Electric Circuits

Electric Circuits

• Current electricity is the flow of electrons (current) through a closed path that is made of a conductive material (i.e. copper)
• The electrons get their “push” to move through a circuit from a battery or any other source of voltage, like a generator (more on this later)
• The electrons travel INTO any device you put along the path; they do “work” at the device, turning it on
• Electrons return to the battery to restart the cycle

A Simple Electric Circuit

A way to make electrons do some work for us

Circuit Components-Battery

• Batteries are properly referred to as voltaic cells
• A battery/voltaic cell: has two metal terminals called electrodes
• Chemical reactions that involve those 2 metals produce electrons
• Electrons will move from the negative electrode of the battery, through the circuit and back to the positive electrode
• If you place a device in the electron’s path, electrons move through the device, providing their energy to the deviee
• Note that a battery is a two or more voltaic cells put together

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A Battery-Two Or More Cells

Circuit Components:

• Conducting wires that allow electrons to flow through
• Made of a conducting material like copper or aluminum
• Covered by insulating wire (to prevent shock)
• Device/Resistor/Load that we want to work. The device will convert the electron’s electrical energy into another form of energy
• Ex: electric kettle converts electrical energy to heat energy

Circuit Components

• Switch that closes and opens a circuit, determining whether the electrons can reach the device
• Closed path to connect all the components
• This closed path is called an electric circuit
• Allows uninterrupted flow of electrons from the negative terminal of a battery and back again to the positive terminal of the battery
• At the battery, the electrons will get “recharged”, and are ready to go for another round of work…

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Circuit Components

• The flow of electrons through a circuit is called a current
• Electrons always move in one direction through the conducting wires of a circuit
• From negative terminal of a battery to the positive terminal
• You can describe a circuit with words, but it is more practical for us to use a circuit diagram
• These diagrams are maps that anyone can read to see how to build a certain circuit

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Symbols In Circuit Diagrams

Ammeter

• An instrument that measures electric current
• Its symbol in an electric circuit is

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• How to read an ammeter or voltmeter

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Electric Current (I)

• Electric current is the rate of movement of electrons at a specific point in an electric circuit. We give it the symbol I
• It is amount of charge (electrons) that passes a point in a conducting wire every second
• Instead of talking about the charge on individual electrons, we talk about the charge on a “chunk” of electrons (or a coulomb)

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One coulomb= the charge on 6.25 x 10¹⁸ electrons

It’s like saying: a dozen eggs is 12 eggs..

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Electric Current (I)

• To calculate current, you can use the following formula:
• I= Q Current= charge (C)

T time (s)

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Charge is measured in coulombs (C), time in seconds

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However, instead of writing the unit of current as C/S, we say that current is measured in amperes (A)

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Sample Current Problem

• Question: 600 C of charge pass a point in a conducting wire every three minutes. What is the current through that point in the conductor? Use Grasp!

Given: Analyse and Solve:

Q=600 C

T=3 minutesx60=180s I=Q/T

Required: I=600C/180s

I=? I= 3.33 A

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Paraphrase: The current going through that specific point in the wire is 3.33 amperes.

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Voltage

• If we want meaningful information about how much work electrons can do when they enter a device, we need to measure how much energy (measured in joules) each coulomb of charge is getting so…J/C. This quantity is known as the volt (V)
• Voltage is the energy provided by a battery to the electrons in a circuit. It is the electrical pressure that causes electrons to move
• The higher the voltage, the more energy the electrons have
• Therefore, a 9V battery provides 9 j/c or 9V to the electrons; a 3V battery only provides 3j/c or 3V

Voltage Or Potential Difference

• V=E voltage= energy (measured in J)

Q charge (measured in C)

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• Voltage always compares the potential energy the electrons have at two points in a circuit (ex: before a device and after it)
• i.e. if voltage across a bulb is measured at 1.5V, that means the electrons lost 1.5 V of energy to make it through that device (we say there was a voltage drop of 1.5 V)
• Measured using an instrument called a voltmeter

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Sample Voltage Problem

• A battery provides 15 coulombs of charge with 45 joules of energy. What is the voltage of the battery? Use Grasp!

Given: Analyse and Solve:

Q=15 C

E= 45 J V=E/Q

Required: V=45J/15C

V=? V= 3 V

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Paraphrase: A 3 volt battery is able to provide 15 coulombs of charge with 45 joules of energy.

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