Calculate Current Through R3: Negative Possible?

[Sastronaut]

Homework Statement

Calculate the current through R3.

Homework Equations

V=IR

The Attempt at a Solution

my attempt is attached. My question revolves around my answer...is a negative current a legitimate answer? What does it mean?

 

[lewando]

It is a legitimate answer provided you show a direction arrow (which you have done). It means that the current is not traveling in the direction indicated by your direction arrow. It is going in the opposite direction.

 

[lewando]

Looking at your loop equations, they seem a bit suspect. If you are summing the changes in voltage across each element along a loop, equating the sum to zero, you should get something different.

 

[ehild]

Homework Statement

Calculate the current through R3.

Homework Equations

V=IR

The Attempt at a Solution

my attempt is attached. My question revolves around my answer...is a negative current a legitimate answer? What does it mean?

Your equations 1 and 2 are wrong. Note, that the potential decreases in the direction of the current.

ehild

 

[Sastronaut]

What should my equation for loop 1 be?

 

[ehild]

You start at the negative pole of the battery, and follow the change of potential in the direction, indicated by the green arrow. The potential increases by 5 V traversing the battery. Then it decreases by I₃R₃ along R₃. Then again, it decreases by R₁I₁, when you return to your initial position. The net change of potential is zero: 5-I₃R₃-I₁R₁=0.
Do the same for the other loop. Note that going in direction opposite to the current, the potential would increase.

ehild

 

[Sastronaut]

okay I think I am following you so for loop 2 the equation is then -10V+I3R3+I2R2=0?

 

[ehild]

okay I think I am following you so for loop 2 the equation is then -10V+I3R3+I2R2=0?

Yes.

ehild