However, by con- necting a pointer to the coil and adding a scale for the pointer to travel across, you can read the amount of current directly from the scale. Using a higher voltage will result in a greater current flow and "burn out" the lamp, while a lower voltage will not cause enough current flow. The case of a lead-acid cell is made of hard rubber or glass, which pre- vents corrosion and acid leaks. These examples show that, in changing units, the same rules of moving the decimal point apply to both voltage and current.
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Current passing through the coil causes it to act as a magnet with poles being attracted and repelled by those of the horseshoe magnet.
Actually, there are two magnets in this type of meter; one a stationary permanent horseshoe magnet, the other an electromagnet. As long as electrons leave the negative terminal and travel to the positive terminal outside the cell, the electrolyte will carry electrons from the positive plate to the negative plate inside the cell. The shunts may be inside the meter movement and con- trolled by a switching arrangement or they may be external, in which case they are connected in parallel with the meter bind- ing posts.
The most useful of these effects is the development of an electric charge by a photo cell when light strikes the photo-sensitive material in the cell. When the metal balls were removed from one end and rammed into the other end, a flow of these balls was begun in the pipe. A reading one-fourth of the way past the. Meter scale ranges for milliammeters and microammeters, like ammeters, are in multiples of 5 or 10 since these multiples are easily changed to oth- er units.
With this kind of connec- tion the resistance between the end terminals is always the same, and the variable arm provides a contact which can be moved to any position be- tween the end terminals. When the wire has reached its maximum heat, its resistance will stop increasing and the meter reading will remain at a steady value. You will find out that a static charge may transfer from one material to another without friction, but the original source of these static charges is friction.
The term "residual magnetism" is encountered later in this course and in the study of DC generators. There are many types of primary cells used in laboratories and for special ap- plications, but the one which you have used and will be using most often is the dry cell.
Whenever you use an ammeter, the pointer indicates on the meter scale the number of amperes of current flowing, which is also the number of coulombs passing per second. Smaller currents such as 0: Also, volts equals 0. As the negatively charged rod is brought near the uncharged bar, electrons in that portion of the bar nearest the rod would be repelled toward the side opposite the rod.
The voltage will differ on certain types of equipment, but it is usually volts. Fractional values of resistance are expressed in microhms and very large values are expressed in megohms. The case of a lead-acid cell is made of hard rubber or glass, which pre- vents baxic and acid leaks.
Basic Electricity, 1st Edition
The longer the length, the greater the resistance; and the shorter the length, the lower the resistance. The cap for this opening has a vent to allow gas to escape since the cell in operation forms gas at the positive plate.
Electrons in that portion of the rod will be repelled and will move to the opposite end of the bar. Meters used for measuring milliamperes of current are called milliammeters, while meters used for measuring microamperes of current are called microammeters. The unit of current flow is the ampere.
As soon as you connect this across a dry cell, a certain amount of current will flow. When a dry cell supplies electricity, the zinc case and the electrolyte are gradually used up. When these charges exist you have what is called "static" electricity.
Every material has some opposition to current flow, whether large or small, and this opposition is called resis- tance. The milliammeter is a basic meter movement which you will find in various types of meters you will use.
basic electricity by van valkenburg
Without ammeter Ammeter connected in series with line to measure lamp current. The difference in potential between two charges is the electromotive force acting between the charges— commonly called voltage.
Each small ball represents a free electron. Batteries are the main source of power for present-day submarines. How- ever, the wire used in the coil must always be large enough to carry the maximum current of the range the meter is intended for, and therefore changing the wire size would only be practical in the small current ranges, since large wire cannot be used as a moving coil.