Electric Current, Circuits, Resistance and Ohm’s law

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Electric Current, Circuits, Resistance and Ohm’s law. MHR pg. 619-632. What is Electric Current?. An electric current is: the movement of electrons ( think of a water current- movement of water)

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Electric Current, Circuits, Resistance and Ohm’s law

MHR pg. 619-632

What is Electric Current?
• An electric current is:
• the movement of electrons ( think of a water current- movement of water)
• These electrons carry energy ( in volts) and can transfer their energy to a load such as a light bulb
Formula for Current
• I = Q / Δt
• Where
• I = current ( amps)
• Q = amount of charge ( coulombs)
• Δt = change in time ( seconds)
Problem #1: Cell phone chargers
• What is the current travelling through a cell phone charger when 0.20 mC of electrons pass a point in 0.75 min?
• 4.4 x 10 -6 A
How do you measure electric current?
• Review.
• What is going on with the diagram below?
• Where would you put the ammeter?

How bright are the two light bulbs?

Analyse this circuit:

The ammeter goes ______the first light bulb.

How bright are the two light bulbs?

How much energy does each light bulb absorb?
• Measure the voltage ( change in energy) across each light bulb in the circuit below:

The light bulb that is brighter has more or less energy?

How much energy does each light bulb absorb?
• Measure the voltage ( change in energy) across each light bulb in the circuit below:

How bright are the light bulbs? How much energy does each light bulb require?

Electrical Resistance (R)
• Electrical Resistance: is a measure of how difficult it is for an electrical current to travel through a material
• High resistance materials: do not allow an electric current to pass through ( example: plastic)
• Low resistance materials: allow electric current to pass through ( example: copper)
Resistor
• An electrical device that has a specific resistance
• The units for resistor is ohms or Ώ
Ohm’s Law
• If you were to graph the amount of energy the electrons transfer to a load (V) vs the flow of electrons that pass through a load (I), the graph would look like this:
Where :

R= resistance ( Ώ)

V = potential difference ( V)

I = current ( A)

Ohm’s Law