Switch #1

Bulb #3

Switch #2

Before you is a circuit with switches, identical light bulbs and a battery holder. Draw a schematic of the circuit as if the following were true. There are batteries in both holders that were wired properly in series.• There is a voltmeter placed to measure the voltage drop across Bulb #1.• There is an ammeter placed to measure the current passing through just bulb #1.• There is an ammeter placed to measure the current passing through just bulb #3.

Breadboard or Circuit Board

A Breadboard is an easy way of wiring circuits together. It saves twisting wires together or using lots of leads with alligator clips.

Breadboard or Circuit Board

All the connections on the “X” row are connected together.

All the connections on the “Y” row are connected together.

Breadboard or Circuit Board

Columns are in two sections: 1A-1E are connected together.Same for the other columns in this section.

Columns 1F-1J are connected together, but NOT to 1A-1E or adjacent columns in this section.

Breadboard or Circuit Board

This is a picture of the breadboards that I brought along. There are many different manufacturers, but all have the two long strips on either side and the two sections of columns in between.

Breadboard Used at Nationals

There are three types of resistors used on this board. The possibilities are: Brown Green Black Gold Red Red Black GoldOrange Orange Black Gold Yellow Violet Black GoldGreen Blue Black Gold Brown Black Brown GoldRed Red Brown Gold

The first two bands give the first two digits of the resistance.The third band is the multiplier that gives the power of ten of the resistance value.The fourth band gives the tolerance of the resistor.

1st & 2nd BandBlack 0Brown 1Red

2Orange 3Yellow 4Green 5Blue 6Violet 7Gray 8White 9

3rd Band MultiplierBlack 0x100

Brown 1x101

Red 2x102

Orange 3x103

Yellow 4x104

Green 5x105

Blue 6x106

Silver -2x10-2

Gold -1x10-1

4th Band ToleranceGold 5%Silver 10%none 20%

Practice: Orange Violet Red Gold

1st & 2nd BandBlack 0Brown 1Red

2Orange 3Yellow 4Green 5Blue 6Violet 7Gray 8White 9

3rd Band MultiplierBlack 0x100

Brown 1x101

Red 2x102

Orange 3x103

Yellow 4x104

Green 5x105

Blue 6x106

Silver -2x10-2

Gold -1x10-1

4th Band ToleranceGold 5%Silver 10%none 20%

Orange Violet = 37 Red = x102 Gold = 5% TOLERANCE

37 x 102 Ω = 3700 Ω

3700 ± 5%

There are three types of resistors used on this board. The possibilities are:

Brown Green Black Gold 15 Ω

Red Red Black Gold 22 Ω

Orange Orange Black Gold 33 Ω

Yellow Violet Black Gold 47 Ω

Green Blue Black Gold 56 Ω

Brown Black Brown Gold 100 Ω

Red Red Brown Gold 220 Ω

Breadboard Used at Nationals

One exposed: Brown Green Black Gold

There are three types of resistors used on this board. The possibilities are: Brown Green Black Gold Red Red Black GoldOrange Orange Black Gold Yellow Violet Black GoldGreen Blue Black Gold Brown Black Brown GoldRed Red Brown Gold

15 Ω

Breadboard Used at Nationals

Single Resistors.

There are three types of resistors used on this board. The possibilities are: Brown Green Black Gold Red Red Black GoldOrange Orange Black Gold Yellow Violet Black GoldGreen Blue Black Gold Brown Black Brown GoldRed Red Brown Gold

Check resistance with meter.

56 Ω 220 Ω 15 Ω

Breadboard Used at NationalsNow there are some combinations.

Check resistance with meter: 55 to 56 Ω

Possible Resistors: 15 Ω, 56 Ω, 220 Ω

Four resistors in parallel. Can’t be 15 Ω or 56 Ω

1/RP = 1/220 + 1/220 +1/220 +1/220 = 4/220

RP = 55 Ω Aha, each resistor is 220 Ω

Breadboard Used at NationalsNow there are some combinations.

Check resistance with meter: 11 to 12 Ω

Possible Resistors: 15 Ω, 56 Ω, 220 Ω

Two resistors in parallel. One is 15 Ω and the other 56 Ω?

RP = (15-1 + 56-1)-1 = 11.8 Ω No way to tell which is which.

RP = (15-1 + 220-1)-1 =14.0 Ω too big

Breadboard Used at NationalsThe nasty one

Check resistance with meter: 54 - 55 Ω

R8 = ? Ω

R6 = 15 Ω R7 = ? ΩR8 = can’t be 15 Ω or 56 Ωso that leaves 220 Ω

Breadboard Used at NationalsThe nasty one

Check resistance with meter: 54-55 Ω

RS = 15 + 56 =71 Ω

R8 = 220 Ω

R6 = 15 Ω R7 = ? Ω

RP = (71-1 + 220-1)-1 = 54 Ω

Concerns:

• Less expensive meters seem to be less accurate.

• When students experiment using multimeters, they often wire an ammeter in parallel with a device creating a short and thus a large current which may blow the fuse in the meter. You may not have received replacement fuses and if you have them, they are not easy to replace (you will need a screw driver).

• If you have many teams competing at the same time, there is a need for many setups.

• Colleges and Universities have sophisticated equipment. There may be a need to explain how they function.