1 DC ELECTRICAL CIRCUITS RESISTANCE. 2 DC ELECTRICAL CIRCUITS In short resistance limits the flow of current. Resistance is measured in ohms, the symbol

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DC ELECTRICAL CIRCUITS

RESISTANCE

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In short resistance limits the flow of current.

Resistance is measured in ohms, the symbol used to refer to resistance is the omega symbol Ω.

The letter R is used to represent resistance when working with formulas.

The resistivity of material determines the overall resistance, however there are three other factors that determine resistance.

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There are three factors that contribute to a material’s resistance, typically cable.

LENGTH

CROSS SECTIONAL AREA

TEMPERATURE

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Resistors are commonly used to perform two functions in a circuit.The first use is to limit the flow of current in a circuit.

I = E / RI = 15 V / 30 ΩI = 0.5 A

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The second use is to produce a voltage divider.

A to B = 1.5 VA to C = 7.5 V A to D = 17.5 VB to C = 6 VB to D = 16 VC to D = 10 V

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DC ELECTRICAL CIRCUITSDC ELECTRICAL CIRCUITS

Fixed resistors have only one ohmic value, which cannot be changed or adjusted. One type of fixed resistor is the composition carbon resistor.

Fixed resistors have only one ohmic value, which cannot be changed or adjusted. One type of fixed resistor is the composition carbon resistor.

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Carbon resistors are very popular for most applications because they are inexpensive and readily available in standard sizes and wattages.

Carbon resistors are very popular for most applications because they are inexpensive and readily available in standard sizes and wattages.

½ Watt 1 Watt 2 Watt

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Metal Film resistors are another type of fixed resistor. These resistors are superior to carbon resistors because their ohmic value does not change with age and they have improved tolerance.

Metal Film resistors are another type of fixed resistor. These resistors are superior to carbon resistors because their ohmic value does not change with age and they have improved tolerance.

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Wire wound resistors are fixed resistors that are made by winding a piece of resistive wire around a ceramic core. These are used when a high power rating is required.

Wire wound resistors are fixed resistors that are made by winding a piece of resistive wire around a ceramic core. These are used when a high power rating is required.

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The resistor color code can be used to determine the resistor’s ohmic value and tolerance.The resistor color code can be used to determine the resistor’s ohmic value and tolerance.

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Exceeding the power rating causes damage to a resistor.Exceeding the power rating causes damage to a resistor.

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Variable resistors can change their value over a specific range. A potentiometer is a variable resistor with three terminals. A rheostat has only two terminals.

Variable resistors can change their value over a specific range. A potentiometer is a variable resistor with three terminals. A rheostat has only two terminals.

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Schematic symbols are used to represent various types of fixed resistors.Schematic symbols are used to represent various types of fixed resistors.

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This resistor would equal 1-2 and 2 (0s) or 1200Ω with a tolerance of + 20%.

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1 2 X 100

+ 20%

12 X 100 = 1200Ω + 20%

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What is the color code of a 280 ohm resistor ?

REDGRAYBLACK

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A resistor’s tolerance is the amount a resistor may vary and still be acceptable.

The larger the tolerance of a resistor the cheaper the resistor is.

Resistors of + 10% are widely accepted for use in electronic circuits.

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1000 ohm resistor has a color code of?

2.2 k ohm resistor color code?

45 ohm color code?

12.5 k ohm color code?

1 ohm color code?

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The formula for finding total resistance in a series circuit is Rt = R1 + R2 + R3 + Rn,

(Rn is any number or resistances in series).

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To find total resistance in a parallel circuit the formula is:

This is called the reciprocal formula and used for 3 or more resistors in parallel, it can be used for 2 resistors in parallel however there is another simpler formula for finding 2 resistor in parallel.

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The total resistance of a parallel circuit will always be less than the lowest branch.

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To find Rt in a series parallel circuit we have to add the resistor to the branch circuit its in then use the reciprocal formula again.

WE ALREADY DETERMINED THE VALUE OF THE PARALLEL RESISTANCES FOR THIS CIRCUIT, IT IS 23.46 OHMS, IN THIS CASE WE WOULD SIMPLY ADD THE 37 OHM RESISTOR TO THE TOTAL SO IT WOULD EQUAL 60.46 OHMS

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If the series resistor is at the end it gets added to the R3 resistor than we would apply the reciprocal formula again, in this case Rt will be different from the previous totals.

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To find total resistance in a parallel circuit with resistors that all have the same value we can use the simplified formula:

R (resistance) = value of one like resistor (R) divide by the number of like resistors (N).

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What would 4, 100 ohm resistors in parallel equal?

What would 6, 120 ohm resistor in parallel equal?

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To find two resistor in parallel you can use the product over sum method.

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1 DC ELECTRICAL CIRCUITS RESISTANCE. 2 DC ELECTRICAL CIRCUITS In short resistance limits the flow of current. Resistance is measured in ohms, the symbol