Eighth grade physics

1. The electrons emitted from the filament at the tail of the picture tube hit the TV screen at high speed, making the screen glow and hit the picture tube (B).

A. TV uses alternating current, and the current in the picture tube is constantly changing.

The direction of the current is from the fluorescent screen to the filament.

The direction of the current is from the filament to the fluorescent screen.

D. the inside of the picture tube is vacuum, and current cannot pass through it.

2. The following statement is true (A)

A. the direction of current always flows from the positive electrode to the negative electrode.

B. the directional movement of positive and negative charges can form current.

C the current direction of the metal conductor is consistent with the directional movement direction of the free electrons.

D. None of the above statements is true.

3. The switch for controlling the light bulb is between the light bulb and the optional live or zero line.

4. Copper wire is neutral under normal circumstances. When it is connected with electrical appliances, switches and power sources to form a path, the directional movement of (electrons) in the copper wire forms a current, and the direction of its directional movement is opposite to that of the current.

In sports, researchers often use stroboscopic photography to analyze and guide athletes' movements. Stroboscopic photography means that when the photographic light source flashes rhythmically, the light emitted by the light source shines on the athletes and reflects (diffuses), and then forms a (shadow) image in front of the camera through the lens. When stroboscopic photography is needed, whether the background (dark) is bright or dark.

6. Besides sprinkling salt on the road surface in winter can avoid or reduce traffic accidents, what other methods are commonly used?

What is the truth?

Adding anti-skid chains to automobile tires can increase the friction coefficient between tires and the ground.