A simple physics problem in the first year of junior high school

1) Experimental principle:

Speed = distance time.

2) Experimental equipment:

A transparent cassette tape, a tape recorder, a stopwatch, and a ruler.

3) Experimental Procedure:

1。Rewind the tape all the way down and measure the tape. Measure the length of the tape from the head to the empty shaft.

3。Analyze the results of the calculations.

4) The physical quantities that need to be recorded.

The actual tape goes through head length l2

The tape length of the head to the empty hinge is l1

The actual tape goes through head length l2

The tape length of the head to the empty hinge is l1

Known: l=75m l=2*l1+l2

Find v:v=l t

Substitution to solve.

1) Know the distance, according to the time, find the speed

1、s=vt

2. Stopwatch, solo player.

3. Repeat several times to average and calculate the speed.

It is right to choose BA virtual image can not be undertaken, [according to the definition of virtual reality] B is wrong. The magnifying glass is virtual and positive.

Flat mirror imaging is also positive.

Note: The inversion of the image is not the inversion of the virtual image and the real thing, but is related to the normal perpendicular to the plane mirror, and the image is inverted when the image and the object are on both sides of the normal.

c Reality can only be seen after it has been inherited, so reality must be inherited.

The difference between a real image and a virtual image is that the actual light of the real image (convergence), the virtual image is formed by the actual light (the intersection of the reverse extension line), and the (real) image can be presented on the light screen, while the (virtual) image cannot.

The Concept of Real Image and Virtual Image Real image: The refraction of the refracted line emitted by the object point through the lens, all the refractive lines can converge at a point, the point is called the real image point of the object point, and the set of all the real image points is called the image of the object. The characteristics of the real image are:

The intersection of the reverse extension of the refractive line of the light emitted by the object point through the lens is called the virtual image point of the object point, and its set is called the virtual image of the object. The characteristics of the virtual image are: it is not the convergence of the actual light, it is upright, and the same side cannot be formed on the screen 2 Imaging rules:

Object distance (p) Nature of the image Size Positive and inverted virtual real p>2f Reduced inverted real image p=2f Equal large inverted real image 2f>p>f Enlarged inverted real image p

A is right, the virtual image is just the image that the human eye sees through the plane mirror, take a light screen and put it in front of the plane mirror, and you will find it.

b. This method is inaccurate and therefore wrong.

C is right, because you can't find counterexamples to overturn.

D is right, I won't say more.

Note that the diameter of another coil of thin copper wire is d2

Wrap the diameter d1 around a certain length s in a pencil, and write down the number of turns n1, and the unknown one also wraps around the length s just now on the pencil, and write down the number of turns, so d2 n1*d1 n2.

Let gasoline internal energy W1 and diesel W2, then:

25%w1=35%w2

w1/w2=35%/25%=7：5