REVIEW CIRCUITS
How to draw circuit diagrams.
1. Draw 3 bulbs in series with a cell.
- insert an ammeter to measure current through the cell.
- insert a voltmeter to measure potential difference across the cell.
Answer:
2. Draw 3 bulbs in parallel with a cell.
- insert an ammeter to measure current through the cell.
- insert a voltmeter to measure potential difference across the cell.
Answer:
You will use LEDs instead of bulbs.
** DO NOT connect the battery until I've checked your circuit.
For voltmeters and ammeters, use the smaller units.
** Read the numbers carefully. There are different scales for different connections.
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| Notice there are multiple red connections. The different connections will determine which numbers you need to read on the scale above. |
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| The numbers along the top go with one of the red connectors. The numbers on the bottom with the other connector. They will be labelled. |
Variables and Units
Potential difference (V) --> volts, V
Current (I) --> amperes, A (not milliamps)
Resistance ( R) --> Ohms, Ω
Ohm's Law
V = I x R R = V / I I = V / R
Ohmic resistors: Obeys ohm's law.
The graph of Current (I) vs. Potential Difference (V) gives a straight line.
Example:
An LED has 500 mA of current going through it and a 3.0 V battery. What is its resistance?
Given: I = 0.5 A, V = 3.0 V
Required: R = ?
Analysis: R = V / I
Solve: R = 3.0 V / 0.5 A
= 6.0 Ω
Statement: The resistance of the LED is 6.0 Ω.
MORE PRACTICE ON DRY LABS
P. 319 Table 2
Analyze and Evaluate (b).
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