1. Voltage, Current, and Resistance
Electricity
Voltage, Current, and Resistance

2. Electric Potential Energy
Because of the attractive or repulsive force between charges, it takes energy for the charge to hold a certain position.
The energy a charge has depends on how close it is to another charge.
This is called “electric potential energy”.

3. Voltage (V)
The potential energy difference is called “voltage”, which provides the “push” that moves the charge.
Voltage is the potential energy per charge.
unit: volts (v)
1 volt = 1 joule of energy
1 coulomb of charge

4. Battery
A battery is a device that uses chemical energy to move charges
The charges that flow out of the battery carry energy. These charges give their energy to electrical devices.

5. Voltage Voltage is the measure of the energy level in a circuit.
Ex. A fully charged battery adds 1.5 volts of energy.
Stacking the batteries
can make higher voltage

6. Measuring Voltage
Voltage 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

7. Voltage drop
Every point in a circuit connected to the same wire is the same voltage.
Every time you connect something that uses energy, the amount of voltage is reduced since it takes energy away from the moving charges in the wire

8. 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.

9. Current (I) Current is the rate of the flow of the electrical charges
unit: Ampere, Amps (A)
1Amp = 1 coulomb of charge/second
Current flows from the positive terminal of a battery to the negative terminal or from high voltage to low voltage.
Charge does not flow unless there is a potential difference.

10. 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.
Something that provides a potential difference is called a voltage source
ex: battery, generator, dry cell, friction to build a static charge

11. Measuring Current
I = q / t
I = current (A)
q = electric charge (C)
t = time (sec)
To measure current, the charges must flow through a meter ….. you must connect the meter into your circuit so the current is forced to flow through it

12. Conductivity
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 does not allow charges to flow
A semiconductor is between a conductor and an insulator. Most computer chips are semiconductors

14. Types of Current
A battery produces direct current (DC). A battery makes current flow in one direction
AC current is easier to generate and transmit.
Electricity in your house is alternating current (AC). This means the direction of the current goes back and forth. … which means the electrons stay in the same relative place
House outlets typically have a potential difference of 120 V
Fuses and Circuit breakers protect us by breaking circuits when too much current is being used which prevents overloading and wires from getting overheated

15. Resistance (R)
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.

16. Resistance
unit: 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
high resistance …. long, thin, hot
low resistance …. short, thick, cold

17. Ohm’s Law V = voltage (volts) I = current (amps) R = resistance (ohms)
V = I R
V = voltage (volts)
I = current (amps)
R = resistance (ohms)

18. Ohm’s Law and Electric Shock
The resistance of your skin can range from 100 ohms (wet skin)to about 500,000 ohms (dry skin).
Why is it dangerous to work with electrical equipment near water?

19. In order for a shock to occur, there must be a difference in electrical potential between one body part and another.
This is why a bird can stand on a live electrical wire and not get electrocuted.
(Notice both feet are touching the wire at ALL times!!)

20. Electric Power (P) P = I V P = power (watts) I = current (amps)
Power is the amount of energy used in a second
1 watt = 1 joule of energy / 1 second
unit: watts (w)
P = I V
P = power (watts)
I = current (amps)
V = voltage (volts)

21. Introductory Video watch: Magic School Bus Gets Charged
complete the accompanying assignment.
*go to Announcements page of Mrs. Espinosa’s website*