Question

Please help answer these lab questions regarding resistors and resistor networks. Thank you!

1. Suppose you have a resistor network set up and someone adds a comparatively large resistance to it in parallel. What effect with that have on the current?

2. Now suppose they add a comparatively large resistance in series. What effect with that have on the current?

3. DVMs set to “V” can measure the voltage difference between two points. Taking a measurement should not change voltage you are measuring very much. Does that mean the DVM set on “V” should have a large or small internal resistance?

4. DVMs set on “A” can also measure current through a wire. Taking a measurement should not change the current you are measuring very much. Does that mean the DVM set on “A” should have a large or small internal resistance?

Answer 1

(1,2) Net resistance of circuit decreases if a resistor is connected in parallel with the circuit while Equivalent resistance adds up in series connection. By Ohm's law we know that Current is inversely proportional to resistance. Hence , Current will increase in first case while it will decrease in second (series) case.

(3) When we use DVM to measur voltage we connects it in parallel which draws a small amount of current. This will reduce the voltage. To minimize this effect, the DVM should draw as little current as possible - which happens if its resistance is very large.

(4) To measure current DVM is connected in series but it will reduce the current in the branch of the circuit by increasing effective resistance of circuit. So, DVM must have very small internal resistance in this case.

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