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In a piece of copper wire, the electrons are in random motion with no direction. To produce a current flow, the electrons must all move in the same direction. To produce motion in a given direction, energy must be imparted to the electrons in the copper wire. This energy comes from a source connected to the wire. The force that causes the electrons to move in a common direction is referred to as difference of potential, or voltage. This module examines how voltage is produced.
What you are expected to learn
What you are expected to learn
At the end of this module, you should be able to:
Identify the six most common voltage sources.
Describe six different methods of producing electricity.
Define a cell and a battery.
Describe the difference between primary and secondary cells.
Describe how cells and batteries are rated.
Identify ways to connect cells or batteries to increase current or voltage output or both.
Define voltage rise and voltage drop.
Identify the two types of grounds associated with electrical circuits.
How to learn from this module
How to learn from this module
Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some
tips for you:
1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.
2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.
3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.
4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.
5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.
What to do before (Pretest)
What to do before (Pretest)
Lesson 4: VOLTAGE
Lesson 4: VOLTAGE
• Current is produced when an electron is forced from its orbit.
• Voltage provides the energy to dislodge electrons from their orbit.
• A voltage source provides a means of converting some other form of energy into electrical energy.
• Six common voltage sources are: friction, magnetism, chemicals, light, heat, and pressure.
• Voltage can be used to produce magnetism, chemicals, light, heat, and pressure.
• Magnetism is the most common method used to produce a voltage.
• Chemical cells are the second most common means of producing a voltage.
• A cell contains positive and negative electrodes separated by an electrolytic solution.
• A battery is a combination of two or more cells.
• Cells that cannot be recharged are called primary cells.
• Cells that can be recharged are called secondary cells.
• Dry cells are primary cells.
• Lead-acid batteries and nickel-cadmium (Ni- Cad) cells are examples of secondary cells.
• Cells and batteries can be connected in series, in parallel, or in series-parallel to increase voltage, current, or both.
• When cells or batteries are connected in a series-aiding configuration, the output current remains the same, but the output voltage increases.
IT I1= I2= I3
ET= E1 + E2 + E3
Cells & Battery
Cells & Battery
• When cells or batteries are connected in parallel, the voltage output remains the same but the output current available increases.
IT = I1+ I2+ I3
ET = E1 = E2 = E3
• A series-parallel combination increases both the output voltage and the output current.
• Voltage applied to a circuit is referred to as a voltage rise.
• The energy used by a circuit is referred to as a voltage drop.
• The voltage drop in a circuit equals the voltage rise.
• Two types of ground are earth and electrical.
• Earth grounding is used to prevent electric shock by keeping all appliances and equipment at the same potential.
• Electrical grounding provides a common reference point.
Voltage in Circuits
Voltage in Circuits
Measuring Voltage
Measuring Voltage
What is voltage testing good for?
Voltage testing is very common, you'll use it a lot
Test if your power supply is working, are you getting 5V out of that 7805 regulator?
Verify that your circuit is getting enough power: when all of the blinky lights are on, is the power supply drooping too low?
Verify signals to and from chips to make sure they are what you expect once the circuit is up and running
Testing batteries, solar cells, wall plugs, and power outlets (carefully!) With a current sense resistor you can perform current testing on a project without possibly damaging your meter.
Remember!
You can only test voltage when the ciruit is powered If there is no voltage coming in (power supply) then there will be no voltage in the circuit to test! It must be plugged in (even if it doesn't seem to be working)
Voltage is always measured between two points There is no way to measure voltage with only one probe, it is like trying to check continuity with only one probe. You must have two probes in the circuit. If you are told to test at a point or read the voltage at this or that location what it really means is that you should put the negative (reference, ground, black) probe at ground (which you must determine by a schematic or somewhere else in the instructions) and the positive (red) probe at the point you would like to measure.
If you're getting odd readings, use a reference voltage (even a 9V battery is a reasonable one) to check your voltage readings. Old meter batteries and wonky meters are the bane of your existence but they will eventually strike! Good places to take reference voltages are regulated wall plugs such as those for cell phones. Two meters might also be good :)
Simulation Activity
Simulation Activity
Important Terms
Important Terms
Ampere-hour (A h) rating a common rating for batteries that indicates how much load current a battery can supply during a specified discharge time. For example, a battery with a 100 A h rating can deliver 1 A for 100 h, 2 A for 50 h, 4 A for 25 h, etc.
Battery a device containing a group of individual voltaic cells that provides a constant or steady dc voltage at its output terminals.
Charging the process of reversing the current, and thus the chemical action, in a cell or battery to re-form the electrodes and the electrolyte.
Discharging the process of neutralizing the separated charges on the electrodes of a cell or battery as a result of supplying current to a load resistance.
Fuel cell an electrochemical device that converts hydrogen and oxygen into water and produces electricity. A fuel cell provides a steady dc output voltage that can power motors, lights, or other appliances. Unlike a regular battery, however, a fuel cell has chemicals constantly fl owing into it so it never goes dead.
Hydrometer a device used to check the state of charge of a cell within a lead-acid battery.
Internal resistance, r i the resistance inside a voltage source that limits the amount of current it can deliver to a load.
Open-circuit voltage the voltage across the output terminals of a voltage source when no load is present.
Primary cell a type of voltaic cell that cannot be recharged because the internal chemical reaction to restore the electrodes is not possible.
Secondary cell a type of voltaic cell that can be recharged because the internal chemical reaction to restore the electrodes is possible.
Specific gravity the ratio of the weight of a volume of a substance to that of water.
Storage cell another name for a secondary cell.
Voltaic cell a device that converts chemical energy into electric energy. The output voltage of a voltaic cell depends on the type of elements used for the electrodes and the type of electrolyte.
Self Check
Self Check
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