Electrostatics (Static Electricity) was a single discharge. Current is a steady flow of electric charge.

Circuit – continuous conducting path  Only works if my circuit is composed of conductors  Conductors – allows current to flow Examples: copper, steel, iron  Insulators – restricts flow of current Examples: wood, glass, plastic

Current (I)  Defined as charge per unit time  SI unit is the Ampere (A)  Example: A steady current of 2.5 A flows in a wire for 4.0 min. a. How much charge passed through any point in the circuit? b. How many electrons would this be?

Example (worked)

Direction of Flow (**current does have a direction that it flows, but it is a SCALAR!!)  Electrons flow from the NEGATIVE terminal and are attracted to the POSITIVE terminal of the battery!  Conventional current flows the OTHER way! (This was how scientists viewed current 200 years ago!)

Resistance (R)  Similar to the friction of electricity  SI unit is the Ohm (Ω)  All objects have some measure of resistance, but INSULATORS have the most!  We use RESISTORS to control the current across electrical devices.

Ohm’s Law  In order to produce current, potential difference must be applied! (Voltage)  Circuits that follow this law are called Ohmic.  Example: A flashlight bulb draws 300 mA from its 1.5 V battery. a. What is the bulb’s resistance? b. If the voltage dropped to 1.2V, what would the current be?

Examples (worked)

Electric Power (P)  SI unit is the Watt (W)  Defined as the energy per unit time of a circuit.  Example: An electric heater draws 15.0 A on a 120 V line. How much power does it use?

Example (worked)

Example 2: Calculate the resistance of a 40W headlight designed for 12V.

Circuit Elements

Series Circuits  Resistors connected end to end  Current flows in one loop around the circuit, so All resistors have the SAME current, I  Resistors SPLIT the battery voltage  If one bulb blows (goes out) the ENTIRE circuit is broken and they ALL go out.  Equivalent Resistance is the Total resistance of the circuit.

Series Circuits (Same I, Different V)  Three resistors, 25Ω, 50Ω, and 100Ω, are connected in series. A. What is the equivalent resistance of the circuit? B. What is the current and voltage across each resistor?

Parallel Circuit  Resistors connected so that current can split.  Current splits, so I is NOT the same  Voltage is the same across each bridge  If one bulb blows out, current redirects to another so they stay lit!

Parallel Circuits (Same V, Different I)  Three resistors, 25Ω, 50Ω, and 100Ω, are connected in parallel. A. What is the equivalent resistance of the circuit? B. What is the current and voltage across each resistor?

Complex Circuits (Pre-AP)