Ch. 34 Electric Current. Movement or “flow” of charge Occurs when there is a difference in...

Ch. 34

Electric Current

Electric Current• Movement or “flow” of charge

• Occurs when there is a difference in voltage between the ends of a conductor

• Electrons carry charges through solid circuits

Electric Current (I)

Current = charge I = q

time t

• Measured in amperes (amps or A)

Example: Calculate the current where 20 coulombs of charge pass a point in 8 seconds.

Electric Current (I)

Current = charge I = q

time t

• Measured in amperes (amps or A)

Example: Calculate the current where 20 coulombs of charge pass a point in 8 seconds. 20 C / 8 s = 2.5 amps

Voltage Sources• Provide a potential difference so that

charges are able to flow– Examples: Dry Cells or Wet Cells– Energy from a chemical reaction is

converted to electrical energy

Voltage (V)

• The potential energy per coulomb of charge available to electrons moving between terminals

• Typical voltage in a home is 120 V• 120 Joules of energy are supplied to each

coulomb of charge that flows in a circuit!!!

Remember that….

Charge flows because of an applied voltage across the circuit

Electric Resistance (R)

Measured in ohms, Ω

Depends on:• Conductivity of material• Diameter of wire

– Thick wires have less resistance than thin wires

• Length of wire– Longer wires have more resistance than

shorter wires

Ohm’s Law

I = V/RCurrent = Voltage / Resistance

Units: amps = volts / ohms

I = V/RA 120 ohm heating element is powered by

a 10 volt battery. What is the current?

I = V/RA 120 ohm heating element is powered by

a 10 volt battery. What is the current?

10 V / 120 ohm = 0.083 amps

Direct Current (DC)• Charge always flow in one direction

– Ex. Batteries

Alternating Current (AC)• Charge alternates directions as it flows

– Ex. Our outlets

Since our outlets produce AC current, but many appliances use

DC, what can we do…..Convert AC to DC

• Diode: a converter that only allows electrons to flow in one direction

Electric Power

• The rate at which electrical energy is converted into another form

• Power = current x voltage

• P = IV

Ch. 34 Practice

Ch. 35 Electric Circuits

• Series Circuits

For Problem Solving in Series

• Resistances are ADDED

• R1 + R2 + R3 = R total

The resistance of one lamp is 10 ohms. What is the total resistance for the circuit shown?


R total = 10 + 10 + 10 = 30 ohms


R total = 10 + 10 + 10 = 30 ohms

If the attached voltage source is 10 V, what is the current in the circuit?


R total = 10 + 10 + 10 = 30 ohms


I = V/R

I = 10 V / 30 ohms

I = 0.33 amps

• Parallel Circuits

1 = 1 + 1 + 1

Rtotal R1 R2 R3



1/10 + 1/10 + 1/10 = 1 / Rtotal

0.3 = 1 / Rtotal

Rtotal = 1/0.3 = 3.33



Rtotal = 1/0.3 = 3.33




Rtotal = 1/0.3 = 3.33


I = V/R

I = 10 V / 3.33 ohms

I = 3 amps

Ch. 35 Lab and Practice

Ch. 34 Electric Current. Movement or “flow” of charge Occurs when there is a difference in...

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