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Electricity. Circuit. Electricity is the flow of electric current in wires, motors, lights bulbs, and other devices Electric current carries energy great distances Electric circuits provides a path through which electricity flows.

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Presentation Transcript
  • Electricity is the flow of electric current in wires, motors, lights bulbs, and other devices
  • Electric current carries energy great distances
  • Electric circuits provides a path through which electricity flows
  • Electric charge is a fundamental property of matter
  • There are two different charges: positive charge and negative charge
  • Like charges repelUnlike charges attract
static electricity
Most matter is neutral with equal amounts of positive and negative.

If a material or object carries excess positive or negative charge it is electrically charged

Static electricity is the buildup of positive or negative charges

Static Electricity
  • Electric charge is measured in coulombs.
  • Protons have a positive charge of 1 coulomb
  • Electrons have a negative charge of –1 coulomb
  • An electroscope is a device used to detected charged objects
  • The leaves in a charged electroscope attract or repel each other depending on the charge nearby
  • A battery is a device that uses chemical energy to move charges
  • The charges flow out of the battery carry energy. These charges give their energy to electrical devices.
  • Voltage is the measure of the energy level in a circuit.
  • A fully charged battery adds 1.5 volts of energy.
  • Stacking batteries can

make higher voltage

measuring voltage
Volts measures the energy difference between two places in the circuit

Since voltage is measured from one point to another, the negative terminal of a battery has 0 volts.

Measuring Voltage
voltage drop
Voltage drop
  • Every point in a circuit connected to the same wire is the same voltage.
  • Every time you connect something that uses energy, some of the voltage is reduced since it takes energy away from the moving charges in the circuit.
The single bulb circuit is much brighter, because all of the energy is used up in one bulb

Two bulbs are dimmer than just the one, because they each get only half the energy

In both circuits all of the 1.5 volt is used by the light bulbs

***No matter how many bulbs are present all of the voltage must be used in the circuit.

  • Current is the rate of the flow of the electrical charges.
  • Current is measured in Amps
  • Current is a measure of the number of charges that move in a second
  • Current flows from the positive terminal of a battery to the negative terminal or from high voltage to low voltage.
measuring current
Measuring Current
  • To measure current, the current must flow through a meter
  • That means you must connect the meter into your circuit so the current is forced to flow through it
types of current
Types of Current
  • Electricity in your house is alternating current (AC). This means the direction of the current goes back and forth. In the U.S. the current reverses 60 times per second. (In Europe is reverses 50 times per second).
  • AC current is easier to generate and transmit.
  • A battery produces direct current (DC). A battery makes current flow in one direction.
current flow
Current Flow
  • When you look at a wire, you can’t see current. The particles that carry charge are electrons
  • Batteries do not provide most of the charges that flow. The charges are already in the wire.
  • An electrical conductor is a material, like most metals, that allow current to travel
  • An electrical insulator is a material, like plastic or glass, that do not allow charges to flow
  • A semiconductor are between conductors and insulators. Most computer chips are semiconductors
  • Electrical conductivity is the property of material to allow charge to flow.
  • Materials with high conductivity, like metals, allow charge to flow.
  • Materials with low conductivity, like plastic, block charge from flowing.
  • The resistance of an object measures how easily charges flow through.
  • High resistance means it is difficult for current to flow (high resistance = low current).
  • Devices that use electrical energy have resistance.
  • The unit for resistance is called ohm (W).
  • There are three factors that affect the resistance of a copper wire: length, diameter, temperature.
      • The thicker the wire (bigger the diameter) the easier current can flow.
      • The longer the wire the harder for current to flow.
      • The higher the temperature the harder for current to flow.
ohm s law
Ohm’s Law
  • Ohm’s Law is a relationship between voltage, current, and resistance

Voltage (volts, V)

Resistance (ohms, W)

Current (amps)

electrical quantities
Electrical Quantities
  • Amps = Current is what flows in a circuit. Current is the rate of charge flow.
  • Volts = Voltage measures the potential energy differences between two places in the circuit. Voltage differences make current flow
  • Ohms = Resistance measures the ability to resist the flow of current
The slope of a current vs. voltage graph shows the resistance of a circuit

If the graph goes through the point (0,0) then you can calculate the resistance using R=V/I form of Ohm’s Law.

electrical power
Electrical Power
  • Power is the rate at which energy is flowing.
  • The unit of power is the watt (W)
  • Electric companies charge for the energy you use, which depends on how many watts each appliance consumes in

a given month.

where does the power go
Where does the power go?
  • Electrical power is easily transformed into many different forms.
  • An electric motor takes electrical power and makes mechanical power
  • A light bulb turns electrical power into light
  • A toaster oven turns the power into heat.

Voltage (volts)

Sometimes a larger unit of power is needed. A kilowatt (kW) is equal to 1000 watts

Current (amps)

Power (watts)



  • Utility companies charge customers in kilowatt-hour (kWh).
  • 1 kilowatt-hour means that 1 kilowatt of power has been used for one hour.




Different appliances have different power ratings.

  • On the back of most appliances is a listing of the power rating of the appliance.
  • From this information you can estimate the cost of running an appliance for a period of time.
Series circuitthe current can only take one path.

Parallel circuitthe current has more than one path where the current can split up.

household circuits
Household circuits
  • Electrical Circuits in homes are parallel.
    • Parallel circuits mean that a light in your home can be on at the same time the TV is off. If the house was connected in series, turning anything electrical off in your house would turn everything off
  • Most holiday lights are parallel. If one light bulb goes out, the rest stay on.
series circuits
Series Circuits
  • In a circuit, all the current flows through a single path.
  • The current is the SAME at all points in the circuit.
  • The amount of current is determined by the voltage and resistance of the circuit.

At the beginning, every charge has 3 volts of energy. As the charges move through the circuit, each light bulb is used by each bulb. All 3 volt of energy is

used by the circuit

how to find current resistance of a series circuit
How to find current, resistance of a series circuit
  • Each resistance in a series circuit adds to the total. Add together the resistance of each component in the circuit
  • Once you know the resistance and the voltage use Ohm’s Law (I = V/R) to calculate the current
  • As the current flows along a series circuit, each resistance uses up some of the energy.
  • If the voltage of the battery is 1.5 V then each light bulb will use part of the original voltage.
    • If you have 3 light bulbs than each bulb uses 1/3 of the total voltage or 1/3 of 1.5 = 0.5 V
    • If you have 2 light bulbs than each bulb uses ½ of the total voltage or 1/3 of 1.5 = 0.75 V
parallel circuit
Parallel Circuit
  • A parallel circuit has at least one point where the circuit divides. Each path is called a branch.
  • In a parallel circuit the voltage is the same across each branch. Each branch has a path back to the battery without any other resistances in the way.
current in a parallel circuit
Current in a Parallel Circuit
  • The amount of current in each branch depends on the resistance in the branch.
  • The lower the resistance in a branch means more current will flow through that branch
short circuit
Short Circuit
  • A short circuit is a circuit path with zero or very low resistance
  • Since the resistance is very low, most of the current will travel through the short circuit
  • Short circuits are dangerous because they generate a high current and a great deal of heat.