electricity. electricity: the movement of “excited” charged particles electric current: what the...
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• 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
• Batteries pump energy (potential energy) into a circuit
• 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?
Closing the switch establishes a potential difference (voltage) and an electric field in the circuit.
• Electrons flow in a net direction away from the (-) terminal.
High Potential
Low Potential
Conventional Current• By tradition,
direction in which “positive charges” would flow.
• Direction is opposite of electron flow.
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?
• 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.
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
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.
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– 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)
• Abbreviate with R• Unit is Ohm (Ω)
• Measured outside of a circuit
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