As shown in the figure, in a uniform magnetic field, the resistance of two parallel metal guide rails Mn and PQ is ignored, AB and CD are two metal slide rods As shown in the figure, in a uniform magnetic field, the resistance of two parallel metal guide rails Mn and PQ is not included, AB and CD are two metal slide rods, and the resistance rabf2 and UAB

Because the magnetic field force F = bil, AB, CD and guide rail form a closed circuit, in which the current intensity is equal, the pole length phase and so on are in the same magnetic field, B is the same, so F1 = F2; UAB is the closed circuit and the terminal voltage (AB is equivalent to the power supply), UCD is added to the CD pole (equivalent to the resistance of the external circuit), so the external circuit has only one resistance, and the so-called terminal voltage is the voltage added to both ends of the resistance, So UAB = UCD, so B

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1. As shown in the figure, the distance between two sufficiently long parallel smooth metal guide rails Mn and PQ is, the angle between the guide rail plane and the horizontal plane = 30 °, the resistance of the guide rail is not included, and the magnetic resistance is not included The uniform magnetic field with the strength of B is perpendicular to the plane of the guide rail and upward. The metal plate AB with the length of D is perpendicular to Mn PQ and placed on the guide rail, and always has good contact with the guide rail. The mass of the metal bar is m, and the resistance r = R. a bulb is connected to the upper end of the guide rail of the two metal bars, and the resistance RL = R of the bulb and the acceleration of gravity is g, A constant force of F = mg is applied to the metal rod in the direction perpendicular to the rod and parallel to the plane of the guide rail to make the metal rod move from static state. When the metal rod reaches the maximum speed, the bulb can just reach its rated power (1) The maximum velocity VM that metal bar can reach (2) Rated power of bulb pl (3) Acceleration a when the metal bar reaches half of the maximum speed (4) If the maximum sliding distance of the metal bar is l, calculate the electric heat QR generated on the metal bar during the process of the metal bar sliding up 4L from static state
2. As shown in the figure, the smooth U-shaped metal frame is still on a horizontal plane in a vertical downward uniform magnetic field. Now the AB rod suddenly obtains an initial velocity V and moves to the right A. B. the current in the circuit decreases uniformly. C. the potential of point a is lower than that of point B. D. the U-shaped frame moves to the right
3. As shown in the figure, the metal bar PQ moves to the left () A. When the rod is moving at a constant speed, the potential difference between a and B is not equal to zero. B. when the rod is accelerating, the current direction in coil N changes from a through n to B. C. when the rod is accelerating at a constant speed, there may be C → D current in bulb D. when the rod is decelerating, there may not be C → D current in bulb L
4. There is a monument. The total mass of the upper stone is 100t, and the height of the lower cornerstone is 1m. If the density of the cornerstone is 2 * 10 cubic kg / m3, and if the ground can bear the pressure of 68600, what is the bottom area of the cornerstone at least Another question: a piece of wood has a density of 400kg / m3 and a volume of 0.000056 m3. Put a frog on the block and the block floats on the water. The upper surface of the block is just level with the water surface. How much does the frog weigh?
5. There is a monument with a mass of 10t standing on the foundation stone of a cuboid, as shown in the figure. The density of the foundation stone is 2 × 103kg / m3, and the design height is 1m. If the maximum pressure on the ground at the place where the monument is erected is 1.4 × 105Pa, what is the bottom area of the foundation stone? (take g = 1On / kg)
6. This granite is 14.7 meters long, 2.4 meters wide and 1 meter thick. What's its mass? The density of granite is 2.8 * 10 cubic kg / M cubic
7. The height, width and thickness of a rectangular flower jar monument are 10m, 3M and 2m respectively, and the density is 2500kg / M & sup3; the ground can bear the maximum pressure of 150000pa. In order to make the ground can bear the monument, the monument is erected on the rectangular cornerstone with the height of 1m and the density of 2000kg / M & sup3 (1) What is the quality of the monument? (2) If the monument stands directly on the ground, what is its pressure on the ground? (3) what is the minimum bottom area of the cornerstone?
8. The height, width and thickness of a rectangular flower rock monument are 10m, 3M and 2m respectively, the Rou is 2.5 × 103 times, and the maximum pressure on the ground is 1.2 × 103 times. In order to make the ground bear the monument, the height of the monument is 1m, the Rou is 2 × 103 times, so that it can be put on the rectangular cornerstone? 2 if the monument stands directly on the ground, the pressure on the ground is?
9. The mass of a granite stone with school motto is 31.8t and the density is 2.65 × 103kg / m3. It is erected on a horizontal base with a length of 4m, a width of 2M and a height of 0.5m (as shown in the figure). The contact area between the stone and the base is 2.12m2. The density of the known brick is 2.05 × 103kg / m3. The density of the cement mortar in the base brick joint is the same as that of the brick. (G is 10N / kg) Volume; (2) the pressure of stone to base; (3) the ratio of stone to base and base to ground
10. Giraffe is the tallest animal with an average height of 4.3 meters and a blood density of about 1.05 × 103kg / m3. When the giraffe's heart contracts and presses the blood into the brain which is 3 meters higher than the heart, the pressure is at least 10%______ Pa．
11. As shown in the figure, Mn and PQ are two metal rails horizontally placed in parallel with each other, and the magnetic induction line with uniform magnetic field is vertical As shown in the figure, Mn and PQ are two metal rails horizontally placed parallel to each other. The magnetic induction line of uniform magnetic field is perpendicular to the plane of the guide rail. The left end of the guide rail is connected with a resistance of resistance value. A voltmeter is connected at both ends of the resistance. The vertical guide rail is connected across a metal rod ab. the mass, resistance and dynamic friction coefficient between AB and the guide rail are μ = 0.5, and the resistance of the guide rail is ignored. Now the constant force of F = 0.7n is used to pull AB horizontally to the right, Let it start to move from rest. After time, AB starts to move at a constant speed. At this time, the voltage expression u = 0.3V, the acceleration of gravity. Find (1) the power of external force F when AB moves at a constant speed. (2) the electric quantity passing through R during the acceleration of AB rod Mainly ask the second question, I searched, there is a "impulse theorem" to do the second question, but we did not learn. Is there any other way to ask the second question?
12. As shown in the figure, Mn and PQ are two parallel metal guides placed in the vertical plane and long enough, with a distance of L = 50cm. The guide is in the uniform magnetic field with a vertical paper inward magnetic induction intensity of B = 5T. A metal bar AB with a resistance of 0.1 Ω can move left and right close to the guide. Two parallel metal plates a and C with a phase distance of D = 10cm and a length of L = 20cm are connected with the two parallel guides respectively It is known that when the metal bar AB is not moving, the small ball with mass m = 10g and charge q = - 10-3c shoots into the plate along the middle line of metal plate A and C at a certain speed V0, and can just shoot out the metal plate (G is taken as 10m / S2) (1) The velocity of the ball V0; (2) if the ball does not deflect between the metal plates, the velocity and direction of the metal bar AB; (3) if the ball can be ejected between the metal plates, what conditions should be met for the uniform velocity of the metal bar AB?
13. As shown in the figure, Mn and PQ are parallel smooth metal guide rails with a spacing of L. they are placed in a uniform magnetic field with a magnetic induction intensity of B and a direction perpendicular to the plane of the guide rail. M and P indirectly have a resistance of R. a metal wire AB with good contact with the guide rail and an effective resistance of R2 is placed vertically on the guide rail and moves to the right at a uniform speed V under the action of horizontal external force F, regardless of the resistance of the guide rail , then () A. The direction of current through resistance R is p → R → MB. The voltage between two points is blvc. The potential at a end is higher than that at B end. The work done by external force F is equal to Joule heat generated in the circuit
14. How to measure the diameter of wire There is a long, thin wire, which looks like hair. How to measure the diameter of the wire roughly with a scale? Write down what you do
15. When re measuring the diameter of the wire, the wire is tightly and evenly wound on the pen, the number of turns is 16, and the length of the wire is 16 It's 25 mm. What's the diameter of the thin wire?
16. How many mm is the length of the filament and how many mm is the diameter of the filament? It's like winding in a circle
17. Use a piece of wire on the pencil and wind it for 20 turns. As shown in the figure, use a scale to measure the width of 20 turns______ Mm. The diameter of this wire is______ Mm
18. Cycle,
19. How many centimeters is the circumference of a rectangle made by flattening five squares with 10 cm sides into a rectangle?
20. Is the distance of a harmonic motion passing through a half periodic particle twice the amplitude?