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Physics problems: electricity

 

 

Problem 78.

What is the equivalent resistance between points A and B?

current

Solution

 

To find the current through the battery, we need to find the equivalent resistance of the circuit. With the known equivalent resistance of the circuit, the current is

charge

Thus the first step is to find the equivalent resistance of the circuit.

We can clearly see (figure below) that two 20 ohm resistors are connected in parallel (red line), two 10 ohm resistors are connected in series (green line), three 20 ohm resistors are connected in series (blue line).

voltage

 

We can find the corresponding equivalent resistances:
- two 20 ohm resistors connected in parallel:

electric field

voltage

- two 10 ohm resistors connected in series:

electron

- three 20 ohm resistors connected in series:

electric current

Now we have a circuit shown in the figure below. In this circuit two 10 ohm resistors are connected in series. We replace them with an equivalent resistor with the resistance of

flux

 

mass

 

 

Now we have two 20 ohm resistors connected in parallel (see figure below). We replace them with in an equivalent resistance of

current

magnetic field

 

potential

 

In the equivalent circuit we have two 10 ohm resistors connected in series (see figure below). We replace them with an equivalent resistance of

Ohm's law

 

current

 

Finally we have 20 ohm and 60 ohm resistors connected in parallel (see figure below), which can be replaced with an equivalent resistance of

electirc potential

energy

electric


Then two resistors (30 ohm and 15 ohm) are connected in series. Their equivalent resistance, which is equivalent resistance of the whole circuit, is

mass

Now we can find the current through the battery, which is

conservation law

 

 

 

 

 

 

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