Quantifying Electricity:Charge and Current

Quantifying Electricity

Charge: Electrons do not travel alone. Instead, they travel in big groups called Coulombs.

1 e-

A big group of e-

Charge

Every Coulomb is an amount of negative charge equal to 6.25 x 1018 electrons.

1 Coulomb (imagine many electrons)

Symbol for Charge: Q

Unit of Measurement: Coulomb (C).

Charge

Charge

For example, if we say that the charge going through a load is 50 Coulombs, then

Q = 50 C

There are 6.25 x 1018 electrons in 1 Coulomb.

There are6 250 000 000 000 000 000 electronsin 1 Coulomb.

Try This.

Charge = number of e-

6.25 x 1018 e-

Calculating Electric Current

Name Unit Symbol

Charge Coulomb Q

(Problem Set Charge Question #1)

A hair dryer has 7.5 × 1021 electrons passing through it. How much charge is in the hair dryer?

Try This.

Charge = number of e-

6.25 x 1018 e-

= 7.5 x 1021 e-6.25 x 1018 e-

= 1.2 x 103 C

.: the charge is 1.2 x 103 C

Electric Current: The rate of movement of electric charge (Coulombs) from one place to another.

Quantifying Electricity

A fuse (or circuit breaker) is a connector in a circuit that is designed to open the circuit if there is too much current.

Current

Symbol for fuse

Breakers Fuses

An ammeter is a device that is used to measure current in a circuit.

Current

Symbol for ammeter Ammeter

Current is dangerous and can seriously harm a person.It only takes 6 mA to reach the heart to kill a person.

Current

Symbol for Current: I

Unit of Measurement: Ampere (A) or just Amp.

Electric Current

Electric Current

For example, if we say that the current going

through a load is 10 Amperes, then

I = 50 A

Current = ChargeTime

Ampere = CoulombSecond

I = Q

T

Calculating Electric Current

Name Unit Symbol

Current Ampere I

Charge Coulomb Q

Time Second T

(Problem Set Current Question #4)

If 240 C of charge passes a point in a circuit in 300 s, what is the current through that point in the circuit?

Try This.

I = QT

= 240 C300 s

= 0.8 A

.: the current is 0.8 A