14 2 Ohm s Law Case, a problem of Ohm s Law, help solve it.

1. Ohm's Law.

1. The relationship between current and voltage and resistance.

Ask the question: What is the quantitative relationship between current and voltage resistance?

Make a plan and design an experiment: To study the relationship between current and voltage and resistance, the research method used is: control variable method.

That is, keep the resistance unchanged, change the voltage, and study the relationship between the current and the voltage; Keeping the voltage constant, changing the resistance is the study of the current as a function of resistance.

Conduct experiments and collect data information: (will carry out ** design).

Analysis and demonstration: (Analyze experimental data to find the relationship between data, and find out the relationship between physical quantities, which is a common method of physical laws.) ）

It is concluded that the current in the conductor is proportional to the voltage applied to both ends of the conductor when the resistance is constant. With constant voltage, the current in the conductor is inversely proportional to the resistance of the conductor.

2. The content of Ohm's law: the current in the conductor is proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor.

3. The mathematical expression i=u r

4. Description: Applicable conditions: pure resistance circuit (that is, when working with electrical appliances, the electrical energy consumed is completely converted into internal energy).

i, u, r correspond to the same conductor or the same section of the circuit, different times, different conductors or different sections of the circuit can not be mixed, should be added to the angle code to distinguish. The units of the three are A, V, and so on

For the same conductor (i.e., r is constant), then i is directly proportional to u For the same power supply (i.e., u is constant), then i is inversely proportional to r.

It is the definition of resistance, which means that the resistance of a conductor is determined by the length, cross-sectional area, material, temperature, and other factors of the conductor itself.

r u i is a measure of resistance, which indicates that the resistance of a conductor can be given by u i, i.e., r is related to the ratio of u and i, but r is not related to factors such as applied voltage u and passing current i.

5. The basic idea of solving electricity problems.

Carefully review the question and draw the circuit diagram according to the topic; Mark known and unknown quantities on the circuit diagram (add corner codes if necessary);

Choose the appropriate formula or law to solve.

The resistance of the electrical appliance can be found from the voltage and current.

Very well-founded: p=u i

6v 10 ohms.

According to i=u p

3v 10 ohms.

So the resistance of the conductor is 10 ohms. The current passing through this conductor is amperes.

The resistance of a conductor does not increase with the voltage at both ends of the conductor or with the current passing through the conductor.

Resistance r=u i=6

i=（6+3）/r=9/10=

Since the relationship between current and resistance is to be studied, according to Ohm's law, the voltage should be set to a fixed value.

When the resistance becomes larger, the sliding rheostat should be adjusted so that the voltage at both ends of the resistor, that is, the number of the voltmeter, is the same as before the resistor is replaced.

Therefore, the resistance value of the rheostat connected circuit should be increased. So the sliding rheostat should slide to the right. Choose C

It can be seen from the question that the relationship between the current and the resistance is studied, so the voltage at both ends of the resistance should be controlled, and it can be seen from the figure that this is a series circuit, and the current at both ends of the resistance is proportional to the resistance, since the resistance is increased, the voltage at both ends of the resistance will increase. In order to keep the voltage at both ends constant, it is necessary to increase the resistance of the sliding rheostat to keep the voltage at both ends of the constant resistor.

To add) this method is the method of controlling variables

Is the circuit connected to R1 in series with A and then connected to R2 in parallel? If so, the steps are as follows:

30 ohms*, the parallel voltage is equal so ur2=12v, the current flowing through r2 is 12v 1 0 ohm=,i total=

No diagram, no way to start.

Elect d by Ohm's law r=u sullen i

r is a fixed value, which is determined by the conductor itself, and does not change with the bend of you and i.

The answer is definitely wrong to choose DA, and R will not change with the change of voltage.

b , c is wrong, regret is only u i equals r, r is unchanging.

D is right, ditto.