Wire Resistance and Ohm’s Law

Procedure Part I Wire Resistance: open the PhET Simulation Electricity, Magnets, and Circuits Resistance in a Wire.

As wire length (cm) increases, the resistance (Ω) _increases________________

As wire area (cm2) increases, the resistance (Ω) _____decreases_____________

As wire resistivity (Ωcm) increases, the resistance (Ω) ____increases___________

Procedure Part II: Ohm’s Law: Electricity, Magnets, and Circuits Ohm’s Law mA is milliamps, and ___1000______ milliamps equals one Ampere.

• Move the potential (volts) and resistance (ohms) sliders and observe the current (amps)

As voltage increases, current _____increases_____________.

As resistance increases, current _____decreases___________.

Fill out the tables below and check your work in the simulation. ( ½ pt each )

• Remember, the simulation shows milliamps.

• You should show Amperes V = I * R

8.0 V .1 A 800 Ω

2.0 V .044 A 450 Ω .2 V .0058 A 430 Ω 6.9 V .069 A 100 Ω

6.4 V .0213 A 300 Ω

Conclusion Questions: ( ½ pt each)

1. Incandescent light bulbs have a very thin filament that glows when hot. Thin filaments have very high / low resistance.

2. The 12V battery in your car operates a 25 amp car stereo. What is the resistance of this stereo system? __.48 ohms_________

3. A “2D” Maglite flashlight runs on 3.0V. What is the current through the bulb if resistance is 15 Ω ? _.2 amps___________

4. How many volts must an iPod charger provide to charge an iPOD using .85 Amps at 35 Ω? _29.75 volts____________

5. You need to buy a long extension cord to power a stereo at your spring break BBQ. You need 200feet. You have a 50 ft cord that will work. You rationalize that four such 50 ft cords will do the job. Is this a good idea? Why or Why not?