1. Current - rate at which charge passes a given point.
Electric Current
Current - rate at which charge passes a given point.

2. Current
The higher the current is, the more charge passes the point each second.
Unit for current is ampere (A) or amp
In equations, the symbol for current is I
2 Different types of electric current:
Direct current (DC) - charges flow in same direction
Alternating current (AC) - charges continually switch from flowing in one direction to flowing in the reverse direction.

3. Currents Cont’d DC - Electric current produced by batteries and cells
AC - used in outlets in your home

4. Voltage The current in a wire is determined by voltage.
Voltage - the difference in energy per unit charge as a charge moves between 2 points in the path of a current.
Another word for potential difference.
Expressed in Volts (V).
The amount of energy released as a charge moves between 2 points in the path of a current.
The higher the voltage = the more energy is released per charge
The greater the voltage = the greater the current

5. In the US, electrical outlets usually supply a voltage of 120 V.
Most electrical devices (TV’s, toasters, lamps, alarm clocks) are designed to run on 120 V.
Devices that run on batteries or cells usually need a lower voltage

6. Resistance Also determines the current in a wire.
Resistance is the opposition to the flow of electric charge.
Expressed in ohms (Ω)
In equations the symbol for resistance is R
Think of resistance as “electrical friction”
The higher the resistance, the lower the current
As resistance increases, current decreases
Varies depending on the objects material, thickness, length and temperature.

7. Good conductors have low resistance.
Poor conductors have higher resistance.
The resistance of insulators is so high that electric charges do not flow in them.
Materials with low resistance are used to make wires and other objects that are used to transfer electrical energy from place to place.

8. Resistance vs. Temperature
Resistance of metals increases as temperature increases
This happens because atoms move faster at higher temperatures and get in the way of the flowing electric charges.
If you cool certain materials to an extremely low temperature, resistance will drop to nearly 0 ohms.
These materials are called superconductors.
Little energy is wasted when electric charges travel in them, but it takes a lot of energy to cool them so they aren’t very practical.

9. Amperes (A) = volts (V)/ohms (Ω)
Ohm’s Law
Amperes (A) = volts (V)/ohms (Ω) OR
I = V/R

10. Try These!
Find the resistance of an object if a voltage of 10 V produces a current of 0.5 A.
Find the current produced if a voltage of 36 V is applied to a resistance of 4 Ω.

11. Electric Power The rate at which electrical energy is used to do work.
Unit for power is the watt (W)
The symbol for power is P
Power = voltage x current or P = V x I
Watts = volts (V) x amperes (A)

12. Measuring Electrical Energy
Electrical Energy = power x time
E = Pt