Conceptual Physics

Physics principles and equations

With components in series, the total potential difference equals the sum of the potential differences across each component.

Ohm’s law relates potential difference, current and resistance:

ǻV = IR

With components in series, the same amount of current flows through each component.

Step-by-step derivation

Step Reason

1. ǻVtotal = ǻV 1 +...+ ǻVn totalǻV is sum of series ǻV’s

2. IRequiv = I 1 R 1 +...+ InRn Ohm’s law

3. I = I 1 = I 2 = ... = In current the same

4. Requiv = R 1 +...+ Rn divide by equal current

27.7 - Interactive problem: series wiring

The circuit to the right contains two light bulbs and a 12-volt battery. One of the light

bulbs, R 1 , has a resistance of 75 Ÿ. Your task is to determine the resistance of the

R 2 bulb.

You have an ammeter at your disposal. You drag this tool onto the circuit to

measure the current.

Use the ammeter, Ohm’s law and your knowledge of equivalent resistance in series

circuits to determine the resistance of the R 2 bulb. In order to solve the problem you

may want to first consider what the equivalent resistance of the two resistors must

be given the reading of the ammeter and the voltage shown for the battery.

Type your answer in the space provided. Press CHECK, and a message will

indicate whether your answer is correct.

You can try again by entering a new answer and pressing CHECK again.

If you have trouble solving this problem, review Ohm’s law and the section on the

equivalent resistance of resistors in series.

27.8 - Interactive checkpoint: voltage divider

Avoltage divider is often used in

circuits where the potential difference

available is too large for certain

components. A resistor is placed in

series with the sensitive component,

“using up” some of the potential

difference available. In the circuit

shown, a 5.00 V battery is connected

to a 20.0 Ÿ resistor and a sensitive

15.0Ÿ light bulb. What is the

potential difference across the light

bulb? Use equivalent resistance to

solve the problem.

Answer:

V = V

(^494) Copyright 2000-2007 Kinetic Books Co. Chapter 27