Explanation

• Transformers are used to change AC voltage levels,
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• AC stands for 'alternating current' which means the current constantly changes direction.
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• concept about transformer:
• A transformer is a device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage
  

Explanation

•  nylon  is a synthetic fiber
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• Rayon, Polyester, Nylon, Acrylic, and Plastic are the different types of synthetic fibers.
  

Explanation

•  crystal is an example of instructive igneous rock
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• instructive rock is also known as plutonic rock.

Explanation

The seismic velocity increases gradually with the depth of the mantle as the pressure increases with depth  and therefore the density increases.

Explanation

The first evidence of helium was observed on August 18, 1868

 as a bright yellow line with a wavelength of 587.49-nanometers in the spectrum of the chromosphere of the Sun.

The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India.

Explanation

An s-orbital is spherical with the nucleus at its center,

a p-orbitals is dumbbell-shaped

and four of the five d orbitals are cloverleaf shaped.

Explanation

Mendeleev is best known for discovering periodic law in 1869.

Explanation

The four main types of steel:

1. Carbon Steel,
2. Alloy Steel,
3. Tool Steel
4. Stainless Steel.
   

Explanation

A fluorescent lamp consists of a glass tube filled with a mixture of argon and mercury vapour.

Explanation

Overall, the Earth is about 1.59% aluminium by mass