Transcript Electronics Class 2

Electronics Merit Badge
Class 2
3/25/2016
Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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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)
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Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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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.
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Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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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.
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Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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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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Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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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
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
3/25/2016
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?
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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.
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Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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Calibration of Ohm’s Law Board.
Vin
A
J4
10V
B
1
2
R1
GND
3
4
R2
R3
R_calibrate
1.
2.
3.
4.
5.
6.
7.
8.
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Turn on meter (->1)
Dial meter to 2000u DCA (->2)
Place meter lead (mA -> 3) to J4-A.
Place meter lead (COM -> 4) to J4-B.
Turn Board ON.
Adjust R_Calibrate until meter reads 1000 ua
(as close as you can get it.)
You now know how much current goes through
R1, R2 and R3. Write this down as I_cal on
worksheet.
NOTE: 1000 ua (microamp) = 1 ma (milliamp)
= .001 A (amp). We will use .001 A when we
calculate resistance.
Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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Measure Voltage for R1, R2 and R3
Vin
A
J4
B
1
J2
10V
J3
R1
GND
2
3
R2
100
ohm
50
ohm
R3
GND
R_calibrate
1.
2.
3.
4.
5.
6.
7.
8.
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Remove meter leads from J4-A and J4-B.
Add jumper wire for J4.
Dial meter to 20 DCV
Place VΩmA lead (2) at top of R1.
Place COM lead (3) at bottom of R1.
Read the voltage from the meter and write
it on worksheet for V_R1.
Connect the meter to top and bottom of R2
and write down this voltage as V_R2.
Do the same for R3. Write down the
voltage as V_R3.
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OHM’S LAW WORK SHEET
Vin
Calibration Current
I_cal =__________ua
J4
= ________A
J2
10V
J3
R1
GND
R2
100
ohm
50
ohm
R3
GND
V_R1 = ________V
R1 = ________Ω
V_R2 = ________V
R2 = ________Ω
V_R3 = ________V
R3 = ________Ω
R_calibrate
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Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
OMHS LAW
R = E/I
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Power Measurement
Vin
1
V+
J2
J3
3
4
GND
100
ohm
50
ohm
GND
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1.
2.
3.
4.
5.
Connect wire across J2.
Dial meter to 20 DCV (1)
Connect meter VΩmA lead (3) to V+.
Connect meter COM lead (4) to GND.
Read the meter and write down the
measured voltage.
6. Voltage measured at V+ = _________V.
Electronics Merit Badge Class 2 - 2013 National Scout Jamboree
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Power Worksheet
Vin
V+
V+
J2
J3
GND
100
ohm
50
ohm
GND
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= ________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?
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