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:
h=12.41m
Explanation:
N=392
r=0.6m
w=24 rad/s

So the weight of the wheel is the force N divide on the gravity and also can find momentum of inertia to determine the kinetic energy at motion


moment of inertia

Kinetic energy of the rotation motion

Kinetic energy translational

Total kinetic energy

Now the work done by the friction is acting at the motion so the kinetic energy and the work of motion give the potential work so there we can find height

To solve this problem we will apply the concepts related to pressure, depending on the product between the density of the fluid, the gravity and the depth / height at which it is located.
For mercury, density, gravity and height are defined as



For the air the defined properties would be



We have for equilibrium that


Replacing,

Rearranging to find 


Therefore the elevation of the mountain top is 9400ft
You should check A, and D.
The Arctic Ocean is the smallest ocean. It is more than five times smaller than Indian and Atlantic Oceans.