Current and Power

Batteries Negative terminal is ground (0 V) Not bottles of electrons! Supply energy so charge can move Cause electrons in wire to move by changing the amount of Pe electric per q or ∆V Ex) 12V battery – Positive is 12V and negative is 0V so the potential difference is 12V

Work is done to move the charge inside the battery from the negative terminal (at 0V) to the positive terminal (at +12V). As the charge leaves the positive terminal it leaves with 12J of PE electric. As the charge moves through the circuit it gives up it’s 12J of energy (lighting bulbs, running motors, etc.) The charge reaches the negative terminal with PE electric = 0J

Electric Current Current (I) is measured in Amperes (A) Q = charge that passes through a given area Current = the rate at which charges flows Note: The direction current flows is the direction POSITIVE charges would move.

Electrons are SLOW! Drift Velocity is approximately m/s 68minutes to travel 1 m Need an E field to make them move faster from one place to another

Sources of Current Current requires a potential difference Positive charges (and current) moves from high V to low V Batteries Chemical Energy to Electrical Energy Generators Mechanical Energy to Electrical Energy

Types of Current Direct Current (DC) – Move in direction – Batteries are always DC Alternating Current (AC) – Motion of charges continuously change direction – Terminals are constantly changing sign – Occurs very fast (60times a sec) – Supplied to homes and buildings

Resistance Opposition to the flow of charge Depends on the material Resistance (R) has units of Ω (ohm) FactorLesser RGreater R Lengthshorterlonger Cross Sectional AreaLargerSmaller Materialsilver, copperaluminum Temperaturelowerhigher

Resistors continued A resistor is an electrical element that – provides a specified resistance – is used in circuit boards Our skin’s resistance when wet, resistance decreases when wet with salt water, resistance decreases more perspiration decreases resistance

Ohm’s Law To figure out the strength of a resistor you would need a color chart that tells what each color means.

Electric Power Power = rate at which work is done (energy is converted) Electric work = rate at which electrical energy is converted (rate of energy transfer)

Electric Company Electric Companies charge for Energy, not power