The correct answer of this question is : A) Change alternating current into direct current.
EXPLANATION :
As per the question, we are given vacuum tube. Vacuum tube can be of various types. Normally it contains two electrodes called cathode and anode which are enclosed in an evacuated glass chamber . There are also other types of vacuum tubes which contain extra electrodes like control grid .
The vacuum tube can be used as a rectifier. It means that it can be used as an electronic device which will convert alternating current into direct current. It may be a half wave rectifier or a full wave rectifier. Actually the direct current obtained during the rectification of alternating current is pulsating in nature.
Hence, the correct answer is that a vacuum tube can be used to change alternating current into direct current.
Answer:

It will take 10 seconds to travel 200m at a speed of 10m/s
Explanation:
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Displacement = (straight-line distance between the start point and end point) .
Since the road east is perpendicular to the road north,
the car drove two legs of a right triangle, and the magnitude
of its final displacement is the hypotenuse of the triangle.
Length of the hypotenuse = √ (215² + 45²)
= √ (46,225 + 2,025)
= √ 48,250
= 219.7 miles .
Answer:
208.33 W
141.26626 seconds
Explanation:
E = Energy = 
t = Time taken = 8 h
m = Mass = 2000 kg
g = Acceleration due to gravity = 9.81 m/s²
h = Height of platform = 1.5 m
Power is obtained when we divide energy by time

The average useful power output of the person is 208.33 W
The energy in the next part would be the potential energy
The time taken would be

The time taken to lift the load is 141.26626 seconds
It's cold outside, the water vaper in your breath condenses into tiny droplets of liquid water and ice that you can see.