Now I need 10 questions about physical electric power in grade two, Better not be a textbook~

Now I need 10 questions about physical electric power in grade two, Better not be a textbook~

1. The daily power consumption of a refrigerator is 1.2 kwh. Under normal circumstances, the compressor works for 5 hours a day and night. What is the power of the refrigerator? What is the current in the working process?
Answer: P = w / T = 1.2kwh/5h = 0.24kw = 240W
From P = IU, I = P / u = 240W / 220V = 1.1a
2. When an electrical appliance with a resistance value of 60 Ω works normally, the voltage at both ends is 110 v. in order to make it work normally on the 220 V power supply in the home circuit, and there is only one resistor of 240 Ω and one resistor of 80 Ω at hand, how to connect the circuit?
Answer: the normal working current is 110 / 60 = 11 / 6A
The resistance connected in the 220 V circuit should be 220 V / (11 / 6A) = 120 Ω
After two resistors are connected in parallel, the resistance is 1 / (1 / 80 + 1 / 240) = 60 Ω
Then it is connected in series with the electric appliance in the circuit, and the total resistance is 60 + 60 = 120 Ω
3. A microwave oven works at 100% power for 5 minutes, and then works at 50% power for 5 minutes. It takes 7 * 10 quintic J energy to cook a pot of rice. Assuming that all the power consumed by the microwave oven is absorbed by rice, and the 100% power of the microwave oven is 1000W, how long does the microwave oven work? (accurate to seconds)
Answer: a total of 1000j / s * (300s + 300s * 0.5) = 450000j was consumed in the first 10 minutes
Less than 700000j. If it works for another 10 minutes, the power consumption will reach 450000 + 1000 * 300j
=750000j > 700000j, so working (700000-450000) J / (1000j / s) = 250s = 4min10s. The total working time is 14 minutes and 10 seconds
4. The electric power consumed by the rechargeable battery during charging is 9W, of which 20% is converted into the chemical energy of the battery, while the electric power provided by the rechargeable battery during use is 0.4W, and the efficiency of chemical energy converted into electric energy of the battery is 80%. How long can the battery be used after charging for one hour?
Answer: charge for one hour, electric energy is 9j / s * 3600s * 20% = 6480j
Because the chemical energy conversion efficiency is 80%, the chemical energy consumption rate is 0.5j/s
So it can be used 6480 / (0.5j / s) = 12960s = 3.6h
5. A certain type of rechargeable battery is marked with "3.6V 1200Ma * H". A small radio with rated power of 0.5W uses this type of battery to supply power. How long can the battery make the small radio work?
The answer is: the energy stored in the battery is 3600j * 526s
Working time t = 15552j / (0.5j / s) = 31104s = 8.64h
6. A lamp needs to be connected temporarily during the construction. Because the power supply is far away from the construction site, the wire is long. When the white flag lamp marked with "220 V 200 W" is connected, it is found that the lamp cannot light normally. According to the measurement, the voltage at both ends of the lamp is 200 V, and the power supply voltage is stable and equal to 220 v
(1) What is the resistance of the wire?
(2) What is the voltage at both ends of the white flag lamp marked with "220 V 40 W"?
Answer: 1. The resistance of "220 V 200 W" white flag lamp is 220 ^ 2 / 200 = 242
The current in the actual circuit is: 200 / 242 = 0.826
The voltage distributed on the conductor is 220-200 = 20V
The resistance of the wire is 20 / 0.826 = 24.2 ohm
2. The resistance of "220 V 40 W" white flag lamp is 220 ^ 2 / 40 = 1210
The total resistance in the actual circuit is 1210 + 24.2 = 1234.2
The current of the circuit is 220 / 1234.2 = 0.178a
The voltage at both ends of D lamp is 0.178 * 1210 = 215v
How to measure electric power with ammeter and voltmeter
Answer: in a circuit, connect a small bulb, the ammeter and the small bulb are connected in series, the voltmeter and the small bulb are connected in parallel, close the switch, read out the voltage and current at this time, and get the power of the small bulb from the formula P = UI
8. When a motor works normally, the coil resistance is 20 Ω, the working voltage is 380 V, and the current in the coil is 1.5 A. what is the input power, heating power and efficiency of the motor?
Answer: input power is 380 times 1.5 equals 570 watts. Heating power is 1.5 times the square of 20 equals 45 watts. Efficiency is (570-45) / 570, equals 92.1%
9 if the output voltage of the power plant is 3300v, the power transmitted is 3300kW, and the power of the transmission line is 2 Ω, what is the resistance heating power and the loss rate?
Answer: first, the current is 3300000 / 3300 = = 1000A, so the heating power is 1000 square multiplied by 2, which equals 2000kW. The loss rate is 2000 / 3300 = = 60.61%
10. The output power of the power plant is P1, which is transmitted by voltage u, and the line loss power is p. if u is increased by N times, the line loss power is p
Answer: u is increased by N times, and the current is reduced to 1 / N of the original
If the loss power is equal to I ^ 2 * r, the loss power becomes 1 / N ^ 2 of the original
Who knows about all the formulas of electric power, electric work, etc. in the second grade of junior high school
I = u / r u = IR r = u / I P = w / T P = UI P = u ^ / R P = I ^ R q = uitphysical quantity physical formula current definition I = q / T Ohm's law I = u / R series circuit I = I1 = I2 parallel circuit I = I1 + I2 voltage series circuit u = U1 + U2 parallel circuit u = U1 = U2 resistance series connection r total = R1 + R2 parallel connection r total = r1r2 / (R1 + R
P stands for electric power in watts
W is the unit of electrical work in joules
T is the unit of time in seconds
U is the voltage in volts
I stands for current in ampere
R stands for resistance in ohm
P=W/T
W=PT
P=UI
P=IIR
P=UU/R
W=UIT
My electric car battery changed from 60V to 72V. How can I maintain it
The maintenance of your motor should be the same as before
The influence of short circuit (open circuit) at the output of ideal voltage source and voltage source and ideal current source and current source on power supply
The ideal voltage source has constant output voltage, but it will produce infinite current when it is short circuited
The ideal current source has constant output current when it is short circuited, but it will produce infinite voltage when it is open circuited
The ideal power supply only exists in theory. In the real electronic technology, it has similar ideal characteristics only in a small range (a few volts or a few milliamps). They can not produce infinite voltage or current
Which properties of metals determine the resistivity of metals? For example, silver, copper and aluminum have low resistivity
Why does metal material have a great influence on resistivity?
The arrangement of atoms in metal. Metal belongs to crystal structure, in which there are regularly arranged atoms and free moving electrons. When the electrons are in the atomic gap, when the voltage is applied to the metal, the electrons doing free work begin to move in a directional direction. The more complex the arrangement of atoms, the greater the obstruction to the electrons, the greater the resistivity
72V electric car battery, there are six series, how many degrees do you need to charge?
It's like 20 Ann,
1. All kinds of efficiency are 100%,
2. Standard 0.1C charging mode is adopted,
3. The battery is completely discharged before charging
Charging voltage: u = 72V
Charging current: I = 20 / 10 = 2A
Charging time: T = 10h
The charging power is: P = IU = 2 × 72 = 144 (W),
The total power consumption is: a = Pt = 144 × 10 = 1440 (WH) = 1.44kwh = 1.44kwh
That is: the power consumption of each charging is 1.44 degrees
Considering that the total efficiency can not be 100%, the assumption is 85%:
1.44 △ 85% ≈ 1.69 (degree) doesn't use much electricity, which is much more cost-effective than oil-burning motorcycle
Full charge and discharge, about 1.5 degrees
Look at the wattage of the charger. If it's 200 watts, two kilowatts in 10 hours. (charging time of electric vehicle is generally 6-10 hours)
1) In the short circuit state, the short circuit current is very large, and the terminal voltage of the power supply is also very large, right? 2) in the open circuit state, the terminal voltage of the power supply is not necessarily the maximum, right
In short-circuit state, the short-circuit current is very large, and the terminal voltage of the power supply is also very large, which is wrong. The power supply voltage will be reduced due to the short circuit
In the open circuit state, the terminal voltage of the power supply is not necessarily the maximum, which is wrong. In the open circuit state, the current is zero and the terminal voltage is the maximum
In the four probe method, is the block resistance the surface resistivity? Can the four probe method be used to directly test the surface resistivity of thin films?
If yes, is it the value read directly? Is there any other calculation formula? What is the formula?
Block resistance is surface resistivity
The surface resistivity of thin films can be measured directly by four probe method
Calculation formula: block resistance (or surface resistivity) r = 4.532 * V / I, where V is the potential difference between probes 2-3 and I is the current between probes 1-4
Yes, the square resistance is the surface resistance of the film, which can be directly measured? If it is surface resistance, how to calculate the surface resistivity based on it? Is there a formula? thank you.
How far can Emma's 48V 20Ah 500W electric motor run? Can it run far by raising the battery voltage to 60V or 64V?
It's less than 3 months since I bought it. If I use the original charger, it will be dead within 30 km. After changing the charger, it will be no more than 45 km at most
48V 20Ah 500W motor can run about 50km. Of course, the distance depends on your brake, weather temperature, etc. it is not feasible to increase the voltage to 60V or 64V, because your motor controller and charger are 48V. If you change to 60V, your cost will be increased. The motors, controllers and chargers mentioned above need to be replaced
The bulb marked 12 V 8 W is connected in series with a resistor and connected to a 12 V power supply. If the power consumed by the resistor is 1 W, what is the power consumed at this time
Four bulb options a, the total power consumed by bulb and resistor is 9 watts, B the total power consumed by bulb and resistor is 8 watts, C the total power consumed by bulb is more than 7 watts, d the total power consumed by bulb is less than 7 watts
Choose D, the power consumption of the bulb is less than 7W
Because this bulb consumes 8W when it is connected to 12V, after a resistor is connected in series, the total power consumed must be less than 8W: according to P = u ^ 2 / R, when the voltage is constant, the total resistance increases and the power decreases
Now the resistance has consumed 1W, of course, the power of the bulb is less than 7W