Electronics Merit BadgeClass 2

04/19/23 1Electronics Merit Badge Class 2 - 2013 National Scout Jamboree

Resistance• Resistance is an electrical property of a

material that “resists” the flow of electrons. • The schematic symbol for a resistor is:• Common units for resistance are:– Ohms– Kilohm: 1K= 1000 ohms, 10K = 10,000 ohms– Megohm: 1M = 1,000,000 ohms

• The units symbol for ohms is: Ω (ohms)

Electronics Merit Badge Class 2 - 2013 National Scout Jamboree04/19/23 2

Current

• Current: Defined as “flow of electrons”.• Current: Units of current is AMPS.• Current: Electrical symbol for current is I.• Common units for current are:– Amps– Milliamps (ma): 1 ma = .001 amp– Microamps (ua) : 1 ua = .000001 amp, or .001 ma– Nanoamps (na) : 1 na = .000000001 amp

or .000001 ma, or .001 ua.

Electronics Merit Badge Class 2 - 2013 National Scout Jamboree04/19/23 3

Voltage• Volts is the electrical force that causes electrons (current) to flow.• Units of volts is VOLTS.• The symbol of volts is E.• Common units for voltage are:– Volts– Millivolt (mv) : .001 volt.– Microvolt (uv) : .000001 volt, or .001 mv– Nanovolt (nv) : .000000001 volt, or .000001 mv, or .001

uv.

Electronics Merit Badge Class 2 - 2013 National Scout Jamboree04/19/23 4

Power

• Power is the measure of how much energy a circuit or appliance uses.

• Power is measured in Watts (W).• The symbol for power is P.• Power is calculated by: P = E x I.• Typical units are watts, killowatts (1000

watts), megawatts (1,000,000) watts, etc.

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Ohms Law

• One of the most important laws in electronics/electricity.

• E = I x R : Voltage = Current x Resistance• Volts is measure in VOLTS, current is measured

in AMPS, and resistance is measured in OHMS.• 1 AMP, going through 1 OHM of resistance,

generates a voltage drop of 1 VOLT.• 1 V = 1 A x 1 Ω.

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More Ohm’s Law

Volts = 10.Resistance = 1000ΩCompute current.I = E / RI = 10 / 1000 = .01A.01A = 10maQuestion: what would the current be if thevoltage was 1 V? How about 1000 V?

Different forms of Ohm’s Law:E = I x R : Voltage = Current X ResistanceI = E / R : Current = Voltage / ResistanceR = E / I : Resistance = Voltage / Current

10V

1000 Ω

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+

Ohm’s Law Board

• We will use the ohm’s law board to illustrate that ohm’s law really works. You will also learn how to use a meter.

• The purpose of this board is to use ohm’s law to calculate the value of 3 resistors.

• Also, we will calculate the amount of power two resistors dissipate, and notice the difference between the two.

Electronics Merit Badge Class 2 - 2013 National Scout Jamboree04/19/23 8

R1

R2

R3

R_calibrate

Vin J4

GND

10V

1

2

1. Turn on meter (->1)2. Dial meter to 2000u DCA (->2)3. Place meter lead (mA -> 3) to J4-A.4. Place meter lead (COM -> 4) to J4-B.5. Turn Board ON.6. Adjust R_Calibrate until meter reads 1000 ua

(as close as you can get it.)7. You now know how much current goes

through R1, R2 and R3. Write this down as I_cal on worksheet.

8. NOTE: 1000 ua (microamp) = 1 ma (milliamp) = .001 A (amp). We will use .001 A when we calculate resistance.

A B

34

Calibration of Ohm’s Law Board.

Electronics Merit Badge Class 2 - 2013 National Scout Jamboree04/19/23 9

1

1. Remove meter leads from J4-A and J4-B.2. Add jumper wire for J4.3. Dial meter to 20 DCV4. Place VΩmA lead (2) at top of R1.5. Place COM lead (3) at bottom of R1.6. Read the voltage from the meter and write

it on worksheet for V_R1.7. Connect the meter to top and bottom of R2

and write down this voltage as V_R2.8. Do the same for R3. Write down the

voltage as V_R3.

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Measure Voltage for R1, R2 and R3

R1

R2

R3

R_calibrate

Vin

J2 J3

100 ohm

50 ohm

J4

GND

GND

10V

A B

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Calibration Current I_cal =__________ua

= ________A

V_R1 = ________V

V_R2 = ________V

V_R3 = ________V

OMHS LAWR = E/I

R1 = ________Ω

R2 = ________Ω

R3 = ________Ω

OHM’S LAW WORK SHEET

R1

R2

R3

R_calibrate

Vin

J2 J3

100 ohm

50 ohm

J4

GND

GND

10V

Electronics Merit Badge Class 2 - 2013 National Scout Jamboree04/19/23 11

1

1. Connect wire across J2.2. Dial meter to 20 DCV (1)3. Connect meter VΩmA lead (3) to V+.4. Connect meter COM lead (4) to GND.5. Read the meter and write down the

measured voltage.6. Voltage measured at V+ = _________V.

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Power Measurement

Vin

J2 J3

100 ohm

50 ohm

GND

GND

V+

Electronics Merit Badge Class 2 - 2013 National Scout Jamboree04/19/23 12

Power Worksheet

V+ = ________V1. Calculate power across 100 ohm

resistor. P = V x V / 100 ________W

2. Calculate power across 50 ohm resistor.

P = V x V / 50 ________W3. Touch 100 ohm and 50 ohm

resistors quickly with your fingers. What is different between the 2? Why are they different?

Vin

J2 J3

100 ohm

50 ohm

GND

GND

V+

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