# Electricity Notes

#### Units of charge

A coulomb is a unit of charge in the metric system. It is 6.25 × 10^{18}
electrons. The symbol for charge is q.

- Conductors: pass electricity. Metals, salt solutions.
- Insulators: Block electricity

#### Electric Potential

A charge in an electric field has a potential energy based on the strength of the
electric field

#### Current

Current: the amount of electrical charge flowing through a wire per second.

Current is measured in Amperes: One ampere is one coulomb per second. The symbol
for current is an i. The symbol for Amperes is just an A.

If a light bulb is rated to use 0.8 A, that means 0.8 Amperes or 0.8 coulombs per
second.

If 0.5 amperes pass through a light during an eight hour night, how many coulombs of
charge passed through the light?

i =q/t 0.5 A = q/(8 hrs*3600sec/hr)

0.5 = q/28800

q= 14400 Coulombs of charge

##### Electromotive Force (*EMF*)

*EMF* is the force that impels electrons to move. EMF is the energy per
coulomb of charge. Remember that energy is also called work in physical science.

*EMF* = work/q or *EMF* = energy (Joules)/charge (Coulomb)

*EMF* is also called "voltage" because the units of EMF are Volts.

Using i =q/t we can write q = it
(t is time)

Therefore EMF = energy/ it (substituted it for charge q). Now the energy per unit time is power.

*EMF* = 1/i ×energy/time

*EMF* = 1/i ×power

*EMF* × i = power

We also use V for *EMF* (for voltage) hence we often write **V × i = power **

The voltage (Volts) times the current (Amperes) is the power (Watts)

A typewriter uses 0.8 Amps at 100 Volts. How many Watts of power does the
typewriter consume? iV = Power: (0.8 Amps)(100 Volts) = 80
Watts. Answer: 80 Watts.

How many amps (short for amperes) runs through a 100 Watt light bulb on Pohnpei?
The Voltage on Pohnpei is 118 Volts during the day.

P = iV

100 Watts = i (118 Volts)

i (Amperes) = 100 Watts/118 Volts