A general review of Ohm s law, how to use Ohm s law

1. Pure resistance circuit formula: w q pt uit i rt u t r, in pure resistance circuits (such as incandescent lamps, electric stoves, rice cookers, electric soldering irons, electric blankets, electric irons, motors with rotors jammed, etc.), electric work is equal to electric heat, i.e.

2. Non-pure resistance circuit formula: motor: w e q (uit e i rt); Electrolyzer: W e Q (UIT E Chemistry i RT).

In addition to the conversion of electrical energy into internal energy, part of the electrical energy consumed in non-pure resistance circuits (including electric motors, electric fans, refrigerators, induction cookers, electrolyzers, battery charging, fluorescent lamps, etc.) is converted into mechanical energy (such as electric motors) or chemical energy (such as electrolytic cells), namely:

At this point: w>q(uit>i rt) In a non-pure resistive circuit, u t r can represent neither electrical work nor electric heat, because Ohm's law no longer holds.

1. Ohm's law refers to the fact that in the same circuit, the current through a certain section of conductor is directly proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of this conductor. This law was proposed by the German physicist Georg Simon Ohm in his book "Determination of the Law of Conductivity of Metals" published in April 1826.

2. With the progress of the research on circuits, people gradually realized the importance of Ohm's law, and Ohm's reputation himself has also greatly improved. In honor of Ohm's contribution to electromagnetism, the physics community named the unit of resistance Ohm, which is represented by symbols.

3. When Ohm's law is established, the curve of the sliding beam is called the volt-ampere characteristic curve with the voltage at both ends of the conductor as the abscissa and the current i in the conductor as the ordinate. This is a straight line through the origin of the coordinates, and its slope is the reciprocal of the resistance. Electrical components with this property are called linear elements, and their resistance is called linear resistance or ohmic resistance.

Ohm's law for partial circuits.

The current intensity (i) in a conductor is proportional to the voltage (u) at both ends of the conductor and inversely proportional to the resistance (r) of the conductor itself, i.e., i = u r.

a Some circuits, Ohm's law applies only to linear components and circuits that do not contain electromotive force. The so-called linear element is that the resistance value of the component in the circuit does not change with the voltage at both ends and the current passing through it.

b The current "through", the voltage "at both ends" and the resistance of the "conductor" mentioned in Ohm's law are all for the same conductor.

c i=u r indicates that the current passing through the conductor is directly proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor itself. For r=u i, it must not be assumed that the resistance of the conductor itself will increase with the increase of the voltage at both ends of the conductor and decrease with the increase of the current passing through the conductor, because the resistance is a property of the conductor itself. In fact, a change in u will only cause a change in i.

Ohm's law for closed circuits.

The current i through the closed circuit is directly proportional to the electromotive force of the power supply, and inversely proportional to the sum of the internal resistance of the circuit resistance and the power supply r+r (i.e., the total resistance of the closed circuit), i.e. i = (r+r).

A when the load and the power supply form a closed circuit, there is a current through, the general power supply outside the circuit called the external circuit, the power supply within the circuit called the internal circuit. When an electric current flows through a resistor, electrical energy is converted into thermal energy (internal energy), while when an electric current flows through a power supply, the non-electrostatic action in the power supply converts other forms of energy into electrical energy. So from the law of conservation of energy, we get eidt=i2rdt+i2rdt, so that =ir+ir=i(r+r),i= (r+r).

b The terminal voltage, internal voltage, and electromotive force are both different and related.

When the external resistance r, that is, the external circuit is disconnected, the current is zero, and the internal voltage is zero, then the end-of-circuit voltage is equal to the electromotive force.

r 0, that is, the circuit is short-circuited, the current reaches the maximum value, and the magnitude of the current is i=

r, if the external voltage is zero, then the internal voltage is equal to the electromotive force.

Ohm's law is a very important law in junior high school physics and electricity, which states that the magnitude of the current in a conductor is directly proportional to the voltage of the conductor and inversely proportional to the resistance of the conductor.

The mathematical expression is: i=u r.

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

i, u, r correspondence.

The same conductor or the same section of circuit, different times, different conductors or different sections of the circuit can not be mixed, and the angle code should be added. The units of the three are, in order. a、v

For the same conductor (i.e., r does not change), then i and u

Proportional to the same power supply (i.e. u unchanged), then i

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

It is related to the ratio of u and i, but r is related to the applied voltage u

It has nothing to do with factors such as passing current i.

When the switch is not closed, the voltmeter is connected to both ends of the resistor R2. The ammeter measures the total current and also measures the current flowing through R2.

When the switch is closed, the total resistance decreases (the voltage does not change), so the current increases. If the voltmeter and ammeter are ideal, the voltmeter remains unchanged.

So the answer is A, hopefully.