Volts is electrical pressure - the potential difference measured between 2 points in a circuit
Amps is electrical current - the flow of current in a circuit from positive to negative
Ohms is electrical resistance - the opposition to current flow in a circuit
Watts is electrical power - the electrical energy in a circuit
Click here to see Ohms law using Volts, Amps, Ohms and Watts
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To measure electrical units we need to use an instrument called a meter. |
| Meters come in all shapes and sizes, each for a different purpose. We can have special purpose meters that measure just one type of unit such as watts or an instrument called a multimeter which is capable of measuring volts, amps and ohms. |
| Even though the multimeter can measure three electrical units, the meter must be connected differently in the circuit. |
To measure Volts - connect the meter in parallel with the circuit under measurement while connected to the supply.
To measure Amps - connect the meter in series with the circuit under measurement while connected to the supply.
To measure Ohms - connect the meter in parallel with the circuit under measurement with the supply disconnected.
Click here to learn more about meters Click here to learn more about Oscilloscopes (CRO)
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Multiples and sub-multiples |
| Meters come in all shapes and sizes, each for a different purpose. We can have special purpose meters that measure just one type of unit such as watts or an instrument called a multimeter which is capable of measuring volts, amps and ohms. |
|
Electrical measurements can be from thousands of amps to millionths of an amp.
Terms used for these measurements 'kilo' and 'milli' are called multiples and sub-multiples.
|
| A few examples are listed in the following table: |
Term
Symbol
Multiplier
Example
mega
M
1,000,000
107MHz = 107,000,000 Hz
milli
m
0.001
6mA = 0.006 A
micro
u
0.000001
2uA = 0.000002 A
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Conversion Examples: |
| Question: A resistance reading is 4.7 Megohms. How many ohms does this represent? |
| Answer: Mega is one million so multiply 4.7 by 1,000,000 by moving the decimal point six places to the right 4,700,000 ohms |
| Question: There is 2.45 mA flowing in a circuit. How many amps is this? |
| Answer: Milli is one thousand so divide 2.45 by 1,000 by moving the decimal point 3 places to the left 0.00245 amps |
Scientific Notation |
| Scientific Notation is a way of expressing multipliers (see previous table) in mathematical form. Each multiplier is treated as a power of 10. Following are examples scientific notation using the examples from the previous table: |
Term
Symbol
Multiplier
Example
Scientific Notation
mega
M
1,000,000
107MHz = 107,000,000 Hz
106
kilo
k
1000
5kV = 5000 V
103
milli
m
0.001
6mA = 0.006 A
10-3
micro
u
0.000001
2uA = 0.000002 A
10-6
|
Conversion Examples: |
| Question: Convert 10kV to volts |
| Answer: |
| 10kV |
= |
10 x 103 V |
(k = 103) |
| |
= |
100 x 102 V |
(1 decimal place right) |
| |
= |
1000 x 101 V |
(2 decimal places right) |
| |
= |
10000 x 100 V |
(3 decimal places to right) |
| 10kV |
= |
10,000 V |
|
|
| Question: Convert 0.10mA to microamps (uA) |
| Answer: |
| 0.10mA |
= |
0.10 x 10-3 A |
(m = 10-3) |
| |
= |
1.0 x 10-4 A |
(1 decimal place right) |
| |
= |
10 x 10-5 A |
(2 decimal places right) |
| |
= |
100 x 10-6 A |
(3 decimal places to right) |
| 0.10mA |
= |
100 uA |
(u = 10-6) |
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