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Two parts x is equal to seven parts 13, how to calculate, write the formula for points
x/2=13/7
x=2*13/7=26/7
1 Division [28 - (3 / 8) division (5 / 6-1 / 3)] formula
1/{28-(3/8)/[(5/6)-(1/3)]}
=1/{28-(3/8)/[(5/6)-(2/6)]}
=1/[28-(3/8)/(1/2)]
= 1/(28-3/4)
=1/[(28*4-3)/4]
=1/(109/4)
=4/109
The circuit voltage is 41v, r = 20 Ω, D is DC motor, its coil resistance is 1 Ω, the motor works normally, and the reading of voltmeter is 21V
(1) Through the current in motor D
(2) Input power of motor
(3) The power that a motor converts into mechanical energy
(4) Total power of power supply
The voltmeter is connected to both sides of the motor
(1)(41-21)/20=1A
(2) 1*21=21w
(3) 21-1^2 *1=20
(4)41*1=41
How to do 78 × 32 + 67 × 32 + 78?
78 × 32 + 67 × 32 + 78
= （78 + 67）× 32 + 78
= 145 × 32 + 78
= 145 × 2 × 16 + 78
= 290 × 16 + 78
= 4640 + 78
= 4640 + 80 - 2
= 4720 - 2
= 4718
The team answers for you
How do batteries convert chemical energy into electrical energy
In chemical substances, some (usually the outermost) unstable electrons move directionally due to the external potential difference, forming a current. At this time, the work done by the electrons leaving the nucleus is the consumption of chemical energy, and the work done by the formed current in the circuit is electrical energy. (as for the TV difference, this is the difference in the potential formed by the different structures of the substances themselves.)
How to solve X / 240 + X / 80 = 40?
Multiply the equal sign by 240 to get x + 3x = 9600
X=2400
What kind of fruit and metal sheet are used to make the fruit battery with the highest voltage? Which of the two metal sheets is the positive pole and which is the negative pole?
It's best to make a table. The more information you give, the more points you add
First, rotate all the lemons, one at a time. Squeeze them by hand while rotating until they feel a little "soft". This is to make more juice inside the lemons. This step is very important, because it can help you get the best effect of the lemon battery
Screw a galvanized screw into about 1 / 3 of a lemon. With a knife, carefully cut a 1cm incision in the other 1 / 3 of the lemon
Note: it is best for adults to use the knife. In any case, please use the knife "carefully" and "slowly"
Insert the copper coin into the cut until half of the coin is in the lemon
Note: make sure you are using a new coin with luster. If the coin is old and has no luster, polish it with Briggs
Believe it or not, you can get current from lemon now! Like other batteries, coin is its positive (+) and screw is its negative (-). Unfortunately, this battery is very weak. But if you have several such batteries, you can connect them together to form a lemon battery pack
Insert the coin and screw into the other two lemons like this. Then, using a wire and clip, connect the screw on the first lemon to the coin on the second lemon, and so on, so that the three lemon batteries are connected together. Also, connect the wire with clip to the first coin and the last screw
Finally, mark the clip connected to the first coin with "+" and the clip connected to the last screw with "+". Like a real battery pack, lemon battery pack also has positive (+) and negative (-)
When connected in series like this, these lemon batteries together produce the same voltage, or potential, as several small flashlight batteries do in series, which is about 2.5 V to 3 V. however, the lemon battery pack can not generate enough current to make the flashlight bulb shine
How can we tell if a battery pack is really realized? One way is to connect an electrical device that only needs 2.5V to 3V and does not need too much current to the battery pack. You can use a device called light-emitting diode, or LED for short. Very low voltage and small current can make the LED light up
The description on the LED box we use is: 5mm red LED, 1.8V, 20mA. This means that the diameter of the LED is 5mm, and it only needs 1.8V and 20mA to emit light, The current of less than 20 mA can make the LED light slightly. Our lemon battery has enough voltage, but the current is not enough. So we need to find some ways to observe the weak light. We put it into the film shell to isolate the external light
Using nails, carefully drill two small holes about half the height of the outer edge of the film shell. Let an adult help you do this
Next, mark one small hole with "+" and the other with "-"
Bend the pin of the led into a smooth curve outward. Then look closely at the LED. It is basically round. However, if you tilt it to a certain angle, you will see a flat surface near a pin. The pin nearest to the flat surface is the negative pole, The left pin is the negative pole of the LED. Can you see the small flat surface near the leftmost pin?
Align the negative pin of the LED with the hole on the film case marked with "-". Insert the led into the film case. Pass the negative pin of the LED through the hole marked with "-" and then pass the other (positive) pin through the hole marked with "+"
Pull the pins out of the holes and check to make sure they match the label. Also label the top of the film case. Make sure the LED is facing us
Let's get everything ready for the last moment. Align the "+" side of the LED film case with the "+" clip of the lemon battery pack. Place the "+" clip of the lemon battery pack close to the "+" side of the film case
Now everything is ready! Connect the positive pole of the led to the positive pole of the lemon battery pack. Connect the negative pole of the led to the negative pole of the lemon battery pack. The LED lights up!
The black film shell can help you to observe the dim light. The end of the LED acts as a magnifying glass. When you directly observe the end of the LED, you can easily see the luminous phenomenon
This proves that you have successfully made a usable lemon battery! Congratulations!
There's something interesting about space life
One is morning, another is night
People's long-term living habit is "work at sunrise and rest at sunset". Sleep is usually arranged at night. The circadian cycle of spaceship in space flight is different from that on earth. A day on earth is a sunset and sunrise, which is set as 24 hours. A sunset and sunrise in space flight has different periods, Because it is related to the orbit of the spacecraft around the earth. If the orbit is high, the circadian period will be long; if the orbit is low, the circadian period will be short. The circadian period of the spacecraft during the space flight, the length of day and night is inconsistent. The duration of day is long, while that of night is short. 90 minutes is a circadian period, and the longest night is only 37 minutes, It's like going from day to dusk and night. The space shuttle is very fast. When the sun comes out, it's like a "Thunderbolt", and when the sun sets, it's like a "whirlwind"
An astronaut once described a day in the universe like this: in the morning, the computer-controlled clock wakes us up. When we wake up and open the curtains to see the space, the sun is shining and the sky is beautiful. But not long after, the sun is gone, the day is dark, and the night is coming. We think it's time to go to bed again. It's very interesting, one is morning, the other is night
Density unit: 1kg / m3 = 10 negative cubic / cubic centimeter, why do you think the latter is greater than the former
1kg=1000g
1m³=1000 000cm³
1kg/m³=1000g/1000 000cm³=1/1000g/cm³
Decomposition factor 4A ^ 2 + 12ab + 9b ^ 2
4a^2+12ab+9b^2
=2*2a^2+12ab+3*3b^2
=(2a+3b)^2
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