Electric circuits

1 / 17

# Electric circuits - PowerPoint PPT Presentation

Electric circuits. Electric Circuits. Recall: Terminal = electrode = +ve and –ve ends Metal component on cell that supplies electrons (-ve) or receives electrons (+ve) Must be connected to other components to complete a circuit Open circuit – has a gap or a break Electrons can’t flow.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## PowerPoint Slideshow about 'Electric circuits' - liuz

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

### Electric circuits

Electric Circuits
• Recall: Terminal = electrode = +ve and –ve ends
• Metal component on cell that supplies electrons (-ve) or receives electrons (+ve)
• Must be connected to other components to complete a circuit
• Open circuit – has a gap or a break
• Electrons can’t flow
Electric Circuits
• There are 4 essential components of a circuit:
• Source of electrical energy
• Generator – converts mechanical energy (motion) to electrical energy
• Cell – converts chemical energy to electrical energy
• Battery – 2 or more connected cells
• Conducting wires
• Metal wires connect all parts of the circuit
Electric Circuits
• Provides resistance to electron flow
• A device that transforms electrical energy to another type of energy
• Light bulb (lamp)
• Motor
• Switch - a control device that completes or breaks the circuit
• Fuse or circuit breaker
Electric Current
• River current = the volume water that flows past a certain point in a specific time (m3/s)
• Fast current = more water per second
• Electric current = a measure of the number of electrons that flow past a point in a circuit every second
• Electrons are too numerous to count, so they are grouped into coulombs (C)
Electric Current
• Amount of electrons or “charges” = coulombs
• given the symbol “q”
• 1 coulomb (1.0 C) of negative charge = 6.25 x 1018 electrons
• Ebonite rod – 1 millionth of a coulomb
• Carpet zap – billionth of a coulomb
• 1 coulomb of charge -100 W light bulb in 1 s
• 10 to 200 C of charge – lightning bolt

}

Don’t need to copy

Electric Current
• Electric current is given the symbol “I” and is measured as “the # of coulombs that travel past a certain point in a circuit per second”
• I = # of Coulombs/second
• I = q/t
• q/t = Ampere “Amp” (A)

I = current (A)

q = charge (C)

t = time (s)

• Current is measured with an ammeter (connected in a series)
Electric Current
Sample Problems

Lets try these together, record the steps on your handout.

• How many coulombs (or how much charge) pass through a 0.8 A, 100 W bulb in 15 minutes?
• I = 0.8 A
• t = 15 min x 60 s/min = 900 s
• Find q
• q = It
• q = (0.8 A)(900 s)
• q = 720 C
• Therefore, 720 C of charge pass through a 100W bulb in 15 min.
Sample Problems

Lets try these together, record the steps on your handout.

• If 1584 C of charge pass through a toaster in 3 minutes, what is the current through the toaster?
• q = 1584 C
• t = 3 min x 60 s/min = 180 s
• Find I
• I = q/t
• I = 1584 C/ 180 s
• I = 8.8 A
• Therefore, the current through the toaster is 8.8 Amperes
Sample Problems

Lets try these together, record the steps on your handout.

• How many coulombs of charge pass through a 11.7 A microwave oven in 2 minutes?
• I = 11.7 A
• t = 2 min x 60 s/min = 120 s
• Find q
• q = It
• q = (11.7 A)(120 s)
• q = 1407 C
• Therefore, 1407 C of charge pass through the microwave oven in 2 minutes
Electric Potential
• Energy = ability to do work
• Unit: Joule (J)
• Electrons move through a circuit, pick up energy at power source, and give some up at each load
• Total energy picked up = total lost during trip around circuit
• ELECTRIC POTENTIAL = amount of energy carried per coulomb (q)

Volts = Joules/coulomb

V = J/C

Potential Difference (aka: Voltage)
• Energy gained or lost by each Coulomb of electrons is the potential difference
• What we are really measuring is the change in electric potential of electrons from one point in the circuit to another
• Unit is Volt (V)
• V = E/q
• V= potential difference (V)
• E = energy (J)
• q = charge (C)
Potential Difference
Resistance
• It is easier to run through air than through water. Why?
• It's also easier to slide a chair over a smooth kitchen floor than over a thick carpet. Why?
• Electrons meet with more resistance when they go through some materials than others
• Lose some of their electrical energy as heat energy.
• Good conductors have very low resistance
• Eg) Heating element
Resistance
• Resistance of something depends on:
• The material
• The length of object
• The diameter
• The temperature
• R = V/I
• Ratio:

potential difference across a load : the current going through the load

Resistance