Calculate the resistance of a second resistor, connected in series that reduces the current to 5.00 A.?

Question

When a resistor is connected to a 25.0 V power supply, the current through the resistor is 12.5 A. Calculate the resistance of a second resistor, connected in series that reduces the current to 5.00 A. Can anyone help me get the answer, with calculations too?

Answer 1

V=IR so R must be 2 Ohm

add second R

25=5 (2+3) so 2nd R must be 3

Answer 2

capacitance and resistance  just add them up 12.5+5.00=17.5...........tom

Answer 3

I'm not sure where Tholeeder got sidetracked,*

but the first post by "jsbrads" is correct (just not totally clear if the person doesn't already understand how these things work.)

*[ You do NOT just add up 12.5 amperes and 5 amperes to produce anything.  They are not the series resistances, but currents.  12.5 was the original current.  5.0 is the final desired current.]

The question asked for a series resistance, and you *can* add up resistances that are placed in series.  

If you want 5 amps from a 25 volt source, by Ohm's law, ( R=V/I where V is in volts and I is current in amps) it is simply 25 volts divided by 5 amps, yielding 5 ohms needed.

(You may also see Ohm's law written  R=E/I in older books.  This is the same thing, but E stands for Electromotive force which is an old name for Volts)

Since you already have a 2 ohm resister ( because 25 volts / 12.5 amps = 2 ohms ), you need another three to give the total needed value of 5.

Example of series:

(+25volts) ------\/\/\ 2 \/\/\-----\/\/\ 3 \/\/\------ (negative terminal of supply)

. . . . current flow = 5 amperes

Answer 4

'''Original Circuit""

Supply Voltage = 25 Volts

Supply Current = 12.5 Amps

Formula:

Voltage / Current = Ohms

25 / 12.5 = 2

Original Resistor = 2 Ohms

'''Calculated Second Resistance'''

New Parameters:

Circuit Current = 5 Amps

Second Resistance in series with original resistance.

Formula:

Voltage / Current = Ohms

25 / 5 = 5

Total Resistance - Original Resistor = Second Resistance

5 Ohms - 2 Ohms = 3 Ohms

Second Resistance = 3 Ohms

: )

Answer 5

using the formula V=IR

where V=25V as voltage is the same in parallel

I=5A

from equation R=V/I

=25/5=5 ohm