A. 10 ohm 0.2 amp
B. 10 ohm 2 amp
10 ohm 1 amp
D.20 ohms 1 amp
1994, comet Sumer-Levi broke into more than 20 pieces and crashed into Jupiter, causing a huge explosion, but people on earth did not hear a sound. This is because: ()
The fragments of this comet are too small to be weighed.
B.the sound produced by the explosion is too weak to be heard.
C. Space is an ideal vacuum without sound propagation.
D. Jupiter is too far away from the earth to hear.
We live in a world of sound, and sound is everywhere. In the following sounds: ① the roar of machines in the factory workshop; (2) the performance of musical instruments in the theater; (3) the chirping of birds in the park in the morning; (4) the sound of the electric drill when decorating the house; (5) firecrackers at the wedding; (5) the sound of the mountain stream gurgling; This kind of noise belongs to ().
A.①③④
B.①②⑤
C.①④⑤
D.①④⑤⑥
A. Connect a resistor with appropriate resistance in parallel on the A lamp.
B. Connect a resistor with appropriate resistance in series on the A lamp.
C, connect a resistor with an appropriate resistance in series with the lamp B ..
D, connect a resistor with appropriate resistance in parallel with the lamp B.
If the two metal foils of the electroscope are opened due to electrification, the two metal foils must be ()
A. positively charged
B. negatively charged
C. Same crime
D. with heterogeneous charges
A. the direction of current is from b to a, and the direction of free electron movement is from b to a.
B. the direction of current is from a to b, and the direction of free electron movement is from b to a.
C. the direction of current is from a to b, and the direction of free electron movement is from a to B.
D. the direction of current is from b to a, and the direction of free electron movement is from a to B.
In the following cases, there must be a current through ()
A. charged objects
B. a conductor with a moving charge
C. a circuit with voltage at both ends
D. electrical appliances that consume electricity.
People see the image of the moon and fish in the pond. What is their formation? ( )
A. it's all refraction.
B. The former is a refraction phenomenon and the latter is a reflection phenomenon.
C.this is all a reflection phenomenon.
D. The former is a reflection phenomenon and the latter is a refraction phenomenon.
The included angle between the incident light and the plane mirror is 35. When the plane mirror is rotated to increase the incident angle by 5, the included angle between the reflected light and the incident light becomes ().
A: 70
b80
C. 1 10
D. 120
There is an ancient poem that says: "When I was young, I didn't know the moon, so I called it Bai Yupan;" I also suspect that Yao Taijing is flying at the end of Qingyun Mountain. "Judging from your knowledge of physics, moonlight is ()
A. light from the moon itself
B. specular reflection of sunlight
C. diffuse reflection of sunlight
D. reflected light from nine planets
On a sunny night after rain, in order not to step on the water on the ground, the following judgment is correct []
A. Walking against the moonlight, the water is in the dark place on the ground, while walking against the moonlight, the water is in the bright place on the ground.
B. Go against the moonlight, the water shines on the ground, go against the moonlight, and the water is in the dark.
C. When walking against the moonlight or with the moonlight on your back, the water should shine on the ground.
D. walking against the moonlight or walking with the moonlight on your back should be the water in the darkness on the ground.
Among the following phenomena, belongs to the phenomenon of light refraction is []
A. I saw that the water in the swimming pool was shallower than it actually was.
All the students in the classroom can see the words on the blackboard clearly.
C.white clouds are reflected on the lake.
D. See your own image in the flat mirror.
Some animals can hardly see anything at night, while owls have good eyesight at night. This is because the owl's eyes ().
A. you can see the target without infrared rays.
B. Self-luminous, illuminating the search target.
C.it can produce infrared vision.
D. it can produce vision for ultraviolet rays.
The glass rod rubbed with silk is close to a foam ball, and the correct statement is ().
A. If the ball is attracted, it must be negatively charged.
B. If the ball is attracted, it may be negatively charged.
If the ball is attracted, it must be uncharged.
If the ball is attracted, it may be positively charged.
Two charged bodies are not charged after contact, indicating that their original electricity is ().
A. the same cost
B. Heterogeneous charge
C. the equivalent of the same cost
D. Equal heterogeneous charge
The following statement is true ()
A. the headlights of cars use flat mirrors.
B. The rearview mirror of a car is a convex mirror.
C. solar cookers use convex mirrors.
D. The mirror that dentists use to observe the parts that patients can't easily see is concave mirror.
The following changes are exothermic ()
A. melting, gasification and sublimation
B. Solidification, liquefaction and sublimation
C. melting, liquefaction and sublimation
D. solidification, gasification and sublimation
The following changes need to absorb heat is ()
A. frosting
B. Dew formation
C. Ice turns into water
D. water turned into ice
Echo measurement () cannot be used in the following situations.
A. Seabed depth
B. Measure the distance to the opposite cliff.
C. location of benthic fish resources
D. measure the distance to the moon
Sometimes when you think it's quiet and there is no sound, the dog will suddenly be very alert. This is because: ()
A. The dog's ears can rotate to accurately confirm the direction of sound.
B. dogs have higher vocal frequency than others.
C. dogs have a higher hearing frequency than people.
D. the same sound, the dog's voice is very loud.
A classmate knocks once, beats the same drum face once, and makes two sounds ()
A. different tones
B. Different frequencies
C. Different loudness
D. Different timbres
When mom buys bowls, she often touches two bowls gently and listens to the sound. She mainly judges the quality of the bowl according to the sound.
A. Tone
B. Volume
C. timbre
D. volume
The following statement is wrong: ()
A. After an object passes through the lens of an ordinary camera, it becomes a reduced image on the negative.
B the optical center of the lens is located on its main optical axis.
C. the real images formed by convex lenses are all reduced.
D. the virtual images formed by convex lenses are all positive.
Spread a piece of transparent plastic paper on the horizontal desktop, drop a small drop of water on the plastic paper with chopsticks, hold the plastic paper close to the newspaper with both hands, and read the words on the newspaper through the drops of water. What you see is: ()
A. Inverted characters, enlarged real images
B. Inverted characters, enlarged virtual images
C. Honest person, enlarged real image
D. erect and enlarged virtual images of words
This object is not in the focus of the convex lens. If you want to make it smaller, you should ()
A. Increase the object distance and image distance
B. Reduce object distance and image distance
C. Increase the object distance and reduce the image distance
D. Increase the image distance and reduce the object distance.
The distance from the object to the mirror surface of the plane mirror is 2m, so the distance from the image of the object in the plane mirror to the mirror surface is ().
A. 1m
B.3m
C.4m
D.2m
About real image and virtual image, the following statement is correct ()
A. The virtual image is the illusion of people, and no light enters the human eye.
B The real image must be formed by refraction of light, and the virtual image must be formed by reflection of light.
C. the light screen can receive the real image, but the virtual image cannot.
D. the plane mirror becomes a virtual image and the convex lens becomes a real image.
The following statement is wrong: ()
A. After an object passes through the lens of an ordinary camera, it becomes a reduced image on the negative.
B the optical center of the lens is located on its main optical axis.
C. the real images formed by convex lenses are all reduced.
D. the virtual images formed by convex lenses are all positive.
Regarding the specific heat capacity, the following statement is correct ()
A. The greater the mass of iron, the greater its specific heat.
B. The more heat a copper block absorbs, the greater its specific heat.
C the copper block with high temperature has higher specific heat than the iron block with low temperature.
D. specific heat is a characteristic of matter, which has nothing to do with the mass, temperature and heat absorption of the object.
Shen Kuo Memorial Hall will cast a bronze statue in memory of Shen Kuo. In the process of casting bronze statue with copper block, the state change of copper block is ().
A. sublimation first, then concentration.
B. first concentrate, then sublimate.
C, melting first and then curing.
D, curing first, and then melting.
After a hot bath in the bathroom, the glass mirror in the room becomes blurred, and after a while, the mirror becomes clear again. The two state changes of the mirror image are ()
A. vaporizing first, then liquefying;
B, liquefying first, and then vaporizing;
C. only liquefaction;
D. only vaporization
A.A
B.B
C.C
D.D
A.b and d terminals
B.a and d terminals
C.c and d terminals
D.a and b terminals
Put the following objects in a magnetic field, which will not be affected by the magnetic force is ()
A. nickel rod
B. copper bar
C. iron sheet
D. small magnetic needle
A steel bar is close to a small magnet, and the N pole of the small magnet is attracted to the steel bar. This phenomenon shows that steel bars are originally ().
A. It must be magnetic, and the end near the magnetic is the S pole.
B.it must be magnetic, but its polarity cannot be determined.
C. Can't be magnetic
D. not necessarily magnetic
The working principle of electric bell is ()
A. the magnetic effect of current
B. Thermal effect of current
C. chemical effects of current
D. None of the above statements is true.
There are 25 classrooms in the whole school, and each classroom has 6 40W lights, which saves electricity for half an hour every day on average, so one month (30 days) can save electricity ().
A. 15kWh
90 kilowatt hours
About 900 kwh
D. unable to calculate
Two electric lamps, L 1 marked with "6V 3W" and L2 unmarked, measured the resistance of L2 as 6Ω. When they are connected in series in a certain circuit, they can all emit light normally, so the voltage across the circuit and the electric power of L2 are () respectively.
A. 12V 3W
B. 12V 1.5W
C.9V 3W
D.9V 1.5W
Two different bulbs are connected at both ends of a power supply, and the currents flowing through the two bulbs are not equal as measured by an ammeter, so the connection mode of the two bulbs is ().
A. it must be in series.
B. it must be parallel.
C. both series and parallel connection are acceptable.
D. insufficient conditions to judge
The following electrical equipment, the use of current thermal effect is ().
A. electric motor
B. rice cooker
C. electric fan
D. TV set
The current intensity through the electrical appliance is 0.2 A, and the work done by the current in 10 minute is 240 J, so the voltage across the electrical appliance is ().
A. 120
B.60 volts
C. 10/0v
D.2 volts
When several students are discussing power supply, voltage and current, the correct one is ().
A. where there is voltage, there is power supply and current.
B. Where there is power supply, there is voltage and current.
C. where there is current, there is power supply and voltage.
D. if there is a power supply and a voltage at the same time, there must be a current.
Electric fans, incandescent lamps and soldering irons are all marked with the words "220V, 60W". When working normally, the heat generated at the same time ()
A. most electric fans
B. incandescent lamp is the most
C. Electric soldering iron is the most
D. There are as many as three
About the conductor resistance, the correct is ()
A. If two wires with the same thickness are long, the resistance must be large.
B. If the cross-sectional area of two wires with the same length is small, the resistance must be large.
C two wires made of the same material, with the same length and small cross-sectional area must have high resistance.
The resistance of aluminum conductor must be greater than that of copper conductor.
In order to protect consumers' rights and interests, a technical quality supervision department conducted spot checks on wire products on the market, and found that the diameter of copper core in a brand wire was obviously smaller than the diameter specified in the wire specification, resulting in excessive resistance. From the analysis of the factors affecting the conductor resistance, the main reason for this kind of conductor resistance is ()
A. the length of the wire
B. Cross-sectional area of electric wire
C. Wire materials
D. Temperature of the wire
The following phenomena cannot be explained by light traveling in a straight line: ()
A. When planting young trees, they can be planted in a straight line by visual inspection.
B. solar eclipse phenomenon
C.you can see the moon in the water on the shore.
D. Shadows of objects under light
The object becomes a real image on the light screen through the convex lens. If the lens is covered with paper at this time, ()
A. There are no images on the screen.
B.the image on the screen is half of the original.
C. you have to move the screen to get a clear image.
D. the screen is still the original picture, but it is a little darker than the original picture.
About the knowledge of the circuit, the following statement is incorrect ()
A. In order to make two lights turn on and off at the same time, the two lights must be connected in series.
B. the current in metal is formed by the directional motion of free electrons.
C in the circuit, the power supply is a device that converts other forms of energy into electrical energy.
D. The general circuit consists of power supply, electrical appliances, switches and wires.
A beam of light is reflected on the surface of an object, and the reflected light is perpendicular to the incident light, then ()
A. the incident angle is 45 degrees.
B. the incident angle is 90 degrees.
C. the reflection angle is 45.
D. the incident light is perpendicular to the surface of the object.
The following statement is true ()
A. The light shines vertically on the plane mirror with an incident angle of 90.
B. diffuse reflection also obeys the law of reflection.
C If the included angle between the reflected light and the incident light is 120, the incident angle is 60.
D It takes about 500s for the light from the sun to reach the earth, so the distance from the sun to the earth is about 1.5× 108km.
The following statement is true ()
A. the light emitted by fluorescent lamps also contains ultraviolet rays.
B ancient paintings can be identified by the characteristics of different substances emitting different colors of fluorescence under ultraviolet radiation.
C infrared remote sensing technology can be used to survey the earth, find water sources, monitor forest fires, estimate crop growth in a large area, and predict storms and cold waves.
D. everything is constantly emitting infrared rays and absorbing infrared rays. The higher the temperature of an object, the more infrared rays it radiates.
The use of infrared rays in the following items is ()
A. night vision goggles
B. Automatic sensing faucet
C. automatic induction door
D. remote control
The following statement is wrong: ()
A. The real images formed by the convex lens are all objects and images on both sides of the convex lens.
B. The virtual images formed by the convex lens are all objects, and the images are on the same side of the convex lens.
C. The real images formed by convex lenses are all inverted.
D. the virtual image formed by the convex lens is either enlarged or reduced.
When using a magnifying glass, when the object is 8 cm away from the lens and you see a clear image, judge its focal length. What is incorrect is ().
A. not more than 8 cm;
B. not less than 8 cm;
C. it must not be equal to 8 cm;
D. it can't be 5cm.
About real image and virtual image, the following statement is correct ()
A. Virtual image is a human illusion, and no light enters the human eye;
B. The real image must be formed by refraction of light, and the virtual image must be formed by reflection of light.
C. the light screen can receive the real image, but the virtual image cannot.
D. the plane mirror becomes a virtual image and the convex lens becomes a real image.
About the lens, the following statement is correct ()
A. concave lens has divergent effect on light.
B. The lenses of reading glasses are concave lenses.
C. the lens of a camera is equivalent to a convex lens. When you take a picture with it, you can get an inverted enlarged real image.
D. Projectors made of convex lenses can get magnified virtual images on the screen.
Column belongs to the noise is ()
A. The symphony Destiny was played in the concert hall.
B. At home, several classmates are singing songs like nobody's watching.
C. low-flying jets
D. The sound of sharp nails hitting aluminum pot
Alcoholics Anonymous and Alcoholics Anonymous
Alcoholics Anonymous and Alcoholics Anonymous
B.b and c
B.b and c
C.a and d
C.a and d
D.b and d
D.b and d
A. if there is a major change in the current representation, s should be followed by a.
B. If the current indicator changes significantly, S should be followed by B..
C. If the voltage indicates a significant change, S should be followed by one.
D. if there is a significant change in voltage representation, s should be followed by B.
A.①
B.②
C.③
D.④
A. the light bulb doesn't work
B. the ammeter pointer has obvious deflection.
C. the ammeter is burnt out.
D. voltage means that the number is the voltage of the power supply.
The two lamps L 1 and L2 have the same rated power, but the rated voltage is u 1 > U2. The following statement is correct ().
A. I2 < i 1 when the second lamp emits light normally.
B. the resistance of the two filaments r 1 < R2.
C. when two lamps are used in series, the actual power p2 > p 1.
D. when two lamps are used in parallel, the actual power is p' 2 > p' 1.
A. the stress in figure (a) is minimum;
B. The stress direction of each drawing is the same;
C. the force on each picture is the same;
D. not sure.
Comparison between electrostatic field and magnetic field: ()
A. the electric field line is not closed and the magnetic induction line is closed;
Both electrostatic field and magnetic field can deflect the moving charge;
C. Both electrostatic field and magnetic field can accelerate the moving charge;
D. Both electrostatic field and magnetic field can do work on moving charge.
An electric heater is marked with the words "220V 1000W". There are four opinions about this electric heater, and the wrong one is ().
A. it can work normally when connected to a home circuit.
B. In normal operation, the power consumption per second is1000 w w.
The current through the normal workpiece is about 4.5A
In normal operation, its resistance is about 49 Ω.
In the home lighting circuit, the more electrical appliances are connected, the correct one in the following statement is ().
A. the greater the total current in the circuit.
B. the greater the total voltage in the circuit.
C. the greater the total resistance in the circuit.
D. the greater the total power in the circuit.
About the knowledge of the circuit, the following statement is incorrect ()
A. In order to make two lights turn on and off at the same time, the two lights must be connected in series.
B. the current in metal is formed by the directional motion of free electrons.
C in the circuit, the power supply is a device that converts other forms of energy into electrical energy.
D. The general circuit consists of power supply, electrical appliances, switches and wires.
The voltage across A.l 1 is 2 volts.
The voltage of B.L2 is 2 volts.
C the sum of the voltages between the power supply and L 1 is 2 volts.
The voltage across D.L 1 is 4 volts.
The following household appliances, do not use the thermal effect of current is ().
A. rice cooker
B. Electric razor
C. iron
D. electric furnace