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18. There are orthogonal uniform electric fields and uniform magnetic fields under the horizontal dotted line MN near the ground. The electric field intensity is E and the magnetic induction intensity is B, as shown in the figure. A charged particle falls from a height with a distance MN of h, enters the field from point P, moves along the semi-circular arc POQ, and leaves from point Q through the lowest point O of the circular arc. The acceleration of gravity is g, ignoring the influence of air resistance. The following statements are wrong: a. The direction of electric field force received by particles after entering the stadium must be vertical upward; B. When the particle enters the field, it moves in a circle with a radius of.
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C. During the movement from point P to point Q, the electric potential energy of particles first increases and then decreases. D. In the process of moving from point P to point O, the sum of electric potential energy and gravitational potential energy of particles becomes smaller and smaller.
19. As shown in the figure, the electromotive force of the power supply is E, the internal resistance is R, and the fixed resistance is R..
The resistance of is also r, and the maximum resistance of sliding rheostat is 2r. When the slider P of the sliding rheostat slides from the end A to the end B, the following statement is correct.
A. The indication of voltmeter becomes larger B. The indication of ammeter becomes smaller C. The power consumed by sliding rheostat becomes smaller.
D. the power consumed by the constant value resistor r first becomes larger and then becomes smaller.
20. As shown in Figure A, the insulation board with a mass of 2kg is still on the rough horizontal ground, with a mass of 1kg and a side length of1m..
The square metal frame ABCD with resistance of 0. 1ω is located on the insulation board, and E and F are the midpoint of BC and AD respectively. At a certain moment, there is a vertical downward magnetic field in ABEF area, and the law of its magnetic induction intensity B 1 changing with time is shown in Figure B, and the AB edge is just outside the magnetic field edge. There is a vertical uniform magnetic field in FECD area, the magnetic induction intensity B2=0.5T, and the edge of CD is just inside the magnetic field edge. Assuming that the maximum static friction on the metal frame is equal to the sliding friction, both magnetic fields have ideal boundaries, g = 10m/S2. rule
A. the induced electromotive force generated in the metal frame is 1V B. The magnitude of ampere force on the left side of the metal frame is 1N C. The direction of induced current in the metal frame is ADCB direction.
D. If the dynamic friction coefficient between the metal frame and the insulation board is 0.3, the metal frame can remain static on the insulation board.
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2 1.( 18 points)
(1) (6 points) The experimental device of "Measuring the wavelength of light with double-slit interference" is shown in Figure A ... The measuring head consists of a reticle, an eyepiece and a handwheel. It is known that the distance between the double seam and the screen is L, and the distance between the double seams is D. ..
① As shown in Figure B, move the handwheel on the measuring head to mark the center of the reticle.
Align the center of the bright line 1 and record the reading of the spiral micrometer on the handwheel at this time. Turn the measuring head and move the center reticle to the right to align with the center of the fourth bright particle. At this time, the reading x2 of the screw micrometer on the handwheel is shown in Figure C, and the reading x2 is _ _ _ _ _ _ _ mm.
(2) known the distance between the double slit and the screen is L, and the distance between the double slits is D. The calculation formula of wavelength λ = _ _ _ _ _ _ _; (indicated by the letters given in the title)
(3) For monochromatic light, in order to increase the distance between adjacent bright lines, _ _ _ _ _ _ _ _ or.
_ _ _ _ _ _ _ _ _ method.
(2)( 12) In order to measure the dynamic friction coefficient between the wood block and the long board, the laboratory can provide the following equipment: END A.
A fixed long wooden board with adjustable height at the B end, a small wooden block, a timer and a meter ruler. Given that the acceleration of gravity is g, ① fill in appropriate formulas or words and improve the following experimental steps:
A. Adjust the height of the B end of the long board, so that the block slides down from the C point on the board to the board.
At the bottom a, use a timer to record the time t when the slider slides down.
B. Measure the distance s between C and A with a meter ruler, and the falling acceleration of the wood block is a =. C. measure the height h of the b end of the long board relative to the horizontal desktop and the total length l of the long board with a meter ruler. According to Newton's second law, the expression of dynamic friction coefficient between wood block and long board can be obtained? =____________。 (expressed by experimental measurement)
D. Change the average value of _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. ② In the above experiment, in order to reduce the experimental error, a classmate measured several accelerations a 1, a2, a3 by changing the inclination angle θ of the inclined plane, calculated the average value A of these accelerations, and used this average value to calculate the friction coefficient. Do you think this classmate's method is correct, and explain the reasons?
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22.( 16) It is known that the total mass of the child and the sled is m = 20 kg, which is still on the horizontal ice, between the sled and the ice.
What is the coefficient of dynamic friction? = 0. 1。 It is known that sin37 = 0.6, COS 37 = 0.8, and G is 10m/s2. (1) Adults use the horizontal constant push of F 1=30N to find the distance L after sled movement for 4 seconds;
(2) As shown in the figure, if an adult uses a constant force with a size of F2=50N and an angle of 37 with the horizontal direction to pull the sled obliquely upwards,
Let the sled move 1m from the static state, and then remove the tension to find out the total distance between the child and the sled on the ice.
23.( 18 points) As shown in the figure, the two roots are long enough and smooth, and the distance is d.
The parallel metal guide rail is located in the horizontal xoy plane, and the left end is connected with a resistor with a resistance value of R, and the resistance of other parts can be ignored. There is a vertical downward magnetic field on the x>0 side, and the magnetic induction intensity changes according to B=kx (where k > 0 is a constant). The metal rod with the mass of m and the metal guide rail are vertically installed on the guide rail, and the contact is good. At a certain position where x < 0, the metal rod is subjected to an instantaneous impulse, and the velocity obtained is v0, and the direction is along the positive direction of the X axis. Q:
(1) The total heat generated on the resistor R during the movement of the metal rod; (2) If the time is counted from the moment the metal bar enters the magnetic field, there is always one.
The variable force f to the left acts on the metal rod, so that the acceleration of the metal rod is always A and the direction is always in the negative direction of the X axis. It is found that: a. the duration of induced current in closed loop;
B what is the expression of the relationship between the external force f and the time t when the metal rod moves in the magnetic field?
24.(20 points) Conveyor belts are widely used in all walks of life. Because the dynamic friction coefficient between different objects and the conveyor belt is different, the motion of objects on the conveyor belt is also different. As shown in the figure, the inclined conveyor belt has an inclination angle θ = 370 with the horizontal plane, which is driven by a motor and runs clockwise at a speed of V = 2m/s. M and N are the two ends of the conveyor belt, and the distance between two points MN is L=7m. At the N end, there is a baffle P near the conveyor, which can block the objects on the conveyor belt. Metal block a and wood block b are continuously released at the o position on the conveyor belt. The mass of metal block and wood block is 1kg, which can be regarded as particles. The distance between OM is L=3m. Sin37 = 0.6, cos 37 = 0.8, and g is 10m/s2. Regardless of the friction on the shaft, there is no relative sliding between the conveyor belt and the wheel.
(1) After the metal block A is released from the static state, it moves upward along the conveyor belt and passes through it.
2s reaches the M end, and the dynamic friction coefficient μ 1 between the metal block and the conveyor belt is calculated.
(2) After being released from the static state, the wood block B moves downward along the conveyor belt and collides with the baffle P ... It is known that the collision time is very short.
The velocity of wood block B is unchanged before and after collision with baffle P, and the dynamic friction coefficient μ 2 between wood block B and conveyor belt is 0.5. Q:
A. the distance between the highest position reached by the block b and the baffle p after the first collision and the baffle p; B, after a long enough time, the output power of the motor remains unchanged, and the output power of the motor at this time is found.
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