1. PHYSICAL SCIENCE Electricity Part 2: Current

2. 13.2 Current Objectives Describe how batteries are sources of voltage. Explain how a potential difference produces a current. Define resistance. Calculate the resistance, current, or voltage, given the other two quantities. Distinguish between conductors, superconductors, semiconductors, and insulators.

3. Voltage and Current Electrical potential energy is the potential energy of a charged object due to its position in an electric field. A negative charge will move away from another negative charge. The electrical potential energy of the moving charge decreases because the electric field does work on the charge. A force can push a charge in the opposite direction of the electric force which acts to increase the electrical potential energy.

4. Voltage and Current Potential difference is the change in the electrical potential energy per unit charge. The SI unit for potential difference is the volt (V), which is equivalent to 1 joule per coulomb. The potential difference of batteries can range from 1.5 V to 12 V. Most common batteries are an electric cells that convert chemical energy into electrical energy.

5. Voltage and Current Cells contain an electrolyte, a solution that conducts electricity, and two electrodes, each a different conducting material. Wet cells, like a car battery, contain a wet electrolyte. Dry cells, like those in a flashlight, contain a paste-like electrolyte. The average cell has a potential difference of 1.5 V between the positive and negative terminals.

6. Dry Cell

7. Wet Cell

8. Voltage and Current In a flashlight, electrons move through the light bulb from the negative terminal to the positive terminal. An electric current is produced when charges are accelerated by an electric field to move to a position of lower potential energy. Current is the rate at which electric charges move through a conductor. The SI unit for current is the ampere (amp).

9. Voltage and Current One amp equals one coulomb of charge moving past a point in one second. The charges always move from one terminal to the other in the same direction for direct charge. In metals, moving electrons make up the current, in gases and most solutions, current is the result of the movement of positive and negative charges.

10. Voltage and Current Conventional current is defined as movement of positive charge so the direction of current in a wire is opposite the direction that electrons move in that wire. Nerve signals are in the form of a changing voltage across the nerve cell membrane.

11. Sodium-Potassium Pump

12. Electrical Resistance Resistance is the ratio of the voltage across a conductor to the current it carries. Resistance is caused by internal friction, which slows the movement of charges through a conducting material. The resistance of a dim 40 W light bulb has a higher resistance than the filament of a bright 100 W light bulb. In most materials, some of the kinetic energy of electrons is lost as heat.

13. Resistance in Light Bulbs

14. Electrical Resistance Resistance = voltage/current or R=V/I The SI unit of resistance is the ohm (  ), which is equal to volts per amp. A resistor is a special type of conductor used to control current. Every resistor is designed to have a specific resistance.

15. Georg Simon Ohm and Ohm’s Law

16. Electrical Resistance A good conductor is any material in which electrons can flow easily under the influence of an electric field. Metals tend to make excellent conductors because electrons can move freely through them. Superconductors are metals and compounds that have zero resistance when their temperature falls below the critical temperature. The critical temperature of materials varies.

17. Electrical Resistance Insulators have high resistance to charge movement. Insulating materials are used to prevent electric current from leaking. One may need to provide a pathway for current to leave a charged object and do so by means of grounding. Semiconductors have properties between those of conductors and insulators.