Electronics Merit Badge Class 2 10/12/20151Electronics Merit Badge Class 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 National Scout Jamboree 10/12/20152

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 = amp, or.001 ma – Nanoamps (na) : 1 na = amp or ma, or.001 ua. Electronics Merit Badge Class National Scout Jamboree 10/12/20153

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) : volt, or.001 mv – Nanovolt (nv) : volt, or mv, or.001 uv. Electronics Merit Badge Class National Scout Jamboree 10/12/20154

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. Electronics Merit Badge Class National Scout Jamboree 10/12/20155

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. Electronics Merit Badge Class National Scout Jamboree 10/12/20156

More Ohm’s Law Volts = 10. Resistance = 1000Ω Compute current. I = E / R I = 10 / 1000 =.01A.01A = 10ma Question: what would the current be if the voltage was 1 V? How about 1000 V? Different forms of Ohm’s Law: E = I x R : Voltage = Current X Resistance I = E / R : Current = Voltage / Resistance R = E / I : Resistance = Voltage / Current 10V 1000 Ω Electronics Merit Badge Class National Scout Jamboree 10/12/

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 National Scout Jamboree 10/12/20158

R1 R2 R3 R_calibrate VinJ4 GND 10V 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. AB 3 4 Calibration of Ohm’s Law Board. Electronics Merit Badge Class National Scout Jamboree 10/12/20159

1 1.Remove meter leads from J4-A and J4-B. 2.Add jumper wire for J4. 3.Dial meter to 20 DCV 4.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_R Measure Voltage for R1, R2 and R3 R1 R2 R3 R_calibrate Vin J2 J3 100 ohm 50 ohm J4 GND 10V A B Electronics Merit Badge Class National Scout Jamboree 10/12/201510

Calibration Current I_cal =__________ua = ________A V_R1 = ________V V_R2 = ________V V_R3 = ________V OMHS LAW R = 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 10V Electronics Merit Badge Class National Scout Jamboree 10/12/201511

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. 3 4 Power Measurement Vin J2J3 100 ohm 50 ohm GND V+ Electronics Merit Badge Class National Scout Jamboree 10/12/201512

Power Worksheet V+ = ________V 1.Calculate power across 100 ohm resistor. P = V x V / 100 ________ W 2.Calculate power across 50 ohm resistor. P = V x V / 50 ________ W 3.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 V+ Electronics Merit Badge Class National Scout Jamboree 10/12/201513