Activity 4: Ohm's Law

Aim: To find the relationship between voltage, current and resistance.

Hypothesis: As voltage increases, current increases. As resistance increases, current decreases.

Theory Background:

Voltage is an electrical potential difference. It is the potential energy that makes the electrical current flow in a circuit by pushing the electrons around. The unit of voltage is volt (V). Electric current is the rate which a charge flows through a surface. It is measured in Ampere (A). Resistance is a measure of how material resist the flow of an electrical current. It is measured in Ohm (Ω). Ohm’s law states that V=I x R. It shows that V is directly proportional to I and R. So, as the voltage increase, the current and resistance will also increase. This formula also shows that current and resistance are inversely proportional- as current increases, the resistance will decrease.

Manipulative Variables:

Independent: Current, Resistance, Voltage

Controlled: Formula (V=IR)

Dependent: Relationship between voltage, current and resistance.

Materials:

• Formula

Method:

• Move the potential and resistance sliders and observe the current
• Fill in the tables and check with the formula

Data Collection:

Procedure Part 1:

As the resistance increases, current decreases

As voltage increases, current increases

Procedure Part 2:

V = I        x R

Voltage (V)	Current (I)	Resistance (R)
8.0 V	0.01 A	800 Ω
2.0 V	0.044 A	45.45 Ω
2.49 V	0.0058 A	430 Ω
6.9 V	0.069 A	100 Ω
6.4 V	0.021 A	300 Ω

Conclusion:

1. Incandescent light bulbs have a very thin filament that glows when hot. Thin filaments have very high resistance.
2. The 12 V battery in our car operates a 25 amp car stereo. The resistance of the stereo is 0.48 Ω
3. A “2D” Maglite flashlight runs 3.0 V. The current through the bulb is 5 A when the resistance is 15 Ω
4. An iPod charger must provide 29.75 V to charge an iPod using 0.85 amps at 35Ω
5. It is not a really good idea, because when we rationalize that four such 50 ft cords will do the job, the resistance will four times higher and the voltage drop will be four times higher as well. Due to the voltage drop, it is not enough to power a stereo.

Resources:

• http://www.physicsclassroom.com/class/circuits/u9l3c.cfm
• http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmlaw.html
• http://www.designcabana.com/knowledge/electrical/basics/voltage/

-Shannisya, Naomi, Andra, Ibram

10 Centaurus