High School Physics Questions, Answer by Title, Thank You, Kirchhoff and Magnetic Pole Questions

The so-called positive and negative is only the actual direction relative to the reference direction, which is positive if it is the same as the reference direction, and negative if it is not. The sum of the current flowing into a node and the current flowing out of the node is zero.

The voltage rise and fall inside the power supply and outside the power supply (external circuit) is opposite to the positive and negative situation taken in the calculation: inside the power supply, the voltage rise (low potential to high potential, i.e., negative to positive) is the positive power supply, that is, it is positive in the calculation; Outside the power supply, the potential of the electrical element decreases along the current direction, and the voltage is negative when calculating; For a single power supply, the internal current flows from a positive to a negative stage (the potential decreases along the current direction according to U=IR), so the positive stage has a higher potential than the negative stage.

Branch: A connecting line containing two or more electrical components between two endpoints.

This point refers to the point where the small magnetic needle is placed, and (ideally, the position corresponding to the center point of the small magnetic needle) is an imaginary curve.

1.The positive and negative values of each current reflect the relationship between the actual direction of the current and the reference direction (whether it is the same or opposite).

It is generally specified that currents with a reference direction diverging from (outflowing) nodes are given a positive sign, while currents with a reference direction pointing (inflowing) to nodes are given a negative sign. This is just a definition, a relative term in which current is a scalar quantity.

2.The external electromotive force is the opposite of the inside! The direction of the current is opposite to the direction of movement of the electrons.

3.Right. Branch: A single circuit element or a series of several circuit elements in series to form a branch of the circuit, and the same current flows through a branch. Each branch of the circuit is called a branch.

4.The direction of the magnetic field should be the direction of a point in the magnetic field, which is the tangent direction of that point or the direction of the n pole pointing when the small magnetic needle is at rest at that place.

5.Magnetic field lines are artificial hypothetical curves, which are curves used to visually depict the distribution of magnetic fields.

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Addendum: The second law above, a few words are missing, and the whole sentence should be:

Potential drop on resistor = potential rise on power supply.

Set the current of each section and the direction of the current to be set, and then use the node formula to flow in equal to the outflow column, and then set a direction for the loop: clockwise or counterclockwise, and then the current you set flows through the resistance potential drop through the power supply from the positive electrode to the negative potential drop, from the negative electrode to the positive potential rise, in a loop, add these potential changes to equal to zero. Note that if you set the direction of the current to be opposite to the direction of the circuit, add a negative sign before the change in the potential of the current flowing.

Finally, the system of equations can be solved.

You can see it when you draw R3 in the middle. i2=-e1/r1+r3=-7/3a

In the same way, i1 = -5 4a

So i3=i2-i1=