1. With this statement, the author is referring to the fact that the vehicles are one of the largest polluters of the air. In order to reduce the pollution, the vehicles that are used will need to be changed, and with it the pollution will decrease significantly. The reduction of the pollution will come because the vehicles on hydrogen will not cause any pollution, so the enormous amounts of carbon dioxide released from the combustion of the engines will be thing of the past.
2. There are several challenges with this type of vehicles in order for them to replace the fossil fuel driven ones. The big price is one of the factors, as the majority of the people can not afford these cars. Another problem is that these vehicles are not as fast as the fossil fuel driven ones, and lot of people enjoy fast driving, despite it not being safe. There are millions of vehicles out there on the roads, and changing all of them with hydrogen vehicles will take a lot of time, as lot of those vehicles are new ones, so the people will not be willing to just throw them away and leave them rot in their garages. In order for the change of the driving park to be accomplished, the prices should go down, the people to be more serious about the environment and its protection, and patience as several decades will probably be needed for a change like this to be competed.
3. The fuel celled cars are a viable answer to decrease the pollution, as they are not causing any pollution, but instead will stop the process of large emissions of carbon dioxide from the fossil fueled cars. While this method is a good one, it should not be the only, as on its own it can not have the desirable effect, but instead all the major polluters should be included in the process. The industry and the production of energy are one of the major polluters as well, so they will need to follow the example, as if they not, the problem will stay, considering that the industry is constantly growing and the demand for energy is constantly growing too.
Answer
When an electric current flows in a wire, it creates a magnetic field around the wire. This effect can be used to make an electromagnet. A simple electromagnet comprises a length of wire turned into a coil and connected to a battery or power supply.
A coil of insulated wire is wrapped around an iron nail. One end of the coil of wire is connected to a battery. The other is connected to a switch in the circuit
A simple electromagnet
You can make an electromagnet stronger by doing these things:
wrapping the coil around a piece of iron (such as an iron nail)
adding more turns to the coil
increasing the current flowing through the coil
There is a limit to how much current can be passed safely through the wire because the resistance of the wire causes heating.
Answer:
B.Law of conservation of energy
Explanation:
In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time. This law means that energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.
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Energy is 4 * 
J
The rate of dissipation is 2 * 
W
In the question, it is given that
t = 20 s
R = 400 mm
L = 300 mm
where t, R, and L are time, radius, and length.
For magnetic energy density, the formula is
ηo = Energy / volume
= β^2 / 2 * μ
Now, substituting the values
= 
/ 2 * 4 * Π * 
= 1.59 * 
J / m^3
Now, energy is
= energy density * volume
= 1.59 * * Π * 0.5 * 
= 4 * J
The rate of dissipation is
= Energy / time
= 4 * / 20
= 2 * W
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