i need help with resistance?

Question

Resistance problem?
the total power consumed by two resistors , connected in a parallel is 25 watts .if the voltage applied is 5 volts dc and the current in one resistor is 1.5 ampere ,what are the resistances of the two resistors?


please show how you get the two resistances,thanks

Answer 1

P=IV

25=5I
==> I=5
if total resistance is 5 and the resistors are in parallel, we
have a current divider

if the current through R1 is 1.5, then the current through R2=3.5

and (R2/(R1+R2))*5=1.5
==> .3R1+.3R2=R2
.3R1=.7R2

now I^2(R1R2/(R1+R2)=25 I=5

so
R1R2/(R1+R2)=1

With some manipulating R2=10/7 and R1=10/3

So R1+R2=100/21

Check
the parallel resistance is 1
V^2/R=25/1=25 watts.

Answer 2

Fisrt, since we have two resistors in parallel, we know the votage across each will be the same, 5 volts. Label one R1 and the other R2. We also know that the total power dissipated will equal 25 watts, the sum of the individual powers dissipated by each resistor. We can use the equation: P(total) = P(R1) + P(R2). Substituting Known quantities: 25w = P(R1) + P(R2).

We can find the power of one resistor, since we know the current through it, and the voltage across it, using the equation: P = I x E. P = 1.5amps x 5 volts = 7.5 watts. Lets call this R1, so substituting into the above equation:
25w = 7.5 watts - P(R2). Solve for P(R2) and we get 17.5 watts for R2.

Using: P = I x E, we find the current through R2 by re-arranging the equation and solving for I, which gives us
17.5 watts / 5 volts = 3.5 amps. Now using Ohm's law:

R2 = 5 volts / 3.5 amps = 1.429 ohms. Likewise, we can find
R1 the same way: R1 = 5 volts / 1.5 amps = 3.333 ohms.

To check the answer, R1 // R2 = 1 / ( (1/1.429) +(1/3.333) ) = 1.00 ohms. Using the power equation: P = ( I1 + I2) x E =
(3.2 amps + 1.5 amps) x 5 volts = 25 watts; The power equation V*/ R works too: 5*/1 = 25/1 = 25 watts.

There are other ways to solve this problem and give you the same results, but I thought this method would give you the best insight into solving the problem and understanding the process. Hope this helps you out!

Answer 3

Watts = volts x current
25 = 5 x current
current = 5 amps

The total current in the circuit is 5 amps.

The current in one resistor is 1.5 amps

Total current = the sum of the current in both resistors (since they are in parallel).

So the current in the other resistor = 5 -1.5 = 2.5

Ohms law Resistance = voltage / current

resistor A = 5 / 1.5 = 3.3333 ohms
resistor B = 5 / 2.5 = 2 ohms

Answer 4

1) Ohm's Law V = I*R

so, R = V/I R1 = 5/1.5

2) P = VI

Substituting 1 into 2 gives P = V^2/ Rtotal

So Rtotal = V^2/P

And you already know Ra, so use the parallel resistance rule to find R2 given R total and R1

Answer 5

First find total current, by dividing total watts by total voltage.
25W/5V = 5A
One resistor was given at having 1.5A flow.
To find resistance of this resistor we simply divide voltage by current.
5V/1.5A = 3.33ohm

The other resistor must have the other 3.5A flowing, so...
5V/3.5A = 1.43ohm

The answer is 3.33ohms and 1.43ohms.