Grade 8 Physics Rush !!!

Option C Because it was a close-up of the face, the object is closer to the lens.

Now you're going to take a full-body shot, and the object is farther away from the lens, and the image distance is shorter.

A: A doesn't need to adjust anything else, just move back a bit. In fact, the distance between the object and the lens becomes farther away, but the image distance does not become shorter, and the image will be blurry.

b: Stepping back and extending the lens of the camera forward does not guarantee that the object will be farther away from the lens.

C: If you step back a little bit, and at the same time retract the lens of the camera a little bit, you will be farther away from the lens.

D: If you move forward, and the lens of the camera is a little bit forward, the object is closer to the lens, no.

Answer: After taking a close-up of the face, shoot the whole body **, which is equivalent to the image becoming smaller, according to the principle of "the object is far away and the near image becomes smaller", that is, the object distance becomes larger, and the image and image distance become smaller.

At this point, the person should move away from the camera, and the lens of the camera should be retracted so that the negative is closer to the lens.

So, choose: c

cLingling retreats a little, and at the same time retracts the lens of the camera a little, because if you want to take a full-body photo, it will be smaller, and the distance between objects will become larger, so you should retreat;

And when the object distance is larger, the image distance will be smaller, so the lens is retracted a little back.

From the "head" to the "full-body photo", the object distance should be increased and the image distance should be reduced"c""Move back a bit": Increase the object distance""The lens of the camera is retracted a little": Reduce the image distance.

1. Calculate the conspiracy of the stone: 14g 5cm 3=

2. Mass = volume * density = 30m 3 * tons.

Start by calculating the density of granite.

p = m v14 5 g per cubic centimeter.

The quality of the granite monument.

m=PV14 5 30 10 6 = to the 7th power g=84t

You're in Kunba, right? Density = 14 5 Mass = 14 5 * 1000 * 30 kg = 84000kg = 84t

Calculated by proportion, let m stele = x, then x: 14 = 30 3: 5 3

(1), t = 13 hours and 30 minutes =

v=s/t=1463km/

2) The time mentioned by the reporter refers to the time taken by the train to run non-stop at a maximum speed of 160 kilometers per hour is 9 hours and 8 minutes, but in fact, the car has to enter and exit the station, and get on and off passengers. So the speed won't always be 160 km/h. It's going to be smaller.

So it will actually take a little more time.

Please click here, you can ask if you don't know.

Actual time t=13 hours and 30 minutes=

Average speed = total distance t=1463km

The reporter's calculation was based on the top speed of the whole journey, and did not take into account the stop time of the intermediate stops.

(1)1463/

2) The reporter uses the maximum speed of the train as the average speed of the actual operation of the train, but the maximum speed of the train is only a few times in operation that can be reached, and most of the time it is accelerating and decelerating, such as entering and exiting the station and entering and exiting the corner, so it is unscientific to use the maximum speed as the average speed, which is very different from the actual situation.

Flute membrane, resonance, air column, short.

The air column becomes shorter, the frequency increases, and the pitch is higher.

1. Since the neon lamp emits light, it proves that the current is composed of a closed circuit composed of the live wire (- electrical appliances) - the human body - the earth, so the live wire is intact. Then it can only mean that the neutral line is broken (or faulty).

2. (The title itself is a bit contradictory).

1) The bolt board and the jack may form a short circuit, or the bolt board itself has an unknown fault (2) Either do not use that socket, or overhaul that socket 3, no, how can it be connected like this?

According to the topic, the socket is connected in parallel with the switch, that is, the socket is connected in parallel with the live wire. When you plug the light into the socket (the switch is disconnected), neither light will work properly!

Question 1; The so-called zero line is broken.

The second question, there is a problem with the socket line on the wall, if you know how to walk the line, you can go again. Otherwise, don't use that jack.

The third question, no, the light switch actually only controls one line, it is recommended that you use two dry batteries and a flashlight bulb for experiments.

Water has the property of abnormal expansion. (at 4 degrees Celsius).

Generally, when things are hot, the volume expands, and the density decreases accordingly, and when it is cold, the volume decreases, and the density increases.

But water between 4 100 is thermal expansion and contraction, and 0 4 is thermal contraction and cold contraction. The density of water is highest at 4 degrees Celsius.

So in waters with a lot of freshwater, not all waters are the same temperature.

When the water starts to get cold, the water at 4 degrees Celsius becomes densest and sinks to the bottom, and the water at 1 degrees Celsius or 2 degrees Celsius or less floats on the surface.

When the air temperature is around 0 degrees, the temperature of the large freshwater area from top to bottom is like this:

The water with low temperature is on the top.

The high temperature of 4 degrees Celsius is at the bottom.

The rest of the water 0 4 is heat contraction and cold expansion to the top to the bottom of the temperature in order to increase the arrangement.

Waters o degrees.

Lower o-degree.

1 degree 2 degrees. 3 degrees, 4 degrees at the bottom.

At the bottom of the water is the earth.

Therefore, when the air temperature is lower than 0 degrees, the water on the surface of the lake freezes first, and as the temperature gets lower and lower, the freezing range extends to the water below the water, but the thickness of the ice maintains the temperature of the water below, so the water under the ice layer will not freeze.

In addition, in seawater, the composition of the water increases a lot, and the freezing point of NaCl itself also rises, and the lower it goes, the higher the salt concentration, the less likely it is to freeze.

So to sum up, the water down there doesn't freeze, but it has to be over a large area of water!!

This water 0 4 is the nature of heat contraction and cold expansion, and it is also the reason why we humans can survive

There are two conditions that must be met for water to freeze, one is zero degrees, and the other is to continue to cool down, and water will not freeze when placed at a constant temperature of zero degrees. Ice is a poor conductor of heat, and the heat transfer performance is not good, so the water cannot continue to lower the temperature, so that the water under the ice is always above zero, so it will not freeze.

According to p = w t, the same work, that is, w is the same, t a: t b = w p a: w p b, it is not difficult to calculate the time ratio is.

2:3 also uses the formula p=w t, the time is the same, w a: w b is equal to p a t a: p b t b is equal to the power ratio, that is, 3:2