Electricity

Electricity: the movement of “excited” charged particles Electric current: what the moving charged particles create Like water moving through pipes Electric circuit: the path an electric current follows Like pipes and utilities that use water.

Conductors: materials in which electric current flows easily Usually metals Graphite is a form of carbon, but it is a conductor Insulators: materials that do NOT allow electric current to flow easily

Measuring Electricity Voltage: measures the difference in energy between two places in the circuit. Measured in volts (V) Black – Red + Measure V across two spots on a closed circuit

Batteries The more batteries, the more energy (voltage) Batteries provide an electric potential difference to a circuit, causing electrons to flow. This potential difference is called “voltage”. The more batteries, the more energy (voltage) Each battery is 1.5 V (carbon-zinc batteries)

How much voltage will 12 batteries have? How many batteries do you need if you have a an alarm clock that requires 9 V?

Voltage is a difference in energy between two points.

Electrons flow in a net direction away from the (-) terminal. Closing the switch establishes a potential difference (voltage) and an electric field in the circuit. High Potential Low Potential Electrons flow in a net direction away from the (-) terminal.

Conventional Current By tradition, direction in which “positive charges” would flow. Direction is opposite of electron flow.

Conventional Current vs. Electron Flow We can thank Ben Franklin for the conventional (and WRONG) current direction. He called one side positive because he thought that was the side that had the excess electrons, so “positive” meant surplus. We now now that it’s the negative side with the surplus and that’s why it’s negative. So, electron flow is nefgative to positive.

While the switch is open: Free electrons (conducting electrons) are always moving in random motion. The random speeds are at an order of 106 m/s. There is no net movement of charge across a cross section of a wire.

What occurs in a wire when the circuit switch is closed?

What occurs in a wire when the circuit switch is closed? An electric field is established instantaneously (at almost the speed of light, 3x108 m/s). Free electrons, while still randomly moving, immediately begin drifting due to the electric field, resulting in a net flow of charge. Average drift velocity is about 0.01cm/s.

Electric Current: The flow of electric charges.

Conventional current has the direction that the (+) charges would have in the circuit.

Voltage Drop Voltage drops across something that uses energy (light bulb, heater, etc) Energy drops because work is done

Measuring Electricity Current (I) Measured in amperes, or amps (A) Measure in an open circuit Electricity must flow through the meter to measure current

Resistor: something that uses energy in a circuit

Circuit Diagrams Draw a diagram of a circuit that contains two batteries, a switch, a resistor, and a light bulb. Draw a diagram of a circuit that contains a battery, a switch, a potentiometer, and two light bulbs (in that order).

Did you know… Voltage is painful Current kills More volts, the greater the shock A bolt of lightning can have more than 1,000,000 volts Current kills Small amounts of current can be deadly (especially through the heart)

Resistance Resistance (load): something that opposes the flow of electricity Energy is used (work is done) ALL electronic devices are resistors. Abbreviate with R Unit is Ohm (Ω) Measured outside of a circuit

Potentiometers Potentiometers: a variable resistor. Dimmer switches are variable resistors. When you turn the resistance down, the light burns brightly. When you turn the resistance up, the bulb is dimly lit.

Examples Determine the current in a circuit that has a resistance of 40 Ω and a voltage of 1.5 V

Examples Determine the voltage in a circuit that has a resistance of 10 Ω and a current of 5 mA