A piece of wire is wound on the pencil for 20 turns, and the width of 20 turns is 20 mm measured with a scale. The diameter of the wire is? Mm I'm in a hurry

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• 1. A wire with a length of 50cm is tightly wound on the pencil rod for 30 turns, and the width of 30 turns is measured with a scale, then the diameter of the wire is () mm (2) μ M
• 2. How to measure the diameter of 100cm wire
• 3. As shown in Figure 1, two long enough straight metal guides Mn and PQ are placed in parallel. The distance between the two guides is l0, m and P, and there is a resistance of R indirectly. A uniform straight metal rod AB with mass of M is placed on the two guides and perpendicular to the guide rail. The whole device is in a uniform magnetic field with magnetic induction intensity of B, and the magnetic field direction is perpendicular to the inclined plane downward. The resistance of the guide rail and the metal rod can be ignored Let the AB rod slide down along the guide rail from rest, and the guide rail and the metal rod have good contact, regardless of the friction between them. (1) the device seen from B to a direction is shown in Figure 2, in which the force diagram of AB rod at a certain time in the process of sliding is drawn; (2) when the speed of AB rod is V, the current and acceleration of AB rod at this time are calculated; (3) when the speed of AB rod is V, the force diagram of AB rod is obtained In the process of sliding, the maximum velocity can be reached by ab bar
• 4. 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
• 5. As shown in figure a, the smooth parallel guide rails Mn and PQ are placed horizontally without resistance. The distance between the two guide rails is d = 10cm. The conductor rods AB and CD are placed on the guide rails and perpendicular to the guide rails. The resistance of each rod between the guide rails is r = 1.0 Ω. The two rods are tied with insulated wire with length of L = 20cm. When the whole device is in a uniform magnetic field. T = 0, the magnetic field direction is vertical and downward, and the wire is just in the ungrounded position After that, the change of magnetic induction intensity B with time t is shown in Fig. B. the influence of the induced current magnetic field is not taken into account. The whole process of the wire is not broken
• 6. As shown in the figure, the uniform electric field in a certain space is vertically downward, the uniform magnetic field is vertically inward, and a metal bar AB falls freely from high h, then () A. A end first landing B. B end first landing C. both ends simultaneously landing D. the above statements are not correct
• 7. As shown in the figure, PQ is a thin metal sheet in a uniform magnetic field, and its plane is parallel to the direction of the magnetic field. A charged particle shoots out from a certain point at a velocity V perpendicular to PQ, and the kinetic energy is e. the trajectory of the charged particle after shooting is shown in the figure. The ratio of its trajectory radius on both sides of the metal sheet is 10:9. If the resistance and electric quantity of the particle are constant in the process of passing through the plate, it can be seen as follows, Then () A. Charged particles must be positively charged. B. the velocity of charged particles decreases by 1102emc every time they pass through the metal sheet. The kinetic energy of charged particles decreases by 0.19ed every time they pass through the metal sheet. The charged particles are trapped in the metal sheet after they pass through five times
• 8. A rectangular granite is 10 meters high, 3 meters wide and 2 meters thick, with a density of 2.5 x 10 cubic kilogram per cubic meter. The maximum bearing capacity on the ground is
• 9. How many tons of tire oil can a 3 m long and 1.2 m wide rectangle hold? The density is 0.5
• 10. A granite stone with school motto has a mass of 3.18 × 104 & nbsp; kg and a density of 2.65 × 103 & nbsp; The density of brick is known to be 2.05 × 103kg / m3, and the density of cement mortar in the base brick joint is the same as that of brick (G is 10N / kg) (1) The volume of granite stone; (2) the pressure of stone on base; (3) the ratio of stone to base and base to ground
• 11. In order to measure the diameter of the thin copper wire, a student arranged the thin copper wire tightly on the pencil for 30 turns, as shown in the figure. From the figure, we can see that the length of the coil is______ Cm, the diameter of copper wire is______ cm．
• 12. The weather is very hot. Use a balance and a scale to measure the density of a cube of uniform mass. The scale is made of a metal material which is sensitive to temperature The side length of the cube measured by the scale will be smaller than that measured by the standard room temperature
• 13. There is a mess of wire which can't be straightened out. Please use your measuring tools to measure its length quickly It is required to write out the main steps and calculation formula of the measurement method 1. Give you a scale with the minimum scale value of mm and a pallet balance Here is a round pencil, a ruler and a large cup
• 14. Measurement 1. The thickness of a piece of paper 2. The height of a building 3. The diameter of a ping-pong ball 4. The diameter of a thin wire 5. The length of a bending workpiece
• 15. The length of the wire can be obtained by knowing the cross section, density and mass of the wire That is why it is best to deduce other formulas, such as known wire length, cross section mass, metal density, etc
• 16. To measure the diameter of a thin wire, there is an 80cm wire, a pencil and a millimeter scale. Design the measurement scheme and write the results
• 17. It is known that the standard value of 1 standard atmospheric pressure is about 10 to the fifth power Pascal. Xiao Ming wants to explore the atmospheric pressure through experiments. His experimental scheme is to press the plastic hook suction cup dipped in water on a smooth horizontal table, squeeze out the air inside, and measure the reading with a spring dynamometer. This is the pressure of the atmosphere on the suction cup: then try to measure the contact area between the suction cup and the table, Then calculate the atmospheric pressure Q: Xiao Ming has chosen a spring dynamometer with a measuring range of 100 n. please explain by calculation the size of the suction cup with the bottom area at least so as to carry out the experiment smoothly? (assuming that the air in the suction cup is completely squeezed out)
• 18. A student measured the length of an object with a ruler with the minimum scale value of 1 mm, and made the following records: ① 18.74 cm, ② 1.87 × 10 quartic mm A student measured the length of an object with a ruler with the minimum scale value of 1 mm, and made the following records: ① 18.74 cm, ② 1.87 × 10 quartic mm, ③ 0.187 m, ④ 1.874 × 10 quadratic mm A. ① and ③ B. (1) and (4) C. (2) and (4) D. All meet the requirements
• 19. If a = 8, then the greatest common factor of a and B is the least common multiple Is (?) [3] the common factors of 18 and 34 are (?), the greatest common factor is (?), and the least common multiple is (?)
• 20. There are four natural numbers less than 10, and their product is 360. It is known that there is only one composite of the four numbers. What are the four numbers?