Circuit Symbols

A V

CURRENT

Current

• Definition: The number of electrons flowing through a point in a circuit in one second

• Unit: Current is measured in amperes (A)• Measuring Device: Current is measured by an

ammeter• Naming: Named after André-Marie Ampère, a

French physicist

The Coulomb• Because the number of electrons travelling

through a circuit is astronomically high, we need a different unit of measurement

• 6.241 x 1018 is one coulomb of charge• Therefore, 1 A is one coulomb per second• Charles-Augustin de Coulomb was a French

physicist

1A = 6 241 500 000 000 000 000 electrons passing in one second

6.241 x 1018

Does the addition of light bulbs in series

change the current?

A

A

A1 A

A

A

A1 A

Series CircuitAt=A1=A2=A3…

Does the addition of light bulbs in parallel

change the current?

A

1 A3 A

A A A

A

A

1 A3 A

A A A

AParallel CircuitAt=A1+A2+A3…

Some MathRemember: Current is the number of electrons that

pass a point in a circuit every second.

Quantity Symbol

Current I

Charge Q

Time t

Qt

I =Q

I t

1. How many amps are there in a circuit where 10C of charge pass by in 6 seconds?

2. How many coulombs of charge passed by a circuit if a 10A circuit was left on for 4 minutes?

3. How long does it take 18 coulombs of charge to pass through a 200mA circuit?

Current ratings of common loads

Electrical Device (Load) Electric Current (A)

Wristwatch 0.00013

Calculator 0.002

Electric clock 0.16

Light bulb (100W) 0.833

Television 4.1

Electric drill 4.5

Vacuum cleaner 6.5

Stove element 6.8

Oven element 11.4

Toaster 13.6

Water heater element 27.3

Car started motor (V-8) 500.0

Current Kills

Even a very small

amount of current is

deadly

Perception level: 0.001A

Muscles Tingle: 0.002A

Maximum safe level: 0.005A

Muscles convulse: 0.016ABreathing affected

Severe burns: 0.200Ano breathing

Current needed for 100W bulb: 0.833A

Heart stops: 0.050A