The Standard
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Student Task |
Charge
Electric charge is the physical property of matter. Objects can have a positive charge (like a Proton), a negative charge (like an electron) or no charge/neutral charge (like a neutron).
Like charges repel each other and unlike charges attract each other. Generally the positive nuclei of atoms are hard to move. It is easier to move the electrons that surround the nuclei in an atom. This means if a body is negatively charged it has gained electrons, so has more negative charge (electrons) than positive charge (protons). If a body has a positive charge it has lost electrons, so it has more positive charge (protons) than negative charge (electrons). Charge has the units Coulomb (C) and the symbol you will see for charge in equations is q or Q. The charge of an electron is: 1.602x10^-19 C or 0.00000000000000000001602 C |
Current
Electric current is the rate of flow of charge, it has the symbol I and the units Amperes/Amps (A).
You can calculate current by dividing the amount of charge that flows pass a point in a certain amount of time.
I = Q/t
Conventional current flows from the positive terminal to the negative terminal of a battery (from a higher electric potential to a lower electric potential)
You can calculate current by dividing the amount of charge that flows pass a point in a certain amount of time.
I = Q/t
Conventional current flows from the positive terminal to the negative terminal of a battery (from a higher electric potential to a lower electric potential)
Conductors, Insulators and Semiconductors
Conductors allow current to flow through them, this is because they have low resistance. Metals tend to be conductors because the atoms that make them up hold on to their electrons very loosely and they are free to flow.
Insulators don't allow current to flow through them, this means they have very high resistance. The atoms that make up insulators hold onto their electrons tightly, this means they can't flow easily. Semi-conductors are part way between conductors and insulators. They allow current to flow through well under certain conditions. Electrical engineers can dope and combine semiconductors to allow current to flow under certain conditions, some examples of these combinations are diodes and transistors. |
Voltage
Electrical components convert electric potential energy into other forms of energy. For example a light bulb converts electric potential energy into light and heat energy. Resistors like the ones in your toaster convert electric potential energy into heat. Motors convert electric potential energy into kinetic energy.
Batteries convert chemical potential energy into electric potential energy, so electric potential energy is gained across a battery.
Potential difference or voltage is the amount of electric potential energy lost or gained across a component per coulomb of charge.
The symbol for voltage is V and the units are volts (V).
You can calculate voltage using: V = E/q (where E is the amount of energy lost or gained)
Batteries convert chemical potential energy into electric potential energy, so electric potential energy is gained across a battery.
Potential difference or voltage is the amount of electric potential energy lost or gained across a component per coulomb of charge.
The symbol for voltage is V and the units are volts (V).
You can calculate voltage using: V = E/q (where E is the amount of energy lost or gained)
Ohm's Law
Ohm's Law states: V = IR, it can be rearranged to give: I = V/R or R = V/I
If the battery voltage remains the same and the current increases the resistance must decrease. If the battery voltage remains the same and the resistance increases the must current decrease. If the current remains the same and the resistance increases the battery voltage must increase. If the current remains the same and the battery voltage increases the resistance must increase. If the resistance remains the same and the current increases the battery voltage must increase. If the resistance remains the same and the battery voltage increases the current must increase. |
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Safety With Multimeters
Personal safety:
Damage to instrument:
Damage to the circuit:
Battery life:
- Do not use with mains or high (+50) voltages
- Check insulation on probes is in good condition
- Hold probes by the insulation
Damage to instrument:
- Always start on the highest possible scale setting and work down to give a more accurate measurement
- When measuring current always start on the 10A setting and only switch to the higher accuracy setting if the reading given is less than 0.2A
- Be careful when handling the meter: remove the probes by pulling on the plugs not the wires, do not drop or get the meter wet
Damage to the circuit:
- Do not short circuit tracking with the probes when making measurements
Battery life:
- Switch off the meter when you are finished using it
Using Multimeters
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Schematics & Symbols
This web page has an extensive and clear list of common electronic components
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Breadboarding
Breadboarding is an important skill that we need to develope this year so that we can quickly and correctly create functioning circuits from circuit schematics. You can build virtual breadboarded circuits in Fritzing, which you can download from the software page. Here is some information on how to do it:
Potential Divider
The potential divider is a really useful and important circuit in level 1 electronics. Potential divides are used to take a varying resistance from a component and convert it into a varying voltage. The varying voltage can then be used to control a transistor switch or measured as an input to a microcontroller like an Arduino.
Click on the 'www' icon to go to a useful website that explains how to calculate voltages at different points in a potential divider and how to select values for fixed resistors within the divider. |
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