High School Physics Transformer A Why is it wrong

If the secondary coil is connected to the diode, then the positive AC only passes through the diode half the time, and the voltage is 0 half the timeTherefore, the voltage at both ends of R is only half the size of what it would be when the diode is not connected. Naturally, A is wrong.

The diode will make the voltage curve of the secondary coil only half a cycle.

A is right at full cycle, not right now.

Your high school is about the ideal transformer, and if you go to college, the power consumption of the primary coil is really zero.

1. If the power of the secondary coil is zero, it means that there is no load on the secondary side of the transformer, there is no current, according to the principle of power conservation P1 = P2 (this is an important formula, of course, it is only applicable to the ideal transformer stage in high school, in fact, the transformer has its own loss after passing the current in college), that is, the input power is equal to the output power, then the secondary coil power = 0 = primary coil power.

The landlord's confusion is that there is alternating current at the primary level, this is certain, the transformer is dependent on this alternating current to generate magnetic flux, and the primary secondary coil of the transformer induces electromotive force, and the primary induced electromotive force = the connected power supply voltage.

2. The secondary coil is not connected to the load, the circuit is not connected, there is naturally no current, the load circuit is connected, and the current flows through, the landlord said that the load changes the magnetic flux, and the load does change the main magnetic flux after passing the current, but it is offset by the magnetic flux generated by the increased current of the primary coil, so it is still the main magnetic flux generated by the original (this is the reason why the primary current increases with the secondary side).

3. According to Ohm's law r=u i, if the voltage of the secondary coil is unchanged, the resistance becomes larger and the secondary coil current becomes smaller.

The landlord's ambiguity can be discussed.

1.The transformer itself does not consume power.

2.The transformer itself does not produce or consume power, it only transmits power. The secondary load is connected to the load, and the load consumption power is transmitted from the primary.

3.Voltage is the potential energy and current is kinetic energy. In the circuit, no matter how high the voltage is, there is no current, and it will not work. If there is current, there must be voltage, and there is also power consumption.

1. To be precise, the power of the secondary coil is zero, and the primary will not be zero, considering the loss of the excitation part. The primary coil is connected to the power supply, will there be alternating current? There is also a corresponding voltage that will have a magnetic flux.

2. There is only the excitation current without load, the current is very small, and after the secondary load is added, the primary current is composed of the excitation current and the secondary current, and the current will become larger.

3. I didn't understand the third question.

Analysis: Because the wire from the transformer to the user has resistance (set to R line), when the average power consumption of each household increases, the total current of the circuit (set to i total) increases, resulting in the voltage drop on the transmission line (set to U line) to rise, in order to ensure that the voltage at both ends of the electrical appliance is still 220V, so it is necessary to change the turn ratio of the transformer (set to N1:N2) to increase the output voltage (set to U out).

Solution: The original turns ratio is 165:6, and the transformer input voltage is 6600V 6600:U out=165:6

Namely. U out = 240V

U line = 240-220 = 20V

From the known total power of the original electrical appliances is 100 * 440 = 44000W, then I total = w total U = 44000 220 = 200a R line = U line i total = Europe.

After the average power consumption per household is 250W:

The total power of electrical appliances is 250 * 440 = 11000 wi total '= w total' u amount = 110000 220 = 500a u line ' = i total ' * r line = 50v

U out' = 220 + 50 = 270V

n1:n2=6600:270=200:9 (to solve this kind of problem, pay attention to understanding the relationship between invariants and variables, and use formulas appropriately).

Analysis: Because the wire from the transformer to the user has resistance (set to R line), when the average power consumption of each household increases, the total rolling current of the circuit (set to i total) increases, resulting in the voltage drop on the transmission line (set to U line) to rise, in order to ensure that the voltage at both ends of the electrical appliance is still 220V, so it is necessary to change the turns ratio of the transformer (set to N1:N2) to increase the output voltage (set to U out).

Solution: The original turns ratio is 165:6, and the transformer input voltage is 6600V 6600:U out=165:6

Namely. U out = 240V

U line = 240-220 = 20V

From the known total power of the original electrical appliances is 100 * 440 = 44000W, then I total = w total U = 44000 220 = 200a R line = U line i total = Europe.

After the average power consumption per household is 250W:

The total power of electrical appliances is 250 * 440 = 11000 wi total '= w total' u amount = 110000 220 = 500au line chang' =

i total '*r line = 50v

Resistant to rent. U out' = 220 + 50 = 270V

n1:n2=6600：270=200：9

To solve this kind of problem, we should pay attention to understanding the relationship between invariants and variables, and use formulas appropriately).