# URGENT! UNIT 8 practical application questions! 2-4!

Discussion in 'Homework Help' started by JulianXXX18, Sep 22, 2010.

1. ### JulianXXX18 Thread Starter New Member

Sep 22, 2010
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Im having trouble with these practical applications in unit 8. Here is question number 2:

2 resistors are connected in series. one resistor has a resistance of 1000 Ω, and the other resistor value is unknown. the circuit is connected to a 50 volt power supply, and there is a current of 25mA flowing un the circuit. if a 1500Ω resistor is connected in parallel with the unknown resistor, how much current will flow in this circuit?

Feb 17, 2009
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3. ### JulianXXX18 Thread Starter New Member

Sep 22, 2010
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please explain ur equation again. i think im starting to get it.

V = 25mA * 1000 = 25V

so 1 volt = 25 mA? and 25 volts equals 1000 ohms?

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
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You have two resistor connect in series.
First R1 resistor is equal R1 = 1000Ω = 1KΩ second Rx is unknown.
Thous two resistor are connect to 50V power supply.
Total resistance of a circuit is equal
Rtot = 50V/25mA = 2KΩ, and voltage on R1 is equal 25V.
So the remain voltage of the supply voltage must be across Rx.
So Rx = ??

5. ### shteii01 AAC Fanatic!

Feb 19, 2010
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497
You have a circuit with three elements connected in series. These three elements are: 50 V supply, 1k resistor, unknown resistor (RX). Current in this circuit is 25 mA. Since all the elements are in series, 25 mA passes through each element. Therefore:
50V = 25mA(1k+RX)
solve this for RX

6. ### JulianXXX18 Thread Starter New Member

Sep 22, 2010
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so the answer is 25 volts?

7. ### Jony130 AAC Fanatic!

Feb 17, 2009
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Yes 25V will be present across Rx resistor.
So from Ohms Low Rx = 25V/25mA

8. ### shteii01 AAC Fanatic!

Feb 19, 2010
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That was step one. You now know all the elements that make your circuit. Using this information you can find current. You will have 50V supply in series with R1=1k resister in series with combination of RX=1k resister in parallel with 1.5k resistor.

Simplify the two resistors in parallel (RX and 1.5k), that will give you one resistor in series with the R1=1k resistor. Simplify two resistors in series, that will give you one resistor. Use Ohm's Law to find current.