Name symbol name symbol
Mass m kg kg m=ρv
Temperature t centigrade℃
Speed v m/sec m/sec v = sec/sec
Density ρ kg/m 3 kg/m3 ρ=m/v
Kg/m3 3 kg/m3
Force (gravity) f Newton (cattle) N G=mg
Pressure p Pascal (Pa) Pa P=F/S
Work w joule (coke) J W=Fs
Power p watt (watt) w P=W/t
Current I Ampere (A) A I = U/R.
Voltage u volts (volts) V U=IR.
Resistance r ohm (ohm) ω r = u/i.
Electric power watt Joule (joule) watt =UIt
Electric power p watt (W) w P=W/t=UI.
Heat q joule (coke) J Q = cm (t-t0)
Specific heat C Jiao/(kg Celsius) J/ (kg Celsius)
The speed of light in vacuum is 3x108m/s.
9.8 N/kg
15 C the speed of sound in the air is 340 m/s.
Safe voltage is not higher than 36 volts.
1, liquid pressure p = GH2. Archimedes principle F float = G drain = gV drain3. Lever balance
Conditions: f1l1= f2l2; 4. Mechanical efficiency = ×100%; 5. Joule's Law: Q = I2RT
(q = w)； if the circuit is a pure resistance circuit); 6. If you know the rated voltage U and rating of an electrical appliance.
Power p, and the actual voltage u is a real number, then the resistance of the electrical appliance during normal operation is r = p Real number = =( )2P.
; 7. Power p = Fv8. Characteristics of series circuit: I = I1= I2; u = u 1+U2； r = r 1+R2；
. Characteristics of parallel circuit: I = I1+I2; U 1=U2=U
force
Line m: mass of displacement liquid.
ρ liquid: density of liquid
The fifth line: the volume of liquid discharged.
(i.e. the volume immersed in liquid)
Lever balance condition f1L 1 = f2l2f1:power l1:power arm.
F2: resistance L2: resistance arm
Crown block F=G object
S=h F: tension at the free end of the rope.
G object: the gravity of the object.
S: the distance that the free end of the rope moves.
H: the rising distance of the object.
Moving pulley F= (G object +G wheel)
S=2 h G object: the gravity of the object
G wheel: the gravity of the moving pulley.
Pulley block F= (G object +G wheel)
S=n h n: the number of rope segments passing through the moving pulley.
Mechanical work w
(J) W=Fs F: force
S: distance moved in the direction of force.
effective work
Total work w total w has =G substance h
W total =Fs is suitable for the case that the pulley block is placed vertically.
Mechanical efficiency η= × 100%
Power supply p
(w) P=
Woman: Work.
T: time
Pressure p
(Pa) P=
pressure
stressed zone
Liquid pressure p
(pa) p = rhogh rho: liquid density.
H: depth (from liquid level to required point)
Vertical distance)
Heat q
(J) Q=cm△t c: specific heat capacity m: mass.
△t: change value of temperature
Fuel combustion emission
Q(J) Q=mq m: quality
Q: calorific value
1. Objects that can emit light by themselves are called light sources, such as the sun, lighted candles and electric lights. They can emit light by themselves, all of which are light sources.
2. Light propagates in a straight line in the same uniform medium.
3. The speed of light in vacuum is 3× 108m/s, which is faster than that in other transparent media.
4. Light reflection
(1) When light strikes the surface of an object, the propagation direction changes.
Backward light returns to the original medium and continues to spread, which is the phenomenon of light reflection.
(2) The content of the reflection law of light is that reflected light, incident light and normal are on the same plane; Reflected light and incident light are separated on both sides of the normal; The reflection angle is equal to the incident angle.
(3) When a parallel beam hits a smooth mirror, the reflected beam is still a parallel beam. This reflection is called specular reflection.
When the parallel light beam hits the uneven reflecting surface, the reflected light is no longer parallel, but irregularly scatters in different directions. This reflection is called diffuse reflection.
Every ray in specular reflection and diffuse reflection follows the law of light reflection.
5. Flat mirror
(1) Imaging Law of Plane Mirror: Plane mirror forms a virtual image, which is the same size as the object, and their connecting lines are perpendicular to the mirror surface, and their distances from the mirror surface are equal.
6. Spherical mirror
(1) concave mirror
Concave mirror can concentrate light, and it has real focus.
(2) A convex mirror that uses the outer surface of a sphere as a reflecting surface is called a convex mirror.
A convex mirror diverges light, and it has a virtual focus.
7. Refraction of light
(1) When light is injected from one medium into another, the propagation direction of light generally changes at the interface between the two media, which is the refraction of light.
(2) Law of refraction of light: refracted light is the same as incident light and normal line.
On the plane; Refracted light and incident light are separated on both sides of the normal; Figure 2
When light obliquely enters other transparent substances such as water or glass from the air, the refraction angle is smaller than the incident angle; When light enters the air obliquely from other transparent media such as water or glass, the refraction angle is greater than the incident angle.
8. lens
(1) The refractive surface is two spherical surfaces, or one is a spherical surface and the other is a plane transparent body, that is, a lens.
(2) A lens with a thick center and a thin edge is called a convex lens.
A convex lens condenses light, and it has two real focal points.
(3) A concave lens with a thin edge in the middle is called a concave lens.
A concave lens diverges light and has two virtual focal points.
9. The law of convex lens imaging
(1) When u > 2f, the inverted image, the reduced image and the real image can be obtained through the convex lens, and the real image is on the other side of the lens within the range of f < v < 2f. The camera is the application of the law of convex lens.
(2) when f < v < 2f, an inverted magnified real image can be formed through the convex lens, and the real image is on the other side of the lens and within the range of V > 2f. The slide projector is the application of the law of convex lens.
(3) When u < f, the convex lens can form an upright magnified virtual image, and the virtual image and the imaged object are on the same side of the convex lens. Magnifier is the application of the law of convex lens.
1. Sound generation
Everything that makes a sound is vibrating. Vibration is the cause of sound.
Example 1 When drumming, the scraps of paper scattered on the drum surface will jump, and the louder the drum sound, the higher the scraps of paper jump; When the sounding tuning fork touches the water surface, it can splash, and the louder the sound of the tuning fork, the greater the splash; The paper cone vibrates when the speaker sounds. The louder the sound, the greater the amplitude of the paper cone. According to the above phenomenon can be summarized as follows:
(l) Sound is produced by _ _ _ _ of an object;
(2)_______。 (Wuxi, 2004)
The similarity of the three phenomena is that the object that is making sound can cause the vibration of other objects, indicating that the sound is produced by the vibration of objects.
The louder the drum sound, tuning fork sound and speaker sound, the greater the vibration of scraps of paper, water spray and paper basin, indicating that the greater the vibration amplitude, the louder the sound.
2. The spread of sound
Sound travels through the media. The medium can be gas, liquid or solid. The sound we usually hear is transmitted through the air.
Meteors make a loud noise when they land on the earth, but when they land on the moon, even if astronauts are nearby, they can't hear the sound. This is because ()
(a) The surface of the moon is silent when it is hit.
(b) The impact sound is too low for human ears to hear.
There is no air on the surface of the moon, so sound can't travel.
(d) The impact on the moon generates ultrasonic waves. (Xuzhou in 2005)
Analysis of sound transmission needs medium, there is no air on the surface of the moon, and vacuum can't transmit sound, so choose (c).
Fishermen living by the sea often see such a scene: the wind is sunny and there are handfuls of small "parachute" jellyfish on the calm sea. They rise and fall in the offshore area and drift leisurely. Suddenly, the jellyfish left the coast and swam to the sea as if they had received some orders. After a while, the wind roared and the waves were rough, and the storm warning died. Regarding the underlined part, the following explanation is reasonable ()
The jellyfish received infrasound waves.
(b) Jellyfish receive electromagnetic waves.
The jellyfish felt a sudden change in temperature.
(d) Jellyfish feel the change of geomagnetic field.
(Anhui in 2005)
The hearing range of animals is generally wider than that of people. They can hear infrasound and ultrasonic waves that humans can't hear. Before the storm or earthquake comes, jellyfish can receive infrasound waves generated by seawater or crustal movement, so they can take refuge measures as soon as possible. The answer should be (a).
There is often such a feeling and experience in life: if you cover your ears with your hands when eating biscuits or hard and crisp food, you will hear a loud chewing sound, which shows that _ _ _ _ _ can transmit sound. But the students around you often can't hear the obvious voice. Why? Please make a reasonable guess from a physical point of view.
(Wuhu, 2005)
According to the analysis, people will make sounds when chewing food, and the chewing sounds they hear are mainly transmitted through bone conduction, so when they cover their ears with their hands, they will hear a lot of chewing sounds.
The chewing sound heard by others is mainly transmitted through the air. Students around you often can't hear obvious voices. It can be guessed that this is because the chewing sound spreads around in the process of spreading in the air, and the sound has reached the ears of the surrounding students very weakly.
3. Three characteristics of sound
Sound has three main characteristics: tone, loudness and timbre.
The tone is determined by the vibration frequency of the sound source. The higher the frequency, the higher the pitch.
Loudness is related to the amplitude of sound source vibration, and the greater the amplitude, the greater the loudness. Loudness is also related to the distance between people and sound sources. The farther and more dispersed the sound is, the smaller the sound people hear.
The timbre is related to the material and shape of the vocal body.
When insects fly, their wings vibrate. Butterflies flap their wings 5-6 times per second, and bees flap their wings 300-400 times per second. When they are all flying behind you, you should listen to your hearing ()
You can feel butterflies flying behind you.
You can feel bees flying behind you.
(c) You can feel them flying behind you.
(d) You can't feel them flying behind you.
(Panzhihua in 2005)
The frequency range of sound that can arouse people's hearing is 20 ~ 20~20000Hz (this data needs students' memory), and the number of times that butterfly wings vibrate per second is less than 20 times, which is out of people's hearing range, so people can't hear the sound of butterflies flying, but they can hear the sound of bees flying. So the answer should be (b).
Before a string band plays, the player should adjust the instrument, tighten or relax the strings, mainly to change the sound made by the instrument.
(a) Tone (b) Loudness
(c) timbre (d) propagation direction
It is analyzed that the factor affecting tone is frequency, the factor affecting loudness is amplitude, and the factor affecting timbre is the vocal body itself. Adjusting the tightness of strings can affect the vibration frequency of strings, that is, affect the timbre. The amplitude depends on the strength of plucking the string, and has nothing to do with the tightness of the string. So the answer is (a).
As shown in figure 1, the rabbit can tell that it is not her grandmother outside the door, mainly according to the voice ().
(a) loudness (b) timbre
(c) Tone (d) Frequency (Yantai, 2004)
Analyzing the timbre of people's voices varies from person to person. We can "distinguish people by their voices", mainly according to their timbre. Select "b"
As shown in Figure 2, the doctor is examining the patient with a stethoscope. Stethoscope uses the principle of sound (fill in "energy" or "information transmission"). The sound emitted by the patient is transmitted to the doctor's ear through the rubber tube, which can improve the _ _ _ _ _ _ _ (fill in "tone" or "loudness") of the sound. (Taizhou in 2005)
Figure 2
When analyzing the patient's discomfort, the sound emitted in the body may change, and the doctor can diagnose the patient through the change of the sound, so the sound has the function of transmitting information.
Doctors listen to the sound in the patient's body through a stethoscope in order to reduce the divergence of the sound in the process of transmission, thus increasing the loudness.
Example 9 As shown in Figure 3(a), Wu Shi used an oscilloscope, a hacksaw bar and a vise to study the loudness of sound. He clamped the lower end of the hacksaw bar to the bench, and pulled the upper end by hand to make the hacksaw bar vibrate and make a sound. In the experiment, he conducted two experiments. The first saw blade makes a loud noise, and the second saw blade makes a light noise. At the same time, he observed the waveform amplitude displayed on the oscilloscope as shown in Figure (b) and Figure (c) respectively, and he came to the experimental conclusion of _ _ _ _ _ _.
(Huanggang in 2005)
Figure 3
Through the analysis and comparison of Figure (b) and Figure (c), we can see that the amplitudes of the two vibrations are different, the first one is larger and the second one is smaller, which shows that loudness is related to the amplitude of the object vibration. The greater the amplitude, the greater the loudness; The smaller the amplitude, the smaller the loudness.
Xiao Ming wants to compare the sound insulation performance of several materials (clothes, tinfoil paper and foam plastic). In addition to the materials to be tested, there are also available equipment: tuning fork, mechanical alarm clock and shoe box. In this experiment is suitable for the sound source is _ _ _ _. Xiaoming put the sound source into the shoe box, which is full of materials to be tested. He conceived two experimental schemes (a) and (b), which you think is better.
(a) Let people stand at a certain distance from the shoe box and compare the loudness of the sound.
(b) Let people listen, and step back until they can't hear it. Compare the distance from here to the shoe box.
The phenomena obtained through experiments are shown in the following table. The order of sound insulation performance of the materials to be tested from good to bad is _ _ _ _ _ _ _.
(Yangzhou in 2005)
The mechanical alarm clock can ring for a long time, so it should be chosen as the sound source.
According to the experimental phenomena of the second group of "clothes" and "tin foil paper" in the table, it is "loud" and it is impossible to judge which material has the best sound insulation performance, so it is not feasible to adopt scheme (a), and scheme (b) should be chosen.
According to the first group of experimental phenomena, the sound insulation performance from good to bad is the summary of electrical knowledge of foam plastic, clothes and tin foil paper in turn.
First, the circuit
The formation of current: the directional movement of charge forms current.
Current direction: from the positive pole to the negative pole of the power supply.
Power supply: a device that can provide continuous current (or voltage).
Power supplies convert other forms of energy into electrical energy. For example, dry cells convert chemical energy into electrical energy. The generator converts mechanical energy into electrical energy.
Conditions for continuous current: power supply and circuit must be closed.
Conductor: Objects that are easy to conduct electricity are called conductors, such as metal, human body, earth, salt solution, etc.
Insulator: Objects that are not easy to conduct electricity are called insulators, such as glass, ceramics, plastics, oil and pure water.
Circuit composition: consists of power supply, wires, switches and electrical appliances.
The circuit has three states: (1) path: the connected circuit is called path; (2) Open circuit: A broken circuit is called an open circuit; (3) Short circuit: The circuit that directly connects the wires to the two poles of the power supply is called short circuit.
Circuit diagram: A diagram showing circuit connections with symbols is called a circuit diagram.
Series connection: connecting elements one by one in sequence is called series connection. If you disconnect anywhere, the current will disappear. )
Parallel connection: connecting elements in parallel is called parallel connection. (each branch does not affect each other. )
Second, at present
International unit: ampere (a); Commonly used: mA, microampere (A), 1 amp = 103 mA = 106 microampere.
The instrument for measuring current is: ammeter, and its usage rules are as follows: ① ammeter should be connected in series in the circuit; (2) Current flows from the "+"terminal and from the "-"terminal; (3) The measuring current should not exceed the range of ammeter; Never connect the ammeter to the two poles of the power supply without using electrical appliances.
The ammeter commonly used in the laboratory has two measuring ranges: ① 0 ~ 0.6 A, and the current represented by each battery is 0.02 A；; ② 0 ~ 3 A, and the current value represented by each unit is 0.1a. 。
Third, voltage.
Voltage (U): Voltage is the cause of current generation in the circuit, and power supply is the device that provides voltage.
International unit: Volt (V); Commonly used: KV, MV. 1kv = 103V = 106MV。
The instrument for measuring voltage is voltmeter, and the usage rules are as follows: ① The voltmeter should be connected in parallel in the circuit; (2) Current flows from the "+"terminal and from the "-"terminal; ③ The measured voltage should not exceed the range of voltmeter;
The voltmeter commonly used in the laboratory has two measuring ranges: ① 0 ~ 3 volts, and the voltage represented by each battery is 0. 1 volt;
② 0 ~15v, and the voltage represented by each cell is 0.5v..
Memory voltage value: ① 1 the voltage of dry cell is 1.5 volts; ② The voltage of1lead battery is 2 volts; (3) household lighting voltage is 220 volts; ④ safe voltage: not higher than 36V; ⑤ The industrial voltage is 380 volts.
Fourth, resistance.
Resistance (R): indicates the resistance of the conductor to the current. The greater the resistance of a conductor to current, the greater the resistance and the smaller the current passing through the conductor.
International unit: ohm (ω); Commonly used: Megaohms (mω), Kilohms (kω); 1 megohm =103kohm;
1 kω = 103 ω。
The factors that determine the resistance are material, length, cross-sectional area and temperature (R has nothing to do with its U and I).
Sliding rheostat:
Principle: Change the resistance by changing the length of the resistance wire in the circuit.
Function: Change the current and voltage in the circuit by changing the resistance in the circuit.
Nameplate: If the sliding rheostat is marked with "50Ω", it means that the maximum resistance is 50Ω and the maximum allowable current is 2A.
Correct use: a, should be used in series in the circuit; B, wiring should be "up and down"; C, the resistance value should be adjusted to the maximum before electrifying.
Ohm's Law
Ohm's Law: The current in a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.
Formula: where the unit is I→ an (a); U→ volt (v); R→ Europe (ω).
Understanding of the formula: ① I, U and R in the formula must be in the same circuit; ② If any two quantities of I, U and R are known, the other quantity can be found; (3) the unit should be unified when calculating.
Application of ohm's law;
(1) the resistance of the same resistor is constant, regardless of current and voltage, its current increases with the increase of voltage. (R=U/I)
② When the voltage is constant, the greater the resistance, the smaller the current (I=U/R).
(3) when the current is constant, the greater the resistance, the greater the voltage across the resistance. (U=IR)
The series connection of resistors has the following characteristics: (refer to R 1, R2 is connected in series, and the more series connections, the greater the resistance).
① Current: I=I 1=I2 (the currents in all parts of the series circuit are equal).
② voltage: U=U 1+U2 (the total voltage is equal to the sum of all voltages).
③ Resistance: R=R 1+R2 (total resistance is equal to the sum of all resistances). If n equivalent resistors are connected in series, R =nR.
④ partial pressure function: =; Calculate U 1, U2, available as:
⑤ Proportional relation: current: I1:I2 =1:1(q is heat).
The parallel connection of resistors has the following characteristics: (R 1, R2 is connected in parallel, and the more parallel connections, the smaller the resistance).
① Current: I=I 1+I2 (the main current is equal to the sum of the currents of each branch).
② voltage: U=U 1=U2 (main voltage is equal to each branch voltage).
③ Resistance: (the reciprocal of the total resistance is equal to the sum of the reciprocal of each resistance) If n equivalent resistances are connected in parallel, there is RTotal = R..
④ Shunt function: I 1 is calculated, and I2 is available:
⑤ Proportional relation: voltage: U 1:U2= 1: 1, (q is heat).
Intransitive verbs electricity and electricity
1. Electric work (w): The electric energy converted into other forms of energy is called electric work.
2. International unit of work: Joule. Commonly used: degree (kWh), 1 degree = 1 kWh =3.6× 106 Joule.
3. Tool for measuring power: electric energy meter
4. Electric power formula: W=Pt=UIt (where the unit is W→ Coke (J); U→ volt (v); I→an(a)； T→ seconds).
When calculating with W=UIt, it should be noted that: ① W.U.I and T in the formula are in the same circuit; (2) Units should be unified when calculating; ③ It is known that any three quantities can find the fourth quantity. There is another formula: =I2Rt.
Electric power (P): indicates the speed at which current does work. International unit: Watt (W); Commonly used unit: kW
Formula: where the unit is p → w; W→ coke; T→ seconds; U→ Volt (V), I→ An (A)
When using calculation, the unit should be unified. (1) if W uses coke, T uses seconds, and the unit of P is Watt; If w uses kWh, t uses hours, and the unit of p is kW.
10. The correct formula can also be used to calculate electric power: P=I2R, p = u2/r.
1 1. Rated voltage (U0): the normal working voltage of electrical appliances. In addition, the rated current.
12. Rated power (P0): the power of electrical appliances at rated voltage.
13. actual voltage (u): the voltage actually applied to the electrical appliance. In addition, the actual current.
14. actual power (p): the power of electrical appliances under actual voltage.
When U > U0, P > P0 is bright and easy to burn.
When u < U0, then p
When U = U0, then P = P0 emits light normally.
15. The same resistor, connected to different voltages, has; For example, when the actual voltage is half the rated voltage, the actual power is 1/4 rated power. For example, "220V 100W" is connected in the circuit of 1 10V, and the actual power is 25W. )
16. thermal power: the thermal power of a conductor is directly proportional to the square of the current and the resistance of the conductor.
17.P Thermal formula: P=I2Rt, (where the unit is p→ w); I→an(a)； R→ Europe (ω); T→ seconds. )
18. When all the work (electric work) done by current passing through a conductor is used to generate heat (electric heating), there is: thermal power = electric power, which can be calculated by electric power formula. (such as electric heaters, the resistance is like this. )
Seven. Household electricity consumption
The home circuit consists of incoming wires (live wire and neutral wire) → electric energy meter → master switch → safe → electrical appliances.
All household appliances are connected in parallel with sockets, and electrical appliances should be connected in series with their switches.
Fuse: made of lead-antimony alloy with high resistivity and low melting point. Its function is that when there is too much current in the circuit, it will heat up to the melting point and fuse, automatically cut off the circuit and play a safe role.
There are two reasons for excessive circuit current: one is short circuit; Second, the total power of electrical appliances is too large.
The principles of safe use of electricity are as follows: ① Don't touch low-voltage charged bodies; (2) don't close to the high voltage charged body.
Eight, electricity and magnetism
Magnetism: the property that an object attracts iron, nickel, cobalt and other substances.
Magnets: Magnetic objects are called magnets. It has directionality: north and south.
Magnetic pole: The strongest part of a magnet is called a magnetic pole.
Any magnet has two magnetic poles, one is the North Pole (N Pole); The other is the South Pole.
The function between magnetic poles: magnetic poles with the same name repel each other and magnetic poles with different names attract each other.
Magnetization: the process of magnetizing an object without magnetism.
There is a magnetic field around the magnet, and the interaction between magnetic poles occurs through the magnetic field.
Basic properties of magnetic field: the effect of magnetic force on magnets entering it.
Magnetic field direction: the direction of the north pole when the small magnetic needle is at rest is the magnetic field direction at this point.
Magnetic induction line: an imaginary curve describing the strength and direction of magnetic field. It doesn't exist or intersect, and it goes out in the north and enters in the south.
At a certain point in the magnetic field, the direction of the magnetic field and the direction of the magnetic induction line are the same.
10. The geomagnetic north pole is near the geographical south pole; The geomagnetic south pole is near the geographical north pole, but they do not overlap. Their intersection angle is called magnetic declination, which was first described by China scholar Shen Kuo.
1 1. Oster experiment proves that there is a magnetic field around the electrified wire.
12. Ampere's Law: Hold the solenoid with the right hand and bend it in the direction of the current in the solenoid with four points.
Then the end pointed by the thumb is the north pole (N pole) of the solenoid.
13. Characteristics of energized solenoid: ① The greater the current, the stronger the magnetism; ② The more turns of the coil, the stronger the magnetism; ③ Inserting a soft iron core greatly enhances the magnetism; ④ The polarity of the energized solenoid can be changed by the current direction.
14. electromagnet: a solenoid with an iron core inside constitutes an electromagnet.
15. characteristics of electromagnet: ① magnetism is controlled by the on-off of current; ② The magnetic force can be adjusted by changing the current and the number of turns of the coil; ③ The current direction can change the magnetic pole.
16. electromagnetic relay: it is essentially a switch controlled by electromagnet. Its function can realize remote operation, low voltage and weak current control high voltage and strong current, and realize automatic control.
17. Basic principle of telephone: vibration → changing current → vibration.
18. electromagnetic induction: when a part of the conductor of a closed circuit cuts a magnetic induction line in a magnetic field, a current is generated in the conductor. This phenomenon is called electromagnetic induction, and the generated current is called induced current. Application: Generator.
Conditions of induced current: ① The circuit must be closed; (2) Only a part of the conductor of the circuit is in the magnetic field; ③ This part of the conductor moves to cut the magnetic induction line.
Direction of induced current: It is related to the movement of conductor and the direction of magnetic induction line.
Generator principle: electromagnetic induction phenomenon. Structure: stator and rotor. It converts mechanical energy into electrical energy.
Influence of magnetic field on current: live wire will be acted by magnetic force in magnetic field. It is converted from electric energy to mechanical energy. Application: Motor.
The force direction of charged conductor in magnetic field is related to the direction of current and magnetic induction line.
Motor principle: it is made by using the principle that the electrified coil is forced to rotate in the magnetic field.
Commutator: realize the interchange of alternating current and direct current.
Alternating current: a current that periodically changes the direction of the current.
Direct current: current with constant direction.
experiment
1. Voltammetric resistance measurement
Experimental principle: (experimental equipment, circuit diagram is shown on the right) Note: Before the experiment, the sliding rheostat should be adjusted to the maximum resistance.
The function of sliding rheostat in the experiment is to change the voltage across the measured resistor.
2. Measuring the electric power of small light bulbs-experimental principle: P=UI