Fuses, resistors and potentiometers are not 'polarized' (current can flow through them either way). The battery, however, has a positive terminal and a negative terminal.
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A 'storage cell' can be recharged repeatedly. A 'primary cell', such as a common Zinc-Carbon flashlight cell, can only be used once.
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The 'conventional' Zinc-Carbon or Alkaline flashlight battery CANNOT be recharged while a 'storage cell' like a car battery can be recharged numerous times.
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An ideal battery would supply precisely the same voltage regardless of the current drawn. Real-life batteries exhibit 'internal resistance' which causes a drop in voltage when current is drawn. Ever noticed the headlights dim when the starter is cranked on a cold winter day ?
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The 'conventional' Zinc-Carbon or Alkaline flashlight battery CANNOT be recharged while a 'storage cell' like a car battery can be recharged numerous times.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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One important specification of rechargeable batteries is the 'capacity' expressed in milliampere-hour (or ampere-hour), a certain amount of current that can be delivered for a given period of time (typically, 20 hours). Exceeding the capacity reduces operating time, the battery is depleted more rapidly.
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key word: VOLTAGE. Adding cells in series brings up the available voltage. However, the total current available from the string remains limited to what a single cell can supply.
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The last band in a resistor's colour code identifies 'tolerance': an allowed variance in percentage from the nominal value. For example, a GOLD band means 5%.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The last band in a resistor's colour code identifies 'tolerance': an allowed variance in percentage from the nominal value. For example, a GOLD band means 5%.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Key words: ACCURATE and PREDICTABLE. The smallest possible "tolerance" will ensure that the actual value of the resistors fall within a narrow range of their nominal values.
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Key words: NOT CRITICAL. A wide tolerance is amply acceptable when the actual value of the resistor is not critical. The extra cost of a precision resistor is not needed.
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The first two bands are significant digits, the third band is a multiplier. The fourth band is tolerance. In this example, both first bands read '1', both second bands read '2'. The third band multiplies by 10 or 100 as the case may be.
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The first two bands are significant digits, the third band is a multiplier. The fourth band is tolerance. In this example, the first two digits are '27' and the multiplier adds four zeroes (or multiplies by 10 000). Result = 270 000 ohms or 270 kilohms.
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Milli is a thousandth. A thousand milliamperes is one ampere. Converting from milliamperes to amperes: from small units to larger units, requires fewer digits, decimal point moves to the left by three positions, a thousand times less.
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Milli is a thousandth. A thousand millivolts is one volt. Converting from millivolts to volts: from small units to larger units, requires fewer digits, decimal point moves to the left by three positions, a thousand times less.
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Kilohm is a thousand ohms. Converting from kilohm to ohms: from large units to smaller units, requires more digits, decimal point moves to the right by three positions, a thousand times more.
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Kilovolt is a thousand volts. Converting from kilovolts to volts: from large units to smaller units, requires more digits, decimal point moves to the right by three positions, a thousand times more.
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One quarter ampere is 0.25 amperes. Milli is one thousandth. One ampere is a thousand milliamperes. Converting from ampere to milliampere: from large units to smaller units, requires more digits, decimal point moves to the right by three positions, a thousand times more.
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A millivolt is a thousandth of a volt. A volt is one thousand millivolts. Converting from volts to millivolts: from large units to smaller units, requires more digits, decimal point moves to the right by three positions, a thousand times more.
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Wood, paper and mica do NOT conduct electricity. The best conductors, in descending order, are: Silver, Copper, Gold and Aluminum.
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Power is voltage times current, P = E * I. When current flows through a resistor, a 'voltage drop' ensues. Volts times amperes become watts. Power is dissipated as heat.
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The best conductors, in descending order, are: Silver, Copper, Gold and Aluminum. Carbon is a poor conductor, it is used to fabricate resistors. Silicon is used to make 'semiconductors'.
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As the name implies, a 'conductor' readily passes electrical current. An Insulator ( synonym = dielectric ) does not let current flow. A resistor conducts but badly.
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Reciprocal = 'the inverse of something'. 1 over resistance yields CONDUCTANCE. Low resistance implies high conductance. High resistance implies little conductance.
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As current flows through electronic components, some voltage is 'lost'. Remember voltage as 'pressure', there is more 'pressure' before a resistor than after it: this represents a 'voltage drop'.
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'Open' circuit = no current ( a loop from one side of the voltage source to the other side does NOT exist, the loop is open ). 'Closed' circuit = current ( a path exists from one side of the voltage source to the other side, current flows, the loop is closed ). 'Short circuit' = heavy current ( a very low resistance path exists between from one side of the voltage source to the other side, large current ensues ).
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'Open' circuit = no current ( a loop from one side of the voltage source to the other side does NOT exist, the loop is open ). 'Closed' circuit = current ( a path exists from one side of the voltage source to the other side, current flows, the loop is closed ). 'Short circuit' = heavy current ( a very low resistance path exists between from one side of the voltage source to the other side, large current ensues ).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Frequency is the number of cycles per second of an Alternating Current (AC). Frequency is expressed in hertz (Hz). One hertz is one cycle per second.
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Hz = hertz = cycles per second. Frequencies audible to humans range from 20 Hz to 20 000 Hz. Speech frequencies important for intelligibility in communications range from 300 Hz to 3000 Hz.
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Hz = hertz = cycles per second. Frequencies audible to humans range from 20 Hz to 20 000 Hz. Speech frequencies important for intelligibility in communications range from 300 Hz to 3000 Hz.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Hz = hertz = cycles per second. Frequency is the number of cycles per second of an Alternating Current (AC). Frequency is expressed in hertz (Hz). One hertz is one cycle per second.
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100 Hz = 100 hertz = 100 cycles per second. The duration of ONE cycle, the "period", is 1 / frequency. In this example, 1 / 100 Hz yields 0.01 second.
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One cycle in 0.1 second, how many cycles in a second ? The duration of ONE cycle, the "period", and frequency have an inverse relation: Frequency is 1 / period. In this example, 1 / 0.1 second yields 10 hertz.
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'Harmonics' are integer MULTIPLES (e.g., 2x, 3x, 4x, 5x,...) of a given frequency. The base frequency is referred to as the 'fundamental'.
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key word: VOLTMETER. An instrument to measure voltage. The voltmeter is always connected in parallel to measure a difference of potential between two points, across a component, etc.
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key word: AMMETER. Ammeter comes from the words ampere + meter, it is used to measure current. Current flows THROUGH a circuit. The circuit must be 'broken' and the ammeter inserted in series with the circuit to measure current. Ammeters have very low resistance and, thus, have little effect once inserted in the circuit.
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This is a bit of a catch. A PERFECT conductor would exhibit ZERO resistance. An ammeter actually has a very low resistance. [ For example, a 10 A ammeter can have a resistance of 0.005 ohms, a 1 A ammeter can have 0.05 ohms and a 500 mA ammeter can introduce 0.2 ohms of resistance in the circuit. ]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Ammeter comes from the words ampere + meter, it is used to measure current. Current flows THROUGH a circuit. The circuit must be 'broken' and the ammeter inserted in series with the circuit to measure current. Ammeters have very low resistance and, thus, have little effect once inserted in the circuit.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Ammeter comes from the words ampere + meter, it is used to measure current. Current flow THROUGH a circuit. The circuit must be 'broken' and the ammeter inserted in series with the circuit to measure current. Ammeters have very low resistance and, thus, have little effect once inserted in the circuit.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The voltmeter is always connected in parallel to measure a difference of potential between two points, across a component, etc. Ammeter comes from the words Ampere + meter, it is used to measure current. Current flow THROUGH a circuit. The circuit must be 'broken' and the ammeter inserted in series with the circuit to measure current. Ammeters have very low resistance and, thus, have little effect once inserted in the circuit.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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