# WheatStone bridge

Recently i studied the wheatstone bridge in me physics book in class but i could not understand it properly. I asked the teacher about my confusion but he also dont know. i have posted the picture of topic(wheatstone bridge). My question is ;
1.Why current I1 is following through point A to D in loop ADBA.
2.Why current I2 is following through point D to C in loop DCBD.

My confusion is that why current are following through these two paths. As current always flow through level of a higher potential to a level of lower potential but here it seems opposite.

This is Kirchhoffs law that says the sum of currents into and out of a node is zero .
In the text it makes an assumption of current direction . This is an assumption only , and the directions are all drawn the same for consistency - the actual currents and their directions will come out of the maths . In the Wheatstone bridge example you make think u know the direction of flow, in something more complex you may not - hence the assumption is made that the directions are the same . If you didn’t make this sort of assumption you would get confused with the signs when it came to doing the maths.

Note the line “ assume the currents go anti-clockwise” .

I am quite sure your textbook explains that in order to work the problem, you assume a direction for positive current flow, and if after correctly solving the problem the current value is negative, you simply made the wrong assumption.

I don't think I have ever seen it explained that way before. As current always flow through level of a higher potential to a level of lower potential but here it seems opposite.

If you study physics, electrons flow from negative to positive.

If you study electronics "conventional current" flows from positive to negative. (This is really just a concept that agrees with energy flowing from high to low.)

...When I took electronics in high school, I learned that electrons flow from negative to positive.

When I took electronics in college I learned that current flows from positive to negative.

When I took physics in college I re-learned that electrons flow from negative to positive.

I don't remember when I finally "got it".

Congratulations on having the courage to ask your teacher "why ?". The fact that he/she couldn't explain 'why" does him/her no credit since they obviously didn't understand what they were endeavouring to teach.

DVDdoug:
If you study physics, electrons flow from negative to positive.

If you study electronics "conventional current" flows from positive to negative. (This is really just a concept that agrees with energy flowing from high to low.)

...When I took electronics in high school, I learned that electrons flow from negative to positive.

When I took electronics in college I learned that current flows from positive to negative.

When I took physics in college I re-learned that electrons flow from negative to positive.

I don't remember when I finally "got it".

There is an important caveat - the charges have to be free to move. In a battery they go the other way
because chemical energy is pushing them around against the electric field, same for a generator.

So in a circuit with power sources you find the product of current and voltage is negative for a power
source, representing power being put into the circuit, and positive for dissipating components like wires and
resistors. Assuming you get the signs right(!)

Kirchoff's voltage law is really conservation of energy in disguise. It is only true if there's no change of
magnetic field through the loop, since it doesn't take induction / magnetic energy into account.

Recently i studied the wheatstone bridge in me physics book in class but i could not understand it properly. I asked the teacher about my confusion but he also dont know. i have posted the picture of topic(wheatstone bridge). My question is ;
1.Why current I1 is following through point A to D in loop ADBA.
2.Why current I2 is following through point D to C in loop DCBD.

My confusion is that why current are following through these two paths. As current always flow through level of a higher potential to a level of lower potential but here it seems opposite.

Your confusion is between current in the abstract, which is a signed quantity, and a particular current
whose direction you care about.

The equations in the abstract work whatever the direction, the algebra doesn't know or care. This is
just like many other areas of physics, such as mechanics, where velocities and accelerations for instance
are signed, but the equations are completely general. You just have to be consistent in your sign convention,
the answers are always physically the same.

[ in fact the quantities are often vectors really, but often you can get away with assuming a 1-dimensional world, and a 1-vector is just a signed value. The real full equations are Maxwell's
equations which are vector calculus equations, but unless you are designing antennas or
waveguides you can grossly simplify things ]