Experiments included in the physics curriculum of middle school
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Physical experiments are related experiments included in physics courses in junior and senior high schools, including electrical experiments, mechanical experiments, thermal experiments, optical experiments, etc., which are often used to verify the laws and theorems of physics.
114. Researchuniforn variable rectinear motion The figure on the right isticker-tape timer The paper tape that has been knocked down.Select a clear plot, round off the dense plots at the beginning, take a starting point O from the place convenient for measurement, and then take a counting point A, B, C, D... (every five interval points). Measure the distance s1, s2, s3... between adjacent counting points, and use the tape to:
⑴ Calculate the instant speed v corresponding to any counting point: such as
⑶ Use any two adjacent sections in the above figuredisplacementCalculate a: as shown in the figure.
⑷ Use the v-t image to calculate a: calculate the instantaneous velocities of points A, B, C, D, E, F, and draw the v-t diagram line as shown on the right. The slope of the diagram line is the acceleration a.
Precautions 1. Every 5time intervalTake a counting point to facilitate calculation when calculating acceleration.
Use the device shown in the right figure to change the number of hook yards, measure the total length of the spring and the multiple groups of corresponding values of the tension (total weight of hook yards), and fill them in the table.Calculate the elongation of the corresponding spring.stayCoordinate systemMiddle tracing point: according to the distribution of points, make a picture that the elasticity F changes with the elongation x, so as to determine the functional relationship between F-x.Explain thePhysical meaningAnd its units.
In this experiment, the total length of the spring and the elongation of the spring should be distinguished.For exploratory experiments, try to determine the functional relationship according to the trend of the points traced.(This andConfirmatory experimentDifferent.)
Experiments to verify the parallelogram rule
116. Proof forceParallelogram ruleObjective: To experimentally study the relationship between resultant force and component force, so as to verify theParallelogram rule。
The experiment is to produce the same effect with two forces at an angle with each other and another forceParallelogram ruleWhether the resultant force and this force areExperimental errorEqual within the allowable range, ifExperimental errorIf it is equal within the allowable range, it is verifiedForce synthesisParallelogram rule of.
matters needing attention:
1. UsedSpring scaleWhether it is in good condition (whether it is at zero scale). When pulling, try not to contact with other parts to generate friction. The direction of pulling force should be consistent withaxisSame direction.
2. During the experiment, it should be ensured thatlevelwithin
Since v1, v1/and v2/are in the horizontal direction and their vertical falling heights are equal, their flight times are equalTime unit, then the horizontal range of the balls is equal to their horizontal velocity.In the right figure, it is represented by OP, OM and O/N.Therefore, it is only necessary to verify: m1 OP=m1 OM+m2 (O/N-2r).
matters needing attention:
(1) The ball with large mass must be used as the incident ball (to ensure that both balls move forward after collision).You know why?
(2) The incident ball shall slide down from the same position on the chute every time from static
(3) The average position of the ball landing point shall becompassesTo determine: circle all the falling points as small as possible, and the center of the circle is the average position of the falling points.
(5) If the impacted ball is placed at the end of the chute instead of the prop, the two balls will not land at the same time, but both balls will be made from the end of the chuteHorizontal throwing motionThen the verification formula becomes: m1 OP=m1 OM+m2 ON, and the diameter of the two small balls does not need to be measured.
Discuss how to improve this experiment:
Complex experiment
118. Study the motion of flat projectile (by tracing method)
Purpose: further clarify that horizontal throwing is a composite movement of horizontal and vertical movements, and can calculate the initial velocity of the object with the trajectory
Use cards with holes to make sureHorizontal throwing motionWhen the ball is moving, and then draw the motion track,
Measure the coordinates x and y of any point on the curve, and use
The horizontal component velocity of the ball, that is, the initial velocity of the flat projectile, can be obtained.
This experimentKey points: How to get the trajectory of an object (discussion)
Precautions for this test include:
⑴ The tangent line at the end of the chute must be horizontal. ⑵useHeavy hammerLine inspectionCoordinate paperWhether the vertical line on is vertical.
⑶ Take the point at the end of the chute as the coordinate origin.(4) Each time, the ball should slide down from the same position on the chute from standstill
(5) If white paper is used, the point at the end of the chute shall be taken as the coordinate origin and hung at the end of the chuteHeavy hammerLine, first determine the y-axis direction according to the weight line direction, and then use a right angleTriangular plateDraw a horizontal line as the x-axis to establishRectangular coordinate system。
(1) More experiments shall be carried out, and paper tapes with clear dots and a distance of 2mm between the first and second points shall be selected for measurement.
Calculate the instant speed v2, v3, v4 corresponding to points 2, 3, and 4, and verify the real-time speed v2, v3, and v4 corresponding to points 2, 3, and 4Gravitational potential energyWhether the reduction mgh is equal to the increase of kinetic energy.
Measurement of pendulum length: letSimple pendulumFree droop, withMeter gaugeMeasure the cycloid length L/(read 0.1mm) withVernier caliperMeasure the diameter of the swing ball (read 01mm), then the pendulum length L=L/+r
Attention shall be paid when starting to swing: the swing angle shall be less than 5 ° (ensure thatSimple harmonic motion）；
The suspension point shall be fixed when swinging, and the swinging shall not beConical pendulum。
Must pass the lowest point from the swing ball（Balance position）Start timing at (countdown method),
Measure the time it takes for the pendulum to make 30 to 50 full vibrations, and calculate the average value T of the period.
Change the pendulum length and repeat several experiments,
If there is no scale long enough to measure the pendulum length, can the acceleration be obtained by changing the pendulum length
121. Estimation of molecular size by oil film method
① Each drop shall be calculated in advance before the experimentoleic acidPure in solutionoleic acidActual volume ofoleic acidConcentration of solution, and thenMeasuring cylinderandDropperMeasure the volume of each drop of solution, and then calculate the volume V of pure oleic acid in each drop of solution.
② Measurement of oil film area: after the oil film shape is stableGlass platePut it on a platter and draw the shape of the oil film on theGlass plateUpper;takeGlass platePut onCoordinate paperThe unit is a square with a side length of 1cmroundingThe method of counting oil film surface
122 Draw equipotential lines on the plane in the electric field by tracing method
Used in the experimentammeterIt's zero scale in the centerammeterBefore the experiment, the relationship between the current direction and the pointer deflection direction should be measured:
takeammeterThe battery, resistance and lead wire are connected according to Figure 1 or Figure 2, where R is the resistance with high resistance and r is the resistance with low resistance. Test the other end of the ammeter with the end a of the lead wire to determine the relationship between the current direction and the pointer deflection direction.
The experiment was conducted withConstant currentCurrent field simulation ofelectrostatic field。The A electrode connected to the positive pole of the battery is equivalent to the positive polePoint charge, B connected to the negative pole of the battery is equivalent to negativePoint charge。The white paper should be placed at the bottom and the conductive paper should be placed at the top (the side coated with conductive material must be upward),Carbon paperIt is placed in the middle.
Power supply 6v: the two poles are 10cm apart and divided into 6 equal partsDatum point, and find outDatum pointpotentialEqual points.(When the ammeter does not deflectpotentialEqual)
matters needing attention:
1. The contact between the electrode and the conductive paper shall be good, and the electrode position shall not change during the experiment.
2. The conductive material in the conductive paper shall be uniform and shall not be folded.
TestedResistance wireThe resistance (usually several Ohms) of is small, so the ammeter is selected
External connection method;Power supply voltage, ammetervoltmeterrangeNeither should be too large.
This experiment does not require a voltage regulation range, which can be selectedCurrent limiting circuit。
Therefore, the circuit shown on the left below is selected.At the beginningSliding rheostatSliding ofcontactIt should be at the right end.
The current through this experiment should not be too large and the power on time should not be too long to avoidResistance wireAfter feverresistivitySignificant changes have taken place.
① BecauseSmall electric bead(i.e. small bulb) has low resistance (about 10 Ω), so it should be selectedampereTable external connection method.
② The resistance of small bulb will increase with the increase of voltage and filament temperature, and the temperature will change obviously with the voltage at low voltage. Therefore, in the low voltage area, more groups of voltage and current should be taken, so the U-I curve obtained is not a straight line.
In order to reflect this change process,
③ The voltage at both ends of the bulb should gradually increase from zero toRated voltage(The voltage varies widely).thereforeSliding rheostatThe voltage regulating connection method must be used.
In the above physical picture, the picture on the right should be selected,
④ Slide at startcontactShould be at minimumpartial pressureend(Make the voltage at both ends of the small bulb zero).
The I-U curve made from the experimental data is shown in the figure,
⑤ It means that the resistance of the filament increases with the temperature, which means that the metalresistivityIt increases with temperature.
(If U-I curve is used, the bending direction of the curve is opposite.)
Electrical experiment to verify the volt ampere characteristic curve
⑥ If the small bulb marked with "3.8V 0.3A" is selected, the ammeter shall be 0-0.6Arange；The voltmeter should be 0-3V at the beginningrangeWhen the voltage is adjusted to near 3V, the range of 0-15V shall be used.
(Ig is the full bias current, I is the scale value of the dial current, U is the maximum range of the modified meter, and is the corresponding scale of the modified meter)
(One ammeter, one voltmeter and one slideVaristor)
① Single group data calculation, with large error
② Multiple groups of (u, I) values should be measured and the average value calculated finally
③ The drawing method is used to process data, list (u, I) values, trace points in the u -- I diagram, and finally calculate more accurate E and r from the u -- I diagram line.
The reading of the voltmeter in this experimental circuit is accurate, and the reading of the ammeter is smaller than the actual current passing through the power supply,
So in this experimentsystematic errorIt is caused by shunt of voltmeter.To reduce thissystematic errorThe value of resistance R should be smaller, and the internal resistance of the selected voltmeter should be larger.
To reduceAccidental error, we should do more experiments, take more groups of data, and then use U-I image to process the experimental data:
After tracing the points, userulerDraw a straight line so that as many points as possible are on the line, and the points on both sides of the line are roughly equal.The error of U-I relation represented by this line is very small.
It is on the U axisinterceptnamelyemfE (corresponding I=0), the absolute value of its slope is the internal resistance r.
(Special attention: sometimes the starting point of ordinate is not 0, and the internal resistance is calculatedGeneral formulaShould be.
In order to make the batteryTerminal voltageThe change is obvious, and the internal resistance of the battery should be larger (select the No. 1 battery that has been used for a period of time)
① , usingDC voltagePosition (and select the appropriate range): contact the two pens with two points of A, B and C respectively, read the measurement results from the second scale line on the dial, measure the voltage between each two points, and design a table for recording.
② Use the ohm scale (and select the appropriate range) to contact the red and black probes with two points of A, B and C respectivelyRulerRead the measurement results with the scale line of, measure the positive and negative resistance between any two points, and design a table for recording.
For example: Automatica burglar alarm, TV remote control receiver, infrared detector, etc. are inseparable from sensors
The sensor will feelphysical quantity(force, heat, sound and light) into quantities that are easy to measure (generallyelectrical scienceQuantity).
Working process: through thephysical quantitySensitive element, which will feelphysical quantityIt can be converted into a signal that is convenient for use according to a certain rule, and the converted signal can be processed by the corresponding instrumentAuto-ControlAnd other purposes.
ThermistorThe resistance decreases rapidly when the temperature rises
PhotoresistorThe resistance value decreases during illumination, resulting in changes in current, voltage, etc. in the circuitAuto-Control
3. The two straight lines drawn on the paper shall be as accurate as possible and coincide with the two parallel refracting surfaces, so as to better determine the position of the entrance and exit points.
When holding the glass brick, do not touch the smooth optical surface, only the rough surface or edge,
It is forbidden to use glass brick as a ruler to draw the interface of glass brick;During the experiment, the relative position of glass brick and white paper cannot be changed;
PinIt shall be inserted vertically on white paper, and twoPinThe distance should be larger to reduce the error caused by determining the direction of the light path;
Angle of incidenceIt should be larger to reduce the error of measuring angle.
Equipment: light holder, light source, student power supply, wirefilter, single seam, double seam, shading cylinderGround glassScreen
Measuring head, scale
The distance between two adjacent bright (dark) stripes;Measure a1 and a2 with measuring head (using accumulation method)
Measure the distance a between n bright (dark) stripes, and calculate
Double slit interference: condition f is the same,phase differenceWhat if it is constant (that is, the vibration steps of two lights are exactly the same) when it is in opposition?
Position of bright stripe: Δ S=n λ;
Dark stripe position: (n=0,1,2,3,,,);
Stripe spacing:
(Δ S: distance difference（Optical path difference)；D Distance between two slits;50: Distance between baffle and screen) Measure the distance a between n bright stripes
VoltammetryThere are two connection methods for measuring resistance: a and b（ampereExternal connection method, b is called（ampereInternal connection method.
① Estimate the resistance value of the measured resistance to judge the internal and external connection method:
The system error of the external connection method is caused by the shunt of the voltmeter, and the measured value is always less than the true value. The external connection method should be used for small resistance;The system error of the internal connection method is caused by the voltage division of the ammeter. The measured value is always greater than the true value. The internal connection method should be used for large resistance.
② If the value of the measured resistance cannot be estimated, you can useTouch test method：
As shown in the figure, connect the left end of the voltmeter to point a, connect the right end to point b for the first time, and connect the right end to point c for the second time, and observe the changes of the ammeter and voltmeter,
If the reading of the ammeter changes greatly, it means that the measured resistance is large, and the internal connection method should be used for measurement;
If the reading of the voltmeter changes greatly, it means that the measured resistance is small, and the external connection method should be used for measurement.
(The big change here refers to the relative change, namely Δ I/I and U/U).
slideVaristorIn the circuit, there are also two common connection methods, a and b: a is called current limiting connection, and b is called sub crimping connection.Partial voltage connection: the voltage on the measured resistance can be adjusted in a wide range.
When voltage is requiredStart from zeroWhen adjusting, or the voltage adjustment range is required to be as large as possible, the sub crimping method should be used.
When using the partial crimping method, the sliding rheostat should choose the one with small resistance value;"Control the big with the small"
When using the current limiting connection method, the sliding rheostat should have a value close to the measured resistance.
(2) Connection technology of physical picture
Either the partial crimping connection or the current limiting connection should be connected firstVoltammetryPartial connection;
Just use the stroke line as the wire, start from the positive pole of the power supplyKey, sliding rheostatvolt-ampereThe four parts of the method can be connected in series (notewatt-hour meterThe positive and negative terminals and range of the sliding rheostat should be adjusted to the maximum resistance).
For voltage divider circuit,
The power supplyKeyAnd sliding rheostatResistance wireThe three parts are connected by wires, and then select a connector at either end of the resistance wire of the sliding rheostat, and compare the connector with the sliding rheostatcontactThe potential of two points is high or low,
according tovolt-ampereFor the positive and negative terminals of some meters in Francevolt-ampereThe French part is connected between the two points.
High speed target pair of electrons accelerated by high pressurecathode, fromcathodeUpstroke emissionX-ray。Between K and ACathode rayI.e. high speedElectron flow, what is emitted from A is an extremely high frequency electromagnetic wave, that isX-ray。X-rayThe highest possible frequency of the particle can be calculated by Ue=h ν.
All devices are placed in vacuum.The screen can rotate along the dotted line in the figure to count the number of particles scattered in different directions.The observation is that mostAlpha particlego throughGold foilAfter that, they basically moved in the same direction, but there were a fewAlpha particleA large deflection occurred.
Connect a polished zinc plate to LingmeiElectroscopeUp, usingArc lampZinc plate,ElectroscopeThe pointer of is opened at an angle, indicating that the zinc plate is electrified. Further inspection shows that the zinc plate is electrified. This indicates thatArc lampUnder the irradiation of, part () of the zinc plate flew out from the surface, and there was less () in the zinc plate, so () was electrified
Junior High School Physics Experiment
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buoyancy
When "exploring what factors are related to the size of buoyancy", students proposed the followingguess：
In order to verify the above conjecture, Li Ming made an experiment as shown in Figure 28: he hung an iron block under the spring dynamometer and slowly immersed it in different positions in the water in turn. In this experiment:
(1) During the process of iron block moving from position 1 to 2 to 3, the indication of spring dynamometer indicates the buoyancy of iron block;In the process of position 3-4, the indication of the spring dynamometer indicates the buoyancy on the iron block.(Fill in "larger", "smaller" or "unchanged")
(2) This experiment can verify that the above conjecture is correct and the conjecture is incorrect (fill in the number of conjecture above).
(3) Here is a glass of water, a cooked egg and an appropriate amount of salt (as shown in Figure 29). Please design an experiment to verify whether the buoyancy is related to the density of the liquid.Briefly write your experimental verification method
Inclined plane
Figure 30 is Xiaoliang measurementInclined planeMechanical efficiencyOfdevicechart。During each experiment, the trolley being pulled moves upward at a uniform speed along the same slope.The following table is a table designed by Xiao Liang to record data.(1) When it is "steep", the effective work is _____;The total work is ____;The mechanical efficiency is _____;
(2) What conclusions can you draw by analyzing the experimental data in the table?(Two items are required)
Inclined plane
a．_________________；b．_________________．33、A student designed an experiment scheme as shown in Figure 31 in the experiment of exploring "what factors are related to the size of kinetic energy", and carried out the following experiments:
Step l: Let the steel ball slide down from a standstill at point A of the inclined plane. When it reaches the horizontal plane, the speed is v1. Hit the wooden block and make it move. Record the distance S1 of the wooden block;
Step 2: Let the steel ball slide down from a standstill at point B of the inclined plane. When it reaches the horizontal plane, the speed is v2.: Hit the wooden block and make it move. Record the distance S2: that the wooden block moves
Step 3: change the mass of the steel ball so that the steel ball slides from the stationary point A, hit the wood block and move it, and record the distance S3 of the wood block.
(1) Comparing v1 and v2, we can see that vl ______ V2 (">", "<", "=" are optional) is because _______________.
(2) Steps l and 2 are designed to ________________.
(3) Comparing step and step 3 can explore the relationship between kinetic energy and object ______.
Gravitational potential energy
Gravity potential energy experiment
In "ExploreGravitational potential energyWith whichfactorIn the experiment of "related", Xiao Hua conjectured that: A. the size of the gravitational potential energy of an object may be related to the height of the object being lifted B. The size of the gravitational potential energy of an object may be related to the size of the object'squalityofHe chose water-based pen, rubber, paper and transparent glue as experimental equipment to use the destructive power of objects when fallingverificationHisguess。
(1) The same physical problem that these two experiments can explain is:
(2) OnSimple pendulumIn the process of swinging from left to right and rolling up and down, you will see that their rising height gradually decreases.
To compare water and sandheatXiaoming filled water and sand in two identical beakers.Heat it with two identical alcohol lamps.
(1) Before the experiment, the __________ and __________ of water and sand should be controlled to be the same.
(2) The method to compare the heating speed of water and sand: the heating time is the same and compare their respective rising temperatures.
Work and power
someschoolBought a new casePhysicsequipmentXiaoyun moved it from the first floor to the third floor, and Xiaobin wanted to measure the power of Xiaoyun to do work on the box in the process of moving equipment
[Experiment steps]
(1) The measurement steps designed by Xiao Bin are as follows, among which the redundant ones are:
A. Measure the mass of the box m B. Measure the total length of the stairs L
C. Measure the vertical height from the first floor to the third floor h D. Measure the time t taken for Xiao Yun to go upstairs
E. Calculate the power P of Xiao Yun's box handling
⑵ Please help Xiaobin design a table to record the experimental data in the dotted box.
A current IA B current IB C current IC
First measurement 0.10 0.12 0.22
Second measurement 0.20 0.24 0.44
The third measurement 0.25 0.30 0.55
Measuring electric power
There is one in Xiaoming's familyElectric blanketThe nameplate is marked with "220V, * * W", of which the rated power value is unclear, between 40W and 60W.The laboratory has the following experimental equipment:
One battery (voltage is 6V), one switch and several wires.In addition, the following equipment are available:
